面试学习总结

之前根据视频做的总结，备个份。

一、Volatile关键字

volatile是Java虚拟机提供的轻量级的同步机制。

三个特性：

1. 保证可见性

   线程修改了工作内存中的值并写回到主内存之后，主内存立刻通知所有线程。称为可见性。（结合JMM理解）

   代码演示可见性+原子性代码

   import java.util.concurrent.TimeUnit;
   
   /**
    * 1. 验证volatile可见性
    * 1.1 假如number=0，number变量之前没有添加volatile关键字，没有可见性。
    *
    * @author shiwenquan
    * @Create 2020-12-10 16:16
    * @description
    */
   public class VolatileDemo {
   
       public static void main(String[] args) {
           MyData myData = new MyData();
           new Thread(() -> {
               System.out.println(Thread.currentThread().getName() + "\t come in");
               //睡眠三秒
               try {TimeUnit.SECONDS.sleep(3);} catch (InterruptedException e) {e.printStackTrace();}
               myData.addT060();
               System.out.println(Thread.currentThread().getName() + "\t update number value: " + myData.number);
           }, "AAA").start();
   
   
           // 第二个main线程
           while (myData.number == 0) {
               // main线程一直在这里等待循环，直到number不等于0
   
               // 如果不添加volatile关键字，会一直循环，因为此时没有可见性。
           }
           System.out.println(Thread.currentThread().getName() + "\t minssion is over, main is value" + myData.number);
   
       }
   
   }
   
   class MyData {
   
       volatile int number = 0;
       public void addT060() {
           this.number = 60;
       }
   }
   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26
   27
   28
   29
   30
   31
   32
   33
   34
   35
   36
   37
   38
   39
   40
   41
   42

2. 不保证原子性

   volatile不保证原子性代码验证

   /**
    * 1. 验证volatile可见性
    *  1.1 假如number=0，number变量之前没有添加volatile关键字，没有可见性。
    *  1.2 添加了volatile，可以解决可见性问题。
    *
    * 2. 验证volatile不保证原子性
    *  2.1 原子性指的是什么意思？
    *      不可分割，完整性。要么同时成功要么同时失败。
    *  2.2 volatile不保证原子性案例。
    *
    * @author shiwenquan
    * @Create 2020-12-10 16:16
    * @description
    */
   public class VolatileDemo {
   
       public static void main(String[] args) {
           MyData myData = new MyData();
   
           for (int i = 0; i < 20; i++) {
               new Thread(() -> {
                   for (int j = 0; j < 1000; j++) {
                       myData.addPlusPlus();
                   }
               },String.valueOf(i)).start();
           }
   
           // 需要等待所有线程计算完成之后，计算最终结果。
           while (Thread.activeCount() > 2){
               Thread.yield();
           }
           System.out.println(Thread.currentThread().getName()+"\t number value: " + myData.number);
   
       }
   
   
   }
   
   class MyData {
   
       volatile int number = 0;
   
       // 此时number前面加了volatile
       public void addPlusPlus(){
           number++;
       }
   }
   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26
   27
   28
   29
   30
   31
   32
   33
   34
   35
   36
   37
   38
   39
   40
   41
   42
   43
   44
   45
   46
   47

3. 禁止指令重排（指令重排结合JMM的有序性查看）
   volatile实现禁止指令重排优化，从而避免多线程环境下程序出现乱序执行的现象。

JMM(Java内存模型)(Volatile补充)

是一种抽象概念并不真实存在，它描述是一组规则或规范，通过规范定义了程序中各个变量（包括实例字段，静态字段和构成数组对象的元素）的访问方式。

由于JVM运行程序的实体是线程，而每个线程创建时JVM都会为其创建一个工作内存（有些地方称为栈空间），工作内存是每个线程的私有数据区域，而Java内存模型中规定所有变量都存储在主内存，主内存是共享内存区域，所有线程都可访问，但线程对变量的操作（读取赋值等）必须在工作内存中进行，首先要将变量从主内存拷贝到自己的工作内存空间，然后对变量进行操作，操作完成后再将变量写回主内存。不能直接操作主内存中的变量，各个线程中的工作内存里存储着主内存中的变量副本拷贝，因此不同的线程间无法访问对方的工作内存，线程间的通信（传值）必须通过主内存来完成，其简要访问过程如下图：

JMM关于同步的规定：

1. 线程加锁前，必须把共享变量的值刷新回主内存
2. 线程加锁前，必须读取主内存的最新值到自己的工作内存
3. 加锁解锁是同一把锁

特性：

1. 可见性

2. 原子性

3. 有序性

   计算机在执行程序时，为了提高性能，编译器和处理器常常会对指令做重排。一般分为一下3种。

   | 源代码 | --> | 编译器优化的重排 | --> | 指令并行的重排 | --> | 内存系统的重排 | --> | 最终执行的指令 |

   单线程环境里确保程序最终执行结果和代码顺序执行结果一致。

   处理器在进行重排序时必须要考虑指令之间的数据依赖性。

   多线程环境中线程交替执行，由于编译器优化重排的存在，两个线程中使用的变量能否保证一致性是无法确定的，结果无法预测。

单例模式在多线程环境下出现的问题

问题实例代码，可以在getInstance()方法前加synchronized关键字来避免这个问题，但是synchronized直接加在方法上不推荐，效率会急剧降低。

/**
 * @author shiwenquan
 * @Create 2020-12-11 13:46
 * @description
 */
public class SingletonDemo {

    private static SingletonDemo instance = null;

    private SingletonDemo(){
        System.out.println(Thread.currentThread().getName() + "\t 构造方法。。");
    }

    public static SingletonDemo getInstance(){
        if (instance == null){
            instance = new SingletonDemo();
        }
        return instance;
    }

    public static void main(String[] args) {
        // 单线程
/*        System.out.println(SingletonDemo.getInstance() == SingletonDemo.instance);
        System.out.println(SingletonDemo.getInstance() == SingletonDemo.instance);
        System.out.println(SingletonDemo.getInstance() == SingletonDemo.instance);*/

        // 多线程并发
        for (int i = 0; i < 10; i++) {
            new Thread(() -> {
                SingletonDemo.getInstance();
            },String.valueOf(i)).start();
        }
    }

}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35

修正之后（DCL案例），为减少代码这里只贴getInstance()方法的代码：

DCL（双端检查）机制不一定安全，因为时有指令重排的存在，加入volatile可以禁止指令重排。

原因在于某一个线程执行到第一次检测，读取到的instance不为null时，instance的引用对象可能没有完成初始化。

instance = new SingletonDemo();可以分为3布完成（伪代码）

memory = allocate();//1.分配对象内存空间

instance(memory);//2.初始化对象

instance = memory;//3.设置instance指向刚分配的内存地址，此时instance!=null

2和3不存在数据依赖关系，而且无论重排前还是重排后程序的执行结果在单线程中没有改变，因此这种重排优化时允许的。

memory = allocate();//1.分配对象内存空间

instance = memory;//3.设置instance指向刚分配的内存地址，此时instance!=null，但是此时对象还没有初始化完成！

instance(memory);//2.初始化对象

但是指令重排只会保证串行语义执行的一致性（单线程），但并不会关心多线程间的语义一致性。

所以当一条线程访问instance不为null时，由于instance实例未必已经初始化完成，也就造成了线程安全问题。

    // DCL(Double Check Lock双端检锁机制)
    public static synchronized SingletonDemo getInstance(){
        if (instance == null){
            synchronized (SingletonDemo.class){
                if (instance == null){
                    instance = new SingletonDemo();
                }
            }
        }
        return instance;
    }
1
2
3
4
5
6
7
8
9
10
11

这样修改之后绝大部分情况都不会出现线程安全问题，并不绝对，因为编译里和处理器有可能做指令重排，重排之后可能还会出现创建多个对象的问题。volatile可以禁止指令重排，于是可以在变量前面用volatile关键字修饰。

最后代码：

/**
 * @author shiwenquan
 * @Create 2020-12-11 13:46
 * @description
 */
public class SingletonDemo {

    private volatile static SingletonDemo instance = null;

    private SingletonDemo(){
        System.out.println(Thread.currentThread().getName() + "\t 构造方法。。");
    }

    // DCL(Double Check Lock双端检锁机制)
    public static synchronized SingletonDemo getInstance(){
        if (instance == null){
            synchronized (SingletonDemo.class){
                if (instance == null){
                    instance = new SingletonDemo();
                }
            }
        }
        return instance;
    }

    public static void main(String[] args) {
        // 单线程
/*        System.out.println(SingletonDemo.getInstance() == SingletonDemo.instance);
        System.out.println(SingletonDemo.getInstance() == SingletonDemo.instance);
        System.out.println(SingletonDemo.getInstance() == SingletonDemo.instance);*/

        // 多线程并发
        for (int i = 0; i < 10; i++) {
            new Thread(() -> {
                SingletonDemo.getInstance();
            },String.valueOf(i)).start();
        }
    }

}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40

二、CAS

什么是CAS？

全称Compare-And-Swap并比较并交换，它是CPU并发原语。

它的功能是判断内存某个位置的值是否为预期值，如果是则更改为新的值，这个过程是原子的。

CAS并发原语体现在Java语言中就是sun.misc.Unsafe类中的各个方法。调用Unsafe类中的CAS方法，JVM会帮我们实现出CAS汇编指令。这是一种完全依赖于硬件的功能，通过它实现原子操作。再次强调，由于CAS是一种系统原语，原语属于操作系统用语范畴，是由若干条指令组成的，用于完成某个功能的一个过程，并且原语的执行必须是连续的，在执行过程中不允许被中断，也就是说CAS是一条CPU的原子指令，不会造成所谓的数据不一致问题。

compareAndSet()

如果当前值==期望值，则以原子方式将该值设置为给定的更新值

参数：

​ 期望值，更新值

返回值：

​ 如果成功返回true，错误返回false

示例代码：

    public static void main(String[] args) {

        AtomicInteger atomicInteger = new AtomicInteger(5);

        System.out.println(atomicInteger.compareAndSet(5, 2019)+ "\t  update : " + atomicInteger.get());
        System.out.println(atomicInteger.compareAndSet(5, 1024)+ "\t  update : " + atomicInteger.get());

    }
1
2
3
4
5
6
7
8

Unsafe

1. Unsafe是CAS的核心类，由于Java方法无法直接访问底层系统，需要通过本地（native）方法来访问，Unsafe相当于一个后门，基于该类可以直接操作特定内存的数据。Unsafe类存在于sun.misc包中，其内部方法操作可以像C的指针一样直接操作内存，因为Java中CAS操作的执行依赖于Unsafe类的方法。

   注意：Unsafe类中的所有方法都是native修饰的，也就是说Unsafe类中的方法都是直接调用操作系统底层资源，执行相应任务。

2. 变量valueOffset，表示该变量值在内存中的偏移地址，因为Unsafe就是根据内存偏移地址来获取数据的。

       /**
        * Atomically increments by one the current value.
        *
        * @return the previous value
        */
       public final int getAndIncrement() {
           return unsafe.getAndAddInt(this, valueOffset, 1);
       }
   1
   2
   3
   4
   5
   6
   7
   8

3. 变量value用volatile修饰，保证了多线程之间的内存可见性。

CAS缺点

1. 循环时间长开销大（do while）

2. 只能保证一个共享变量的原子操作

   当对一个共享变量执行操作时，可以使用CAS方式来保证原子操作，但是对多个共享变量操作时，循环CAS就无法保证操作的原子性，这个时候就需要锁来保证原子性。

3. ABA问题

   假如有两个线程，线程一从内存位置V中取出A，这时候另一个线程二也从内存中取出A，并且线程二进行了一些操作将值变成了B，然后线程二又将V位置的数据变成A，这时候线程一进行CAS操作发现内存中仍是A，然后线程一操作成功。

   尽管线程一的CAS操作成功，但是不代表这个过程就是没问题的。

4. 原子引用
   原子引用实例代码（无法避免ABA问题）：

   import java.util.concurrent.atomic.AtomicReference;
   
   class User {
       String userName;
       int age;
   
       public User(String userName, int age) {
           this.userName = userName;
           this.age = age;
       }
   
       public String getUserName() {
           return userName;
       }
   
       public void setUserName(String userName) {
           this.userName = userName;
       }
   
       public int getAge() {
           return age;
       }
   
       public void setAge(int age) {
           this.age = age;
       }
   
       @Override
       public String toString() {
           return "User{" +
                   "userName='" + userName + '\'' +
                   ", age=" + age +
                   '}';
       }
   }
   
   /**
    * @author shiwenquan
    * @Create 2020-12-14 9:28
    * @description
    */
   public class AtomicReferenceDemo {
       public static void main(String[] args) {
           User z3 = new User("z3", 22);
           User l4 = new User("l4", 23);
   
           AtomicReference<User> reference = new AtomicReference<>();
           reference.set(z3);
   
           boolean b = reference.compareAndSet(z3, l4);
           System.out.println(b + "\t " + reference.get().toString());
   
       }
   }
   
   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26
   27
   28
   29
   30
   31
   32
   33
   34
   35
   36
   37
   38
   39
   40
   41
   42
   43
   44
   45
   46
   47
   48
   49
   50
   51
   52
   53
   54
   55

三、集合类不安全之并发修改异常

集合类线程不安全之List

代码实例：

/**
 * 集合类不安全问题
 *      java.util.ConcurrentModificationException  异常
 * @author shiwenquan
 * @Create 2020-12-14 10:11
 * @description
 */
public class ContainerNotSageDemo {
    public static void main(String[] args) {
/*        List list = new ArrayList<>();
        List list = new Vector<>();
        List list = Collections.synchronizedList(new ArrayList<>());*/
        List<String> list = new CopyOnWriteArrayList<>();
        list.add("1");

        for (int i = 0; i < 30; i++) {
            new Thread(()->{
                // java.util.ConcurrentModificationException  异常
                list.add(UUID.randomUUID().toString().substring(0,8));
                System.out.println(Thread.currentThread().getName()+list);
            },String.valueOf(i)).start();
        }

        /**
         * 1.故障现象
         *      java.util.ConcurrentModificationException
         *
         * 2.导致原因
         *      并发争抢修改导致，一个线程正在写，另一个线程来抢，导致数据不一致。
         *
         * 3.解决方案
         *      3.1 使用new Vector<>();
         *      3.2 使用Collections.synchronizedList(new ArrayList<>());
         *      3.3 使用new CopyOnWriteArrayList<>();
         *
         * 4.优化建议
         *      写时复制：CopyOnWrite容器即写时复制的容器。往一个容器添加元素的时候，不直接往当前容器Object[]添加，而是先将当前容器
         *      Object[]进行copy，复制出一个新的容器Object[] newElements，然后在新的容器Object[] newElements里添加元素，添加元素
         *      之后再将原容器的引用指向新的容器 setArray(newElements)。这样做的好处是可以对CopyOnWrite容器进行并发读，而不需要加锁，
         *      因为当前容器不会添加任何元素。所以CopyOnWrite容器也是一种读写分离的思想。读和写不同的容器。
         *      
         *     CopyOnWrite的add方法源码：
         *     Appends the specified element to the end of this list.
         *     @param e element to be appended to this list
         *     @return {@code true} (as specified by {@link Collection#add})
         *     
         *     public boolean add(E e) {
         *         final ReentrantLock lock = this.lock;
         *         lock.lock();
         *         try {
         *             Object[] elements = getArray();
         *             int len = elements.length;
         *             Object[] newElements = Arrays.copyOf(elements, len + 1);
         *             newElements[len] = e;
         *             setArray(newElements);
         *             return true;
         *         } finally {
         *             lock.unlock();
         *         }
         *     }
         */
    }
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62

集合类线程不安全之Set

实例代码：（错误和解决办法和List类似）

//        Set set = new HashSet<>();
//        Set set = Collections.synchronizedSet(new HashSet<>());
        Set<String> set = new CopyOnWriteArraySet<>();

        for (int i = 0; i < 30; i++) {
            new Thread(()->{
                // java.util.ConcurrentModificationException  异常
                set.add(UUID.randomUUID().toString().substring(0,8));
                System.out.println(Thread.currentThread().getName()+set);
            },String.valueOf(i)).start();
        }
1
2
3
4
5
6
7
8
9
10
11

集合类线程不安全之Map

实例代码：（用ConcurrentHashMap解决）

//        Map map = new HashMap<>();
//        Map map = Collections.synchronizedMap(new HashMap<>());
        Map<String,String> map = new ConcurrentHashMap<>();

        for (int i = 0; i < 30; i++) {
            new Thread(()->{
                // java.util.ConcurrentModificationException  异常
                map.put(Thread.currentThread().getName(),UUID.randomUUID().toString().substring(0,8));
                System.out.println(Thread.currentThread().getName()+map);
            },String.valueOf(i)).start();
        }

1
2
3
4
5
6
7
8
9
10
11
12

四、锁

公平锁和非公平锁

公平锁：指多个线程按照申请锁的顺序来获得锁。

非公平锁：指多个线程获取锁的顺序并不是按照申请锁的顺序，有可能后申请的线程比先申请的线程优先获取锁。在高并发的情况下，有可能会造成优先级反转或者饥饿现象。

可重入锁（递归锁）

指的是同一线程外层函数获得锁之后，内层递归函数仍能获取该锁的代码，在同一个线程在外层方法获取锁的时候，进入内层方法锁会自动获取锁。

也就说，线程可以进入任何一个它已经拥有的锁 所同步着的代码块。

ReentrantLock/Synchronized就是典型的可重入锁。

最大作用就是避免死锁。

可重入锁代码示例：

class Phone{
    public synchronized void sendSMS() throws Exception{
        System.out.println(Thread.currentThread().getId()+"\t   sendSMS方法。。");
        sendEmail();
    }
    public synchronized void sendEmail() throws Exception{
        System.out.println(Thread.currentThread().getId()+"\t   sendEmail方法。。");
    }
}


/**
 * @author shiwenquan
 * @Create 2020-12-14 14:50
 * @description
 */
public class ReenterLockDemo {

    public static void main(String[] args) {
        Phone phone = new Phone();
        
        for (int i = 0; i < 2; i++) {
            new Thread(()->{
                try {
                    phone.sendSMS();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            },String.valueOf(i)).start();
        }

        /**
         * 输出：
         * 11	   sendSMS方法。。
         * 11	   sendEmail方法。。
         * 12	   sendSMS方法。。
         * 12	   sendEmail方法。。
         */
    }

}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41

独占锁（写锁）/共享锁（读锁）/互斥锁

独占：指该锁一次只能被一个线程所持有。ReentrantLock和Synchronized而言都是独占锁。

共享：指该锁可被多个线程所持有。对ReentrantReadWriteLock其读锁是共享锁，写锁是独占锁。读锁的共享锁可保证并发读是非常高效的，读写，写读，写写的过程是互斥的。

代码示例：

/**
 * 资源类
 */
class MyCache{

    private volatile Map<String, Object> map = new HashMap<>();
    private ReentrantReadWriteLock rwLock = new ReentrantReadWriteLock();

    public void put(String key, Object value){
        rwLock.writeLock().lock();
        try {
            System.out.println(Thread.currentThread().getName()+"\t 正在写入："+key);
            try {
                // 暂停线程一会
                TimeUnit.MILLISECONDS.sleep(300);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            map.put(key,value);
            System.out.println(Thread.currentThread().getName()+"\t 写入完成。");
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            rwLock.writeLock().unlock();
        }

    }

    public void get(String key){
        rwLock.readLock().lock();
        try {
            System.out.println(Thread.currentThread().getName()+"\t 正在读取。");
            try {
                // 暂停线程一会
                TimeUnit.MILLISECONDS.sleep(300);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            Object result = map.get(key);
            System.out.println(Thread.currentThread().getName()+"\t 读取完成："+result);
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            rwLock.readLock().unlock();
        }
    }

}

/**
 * 多线程同时读一个资源类没有任何问题，所以为了满足并发量，读取共享资源应该可以同时进行。
 * 但是如果有一个线程想去写共享资源，就不应该再有其他线程可以对该资源进行读或写。
 *
 * 小总结：
 *      读-读     能共存
 *      读-写     不能共存
 *      写-写     不能共存
 *
 *      写操作：原子+独占，中间整个过程必须是一个完整的统一体，中间不许被分割或者打断。
 *
 * @author shiwenquan
 * @Create 2020-12-14 15:43
 * @description
 */
public class ReadWriteLockDemo{
    public static void main(String[] args) {
        MyCache myCache = new MyCache();

        for (int i = 0; i < 5; i++) {
            final int tempInt = i;
            new Thread(()->{
                myCache.put(tempInt+"", tempInt+"");
            },String.valueOf(i)).start();
        }


        for (int i = 0; i < 5; i++) {
            final int tempInt = i;
            new Thread(()->{
                myCache.get(tempInt+"");
            },String.valueOf(i)).start();
        }
    }
}

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85

自旋锁

是指尝试获取锁的线程不会立即阻塞，而是采用循环的方式去尝试获取锁，这样的好处是减少线程上下文切换的消耗，缺点是循环会消耗CPU。

代码示例：

public class SpinLockDemo {

    AtomicReference<Thread> atomicReference = new AtomicReference<>();

    public void myLook(){
        Thread thread = Thread.currentThread();
        // 自旋
        while (!atomicReference.compareAndSet(null, thread)){

        }
        System.out.println(thread.getName()+"获得锁。。");
    }

    public void myUnLock(){
        Thread thread = Thread.currentThread();
        atomicReference.compareAndSet(thread, null);
        System.out.println(thread.getName()+"释放锁。。");

    }

    public static void main(String[] args) throws InterruptedException {
        SpinLockDemo demo = new SpinLockDemo();

        new Thread(()->{
            demo.myLook();
            try {
                TimeUnit.SECONDS.sleep(10);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            demo.myUnLock();
        },"t1").start();

        // 确保线程一先获得锁。
        TimeUnit.SECONDS.sleep(2);

        new Thread(()->{
            demo.myLook();
            demo.myUnLock();
        },"t2").start();

    }
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43

CountDownLath/CyclicBarrier/Semaphone

1. CountDownLath
   让一些线程阻塞直到另一些线程完成一系列操作后才被唤醒。
   主要有两个方法，当一个或者多个线程调用await方法时，调用线程会被阻塞。其它线程调用countDown方法会将计数器减 1（调用countDown方法的线程不会阻塞），当计数器的值变为零时，因调用await方法被阻塞的线程会被唤醒，继续执行。

   代码实例：

   public class CountDownLatchDemo {
       public static void main(String[] args) {
   
           CountDownLatch latch = new CountDownLatch(6);
   
           for (int i = 0; i < 6; i++) {
               new Thread(()->{
                   System.out.println(Thread.currentThread().getName()+"\t 结束。");
                   latch.countDown();
                   try {
                       TimeUnit.SECONDS.sleep(5);
                   } catch (InterruptedException e) {
                       e.printStackTrace();
                   }
                   System.out.println(Thread.currentThread().getName()+"\t 结束。。");
               },String.valueOf(i)).start();
           }
   
           try {
               latch.await();
           } catch (InterruptedException e) {
               e.printStackTrace();
           }
           System.out.println(Thread.currentThread().getName()+"\t main结束。");
       }
   }
   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26

   注意结果（当计数器变成零时，不管线程是否已经结束，被阻塞的线程会被立即唤醒）：

   0 结束。
   1 结束。
   2 结束。
   3 结束。
   4 结束。
   5 结束。
   main main结束。
   3 结束。。
   5 结束。。
   0 结束。。
   1 结束。。
   4 结束。。
   2 结束。。

2. CyclicBarrier
   CyclicBarrier的字面意思时可循环（Cyclic）使用的屏障（Barrier）。它要做的事情是让一组线程到达一个屏障（也可以叫同步点）时被阻塞，直到最后一个线程达到屏障时，屏障才会开门，所有被屏障拦截的线程才会继续干活，线程进入屏障通过CyclicBarrier的await()方法。

   public class CyclicBarrierDemo {
       public static void main(String[] args) {
           CyclicBarrier barrier = new CyclicBarrier(7, ()->{
               System.out.println("---------");
           });
   
   
           for (int i = 0; i < 7; i++) {
               final int tempInt = i;
               new Thread(()->{
                   System.out.println(Thread.currentThread().getName()+"\t 第" + tempInt + "个！");
                   try {
                       barrier.await();
                   } catch (InterruptedException e) {
                       e.printStackTrace();
                   } catch (BrokenBarrierException e) {
                       e.printStackTrace();
                   }
                   
                   try {
                       TimeUnit.SECONDS.sleep(5);
                   } catch (InterruptedException e) {
                       e.printStackTrace();
                   }
                   System.out.println(Thread.currentThread().getName()+"\t 结束。。");
               },String.valueOf(i)).start();
           }
       }
   }
   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26
   27
   28
   29

   注意结果（和CountDownLath差不多，不管线程是否已经结束，被阻塞的线程会被立即唤醒）：

   0 第0个！
   1 第1个！
   2 第2个！
   3 第3个！
   4 第4个！
   5 第5个！
   6 第6个！
   ---------
   0 结束。。
   6 结束。。
   5 结束。。
   1 结束。。
   2 结束。。
   4 结束。。
   3 结束。。

3. Semaphore
   Semaphore(信号灯)主要有两个目的，一个用于多个共享资源的互斥使用，另一个用于并发线程数的控制。
   代码示例：

   public class SemaphoreDemo {
       public static void main(String[] args) {
           // 模拟三个停车位
           Semaphore semaphore = new Semaphore(3);
           // 模拟六个汽车
           for (int i = 0; i < 6; i++) {
               new Thread(()->{
                   try {
                       semaphore.acquire();
                       System.out.println(Thread.currentThread().getName()+"\t 抢到车位。");
                       TimeUnit.SECONDS.sleep(3);
                       System.out.println(Thread.currentThread().getName()+"\t 离开车位。");
                   } catch (InterruptedException e) {
                       e.printStackTrace();
                   }finally {
                       semaphore.release();
                   }
               },String.valueOf(i)).start();
           }
       }
   }
   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21

五、队列

队列+阻塞队列（BlockintQueue）

阻塞队列：首先是一个队列，而一个阻塞队列在数据结构中所起的作用大致是，线程1往阻塞队列中添加元素，而线程2从阻塞队列中移除元素。

当阻塞队列是空时，从队列中获取元素的操作会被阻塞。

当队列是满的时候，往队列中添加元素的操作将会被阻塞。

有七种：

• ArrayBlockintQueue：由数组结构组成的有界阻塞队列。
• LinkedBlockingQueue：由链表结构组成的有界（但默认值为Integer.MAX_VALUE）阻塞队列。
• PriorityBlockingQueue：支持优先级排序的无界阻塞队列。
• DelayQueue：使用优先级队列实现的延迟误解阻塞队列。
• SynchronousQueue：不存储元素的阻塞队列，即单个元素队列。
• LinkedTransferQueue：由链表组成的无界阻塞队列。
• LinkedBlockingDeque：由链表结构组成的双向阻塞队列。

BlockingQueue核心方法：

抛出异常：

• 当阻塞队列满时，再往队列add插入元素会抛IllegalStateException：Queue full
• 当阻塞队列空时，再往队列remove移除元素会抛NoSuchElementException

特殊值：

• 插入方法，成功true失败false
• 移除方法，成功返回队列里的元素，队列里面没有就返回null

一直阻塞：

• 当阻塞队列满时，生产者线程继续往队列里put元素，队列会一直阻塞生产线程直到put数据or响应中断退出。
• 当阻塞队列空时，消费者试图从队列里take元素，队列会一直阻塞消费者线程直到队列可用。

超时退出：

• 当阻塞队列满时，队列会阻塞生产者线程一定时间，超过限时时间后生产者线程会退出。

用在哪里？

• 生产者消费者模式

1. 传统版代码示例：

   /**
    * 题目：一个初始值为零的变量，两个线程交替操作，一个加1一个减一，来五次
    *
    *      1. 线程   操作(方法)  资源类
    *      2. 判断   干活  通知
    *      3. 防止虚假唤醒机制
    *
    * @author shiwenquan
    * @Create 2020-12-16 14:34
    * @description
    */
   public class ProdConsumer_TraditionDemo {
   
       private static int i = 0;
   
       public static void main(String[] args) throws InterruptedException {
           ShareData data = new ShareData();
           new Thread(()->{
               for (int j = 0; j < 5; j++) {
                   data.decrement();
                   try {
                       TimeUnit.SECONDS.sleep(2);
                   } catch (InterruptedException e) {
                       e.printStackTrace();
                   }
               }
           },"AA").start();
           new Thread(()->{
               for (int j = 0; j < 5; j++) {
                   data.increment();
               }
           },"BB").start();
       }
   }
   
   
   class ShareData{
       private int number;
       private Lock lock = new ReentrantLock();
       private Condition condition = lock.newCondition();
   
       // 加
       public void increment() {
           lock.lock();
           try {
               // 1. 判断
               while (number != 0){
                   // 等待，不能生产
                   condition.await();
               }
               // 2.干活
               number++;
               System.out.println(Thread.currentThread().getName()+"\t "+number);
               // 3. 通知唤醒
               condition.signal();
           }catch (Exception e){
               e.printStackTrace();
           }finally {
               lock.unlock();
           }
       }
   
   
       // 减
       public void decrement() {
           lock.lock();
           try {
               // 1. 判断
               while (number == 0){
                   // 等待，不能生产
                   condition.await();
               }
               // 2.干活
               number--;
               System.out.println(Thread.currentThread().getName()+"\t "+number);
               // 3. 通知唤醒
               condition.signal();
           }catch (Exception e){
               e.printStackTrace();
           }finally {
               lock.unlock();
           }
       }
   
   }
   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26
   27
   28
   29
   30
   31
   32
   33
   34
   35
   36
   37
   38
   39
   40
   41
   42
   43
   44
   45
   46
   47
   48
   49
   50
   51
   52
   53
   54
   55
   56
   57
   58
   59
   60
   61
   62
   63
   64
   65
   66
   67
   68
   69
   70
   71
   72
   73
   74
   75
   76
   77
   78
   79
   80
   81
   82
   83
   84
   85

2. 阻塞队列版代码示例：

   /**
    * volatile/CAS/atomicInteger/blockQueue/线程交互/原子引用
    *
    * @author shiwenquan
    * @Create 2020-12-16 14:35
    * @description
    */
   public class ProdConsumer_BlockQueueDemo {
       public static void main(String[] args) {
           MyResource resource = new MyResource(new ArrayBlockingQueue<>(10));
   
           new Thread(()->{
               System.out.println(Thread.currentThread().getName()+"\t 生产线程启动！");
               try {
                   resource.myProd();
               } catch (Exception e) {
                   e.printStackTrace();
               }
           },"prod").start();
   
           new Thread(()->{
               System.out.println(Thread.currentThread().getName()+"\t 消费线程启动！");
               try {
   
                   try {
                       // 线程睡眠4秒钟
                       TimeUnit.SECONDS.sleep(4);
                   } catch (InterruptedException e) {e.printStackTrace();}
                   resource.myConsumer();
               } catch (Exception e) {
                   e.printStackTrace();
               }
           },"consumer").start();
   
           try {
               // 线程睡眠10秒钟
               TimeUnit.SECONDS.sleep(10);
           } catch (InterruptedException e) {e.printStackTrace();}
   
           System.out.println();
           System.out.println();
           System.out.println();
           System.out.println("10秒钟后，停止生产线程");
           resource.stop();
       }
   }
   
   
   class MyResource{
       /*
        默认开启，进行生产+消费
        */
       private volatile boolean FLAG = true;
       private AtomicInteger atomicInteger = new AtomicInteger();
   
       BlockingQueue<String> blockingQueue = null;
       public MyResource(BlockingQueue<String> blockingQueue) {
           System.out.println(blockingQueue.getClass().getName());
           this.blockingQueue = blockingQueue;
       }
   
       public void myProd() throws Exception{
           String data = null;
           boolean retValue;
           while (FLAG){
               data = String.valueOf(atomicInteger.incrementAndGet());
               retValue = blockingQueue.offer(data, 2L, TimeUnit.SECONDS);
               if (retValue){
                   System.out.println(Thread.currentThread().getName()+"\t 插入队列"+data+"成功！");
               }else{
                   System.out.println(Thread.currentThread().getName()+"\t 插入队列"+data+"失败！");
               }
   
               try {
                   // 线程睡眠1秒钟
                   TimeUnit.SECONDS.sleep(1);
               } catch (InterruptedException e) {e.printStackTrace();}
           }
   
           System.out.println(Thread.currentThread().getName()+"\t 线程停止，生产动作结束！");
       }
   
       public void myConsumer() throws Exception{
           String result = null;
           while (FLAG){
               result = blockingQueue.poll(4L,TimeUnit.SECONDS);
               if (null == result||result.equalsIgnoreCase("")){
                   FLAG = false;
                   System.out.println(Thread.currentThread().getName()+"\t 超过4秒没有消费，消费退出");
                   return;
               }
               System.out.println(Thread.currentThread().getName()+"\t 消费队列"+result+"成功！");
           }
       }
   
       public void stop(){
           this.FLAG = false;
       }
   
   }
   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26
   27
   28
   29
   30
   31
   32
   33
   34
   35
   36
   37
   38
   39
   40
   41
   42
   43
   44
   45
   46
   47
   48
   49
   50
   51
   52
   53
   54
   55
   56
   57
   58
   59
   60
   61
   62
   63
   64
   65
   66
   67
   68
   69
   70
   71
   72
   73
   74
   75
   76
   77
   78
   79
   80
   81
   82
   83
   84
   85
   86
   87
   88
   89
   90
   91
   92
   93
   94
   95
   96
   97
   98
   99
   100

• 线程池
• 消息中间间

有什么好处？为什么用？为什么需要？

在多线程领域：所谓阻塞，在某些情况下会挂起线程（即阻塞），一旦条件满足，被挂起的线程又会自动被唤醒。

好处是我们u需要关心什么时候需要阻塞线程，什么时候需要唤醒线程，因为Blocking Queue都包办了。

在concurrent包发布以前，在多线程环境下，我们每个程序员都必须自己控制这些细节，尤其还要兼顾效率和线程安全，而这会给们的程序带来不小的复杂度。

六、Synchronized和Lock有什么区别？用新的lock有什么好处？

1. 原始结构

Synchronized是关键字属于JVM层面，编译之后Synchronized会有monitorenter和monitorexit

​ monitorenter（底层是通过monitor对象来完成，其实wait/notify等方法也依赖于monitor对象只有在同步方法块或方法中才能调wait/notify等方法）

​ monitorexit

lock是类，api层面的锁。
synchronized反编译之后会生成一个monitorenter和两个monitorexit，monitorenter用于上锁，monitorexit用于去掉锁，有两个是防止报异常之后锁不释放。

2. 使用方法

Synchronized 不需要用户手动释放锁，当Synchronized 代码执行完后系统会让线程释放对锁的占用
ReentrantLock 需要 用户主动释放锁，如果没有主动释放则可能会导致出现死锁问题。

3. 等待是否可中断

Synchronized 不可中断，除非抛出异常或者正常运行。
ReentrantLock 可中断。设置超时方法tryLock(long timeout, TimeUnit unit); lockInterruptibly()放入代码块中，调用interr()方法可中断。

4. 加锁是否公平

Synchronized 非公平锁
ReentrantLock 两种锁都可以，默认非公平锁，构造方法可以传入Boolean值

5. 锁绑定多个条件condition

Synchronized 没有
ReentrantLock 用来实现分组唤醒需要唤醒的县城们，可以精确唤醒，而不像Synchronized 要么随机唤醒要么全部唤醒

精确唤醒指定线程案例：

/**
 * 题目：多线程之间按顺序调用，实现A->B->C三个线程启动，要求如下
 * AA打印五次，BB打印十次，CC打印十五次
 * 紧接着
 * AA打印五次，BB打印十次，CC打印十五次
 * ......
 * 来十轮
 * 
 * @author shiwenquan
 * @Create 2020-12-16 15:20
 * @description
 */
public class SyncAndLockDemo {
    public static void main(String[] args) {
        ShareResource resource = new ShareResource();

        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                resource.print5();
            }
        },"AA").start();

        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                resource.print10();
            }
        },"BB").start();

        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                resource.print15();
            }
        },"CC").start();
    }
}


class ShareResource{
    private int num = 1;
    private Lock lock = new ReentrantLock();
    private Condition condition1 = lock.newCondition();
    private Condition condition2 = lock.newCondition();
    private Condition condition3 = lock.newCondition();

    public void print5(){
        lock.lock();
        try {
            while (num != 1){
                condition1.await();
            }
            for (int i = 0; i < 5; i++) {
                System.out.println(Thread.currentThread().getName()+"\t "+i);
            }
            num = 2;
            condition2.signal();
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            lock.unlock();
        }
    }

    public void print10(){
        lock.lock();
        try {
            while (num != 2){
                condition2.await();
            }
            for (int i = 0; i < 10; i++) {
                System.out.println(Thread.currentThread().getName()+"\t "+i);
            }
            num = 3;
            condition3.signal();
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            lock.unlock();
        }
    }

    public void print15(){

        lock.lock();
        try {
            while (num != 3){
                try {
                    TimeUnit.SECONDS.sleep(4);} catch (InterruptedException e) {e.printStackTrace();}
                condition3.await();
            }
            for (int i = 0; i < 15; i++) {
                System.out.println(Thread.currentThread().getName()+"\t "+i);
            }
            num = 1;
            condition1.signal();
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            lock.unlock();
        }

        lock.lock();
        try {

        }catch (Exception e){
            e.printStackTrace();
        }finally {
            lock.unlock();
        }


    }
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113

七、线程池（ThreadPoolExecutor理解）

为什么用线程池，优势

线程池做的工作主要是控制运行的线程的数量，处理过程中将任务放入队列，然后在线程创建后启动这些任务，如果线程数量超过了最大数量的线程排队等候，等其他线程执行完毕，再从队列中取出任务执行。

特点：线程复用、控制最大并发数、管理线程。

• 降低资源消耗，通过重复利用已创建的线程降低线程创建和销毁造成的消耗。

• 提高响应速度，当任务到达时，任务可以不需要等到线程创建就能立即执行。

• 提高线程管理性，线程是稀缺资源，如果无限制创建，不仅会消耗系统资源，还会降低系统的稳定性，使用线程池可以进行统一分配调优和监控。

线程池如何使用

• 架构说明
  Java中线程池是通过Executor框架来实现，该框架中用到了Executor，Executors，ExecutorService，ThreadPoolExecutor这几个类。

• 编码实现

  • Executors.newScheduledThreadPool()

  • Executors.newWorkStealingpool(int) ----->java8新出

  • Executors.newFixedThreadPool(int) ----->执行长期的任务，性能好很多。

        /**
         * Creates a thread pool that reuses a fixed number of threads
         * operating off a shared unbounded queue.  At any point, at most
         * {@code nThreads} threads will be active processing tasks.
         * If additional tasks are submitted when all threads are active,
         * they will wait in the queue until a thread is available.
         * If any thread terminates due to a failure during execution
         * prior to shutdown, a new one will take its place if needed to
         * execute subsequent tasks.  The threads in the pool will exist
         * until it is explicitly {@link ExecutorService#shutdown shutdown}.
         *
         * @param nThreads the number of threads in the pool
         * @return the newly created thread pool
         * @throws IllegalArgumentException if {@code nThreads <= 0}
         */
        public static ExecutorService newFixedThreadPool(int nThreads) {
            return new ThreadPoolExecutor(nThreads, nThreads,
                                          0L, TimeUnit.MILLISECONDS,
                                          new LinkedBlockingQueue<Runnable>());
        }
    1
    2
    3
    4
    5
    6
    7
    8
    9
    10
    11
    12
    13
    14
    15
    16
    17
    18
    19
    20

    特点：

  1. 创建一个固定长度的线程池，可控制线程最大并发数，超出的线程会在队列中等待。
  2. newFixedThreadPool创建线程池corePoolSize和maximumPoolSize值是相等的，它使用LinkedBlockingQueue。

  • Executors.newSingleThreadExecutor() ----->一个任务一个任务执行的场景

        /**
         * Creates an Executor that uses a single worker thread operating
         * off an unbounded queue. (Note however that if this single
         * thread terminates due to a failure during execution prior to
         * shutdown, a new one will take its place if needed to execute
         * subsequent tasks.)  Tasks are guaranteed to execute
         * sequentially, and no more than one task will be active at any
         * given time. Unlike the otherwise equivalent
         * {@code newFixedThreadPool(1)} the returned executor is
         * guaranteed not to be reconfigurable to use additional threads.
         *
         * @return the newly created single-threaded Executor
         */
        public static ExecutorService newSingleThreadExecutor() {
            return new FinalizableDelegatedExecutorService
                (new ThreadPoolExecutor(1, 1,
                                        0L, TimeUnit.MILLISECONDS,
                                      new LinkedBlockingQueue<Runnable>()));
        }
    1
    2
    3
    4
    5
    6
    7
    8
    9
    10
    11
    12
    13
    14
    15
    16
    17
    18
    19

  
    > 特点：
    >
    > 1. 创建只有一个线程的线程池，它只会用唯一的工作线程来执行任务，保证所有任务按照指定顺序执行。
    > 2. newSingleThreadExecutor将corePoolSize和maximumPoolSize值都是 1 ，它使用**LinkedBlockingQueue**。
  
  * Executors.newCachedTheadPool() ----->执行很多短期异步的小程序或者负责较轻的服务器。
  
    ```java
        /**
         * Creates a thread pool that creates new threads as needed, but
         * will reuse previously constructed threads when they are
         * available.  These pools will typically improve the performance
         * of programs that execute many short-lived asynchronous tasks.
         * Calls to {@code execute} will reuse previously constructed
         * threads if available. If no existing thread is available, a new
         * thread will be created and added to the pool. Threads that have
         * not been used for sixty seconds are terminated and removed from
         * the cache. Thus, a pool that remains idle for long enough will
         * not consume any resources. Note that pools with similar
         * properties but different details (for example, timeout parameters)
         * may be created using {@link ThreadPoolExecutor} constructors.
         *
         * @return the newly created thread pool
         */
        public static ExecutorService newCachedThreadPool() {
            return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                          60L, TimeUnit.SECONDS,
                                          new SynchronousQueue());
        }
  1
  2
  3
  4
  5
  6
  7
  8
  9
  10
  11
  12
  13
  14
  15
  16
  17
  18
  19
  20
  21
  22
  23
  24
  25
  26
  27
  28
  29
  30

  特点：

  1. 创建一个可缓存线程池，如果线程池长度超过处理需要，可灵活回收空闲线程，若无可回收，则新建线程。
  2. newCachedThreadPool将corePoolSize设置为0，maximumPoolSize设置为Integer.MAX_VALUE，使用的SynchronousQueue，也就是说来了任务就创建线程运行，当线程空闲超过60秒，就销毁线程。

• ThreadPoolExecutor

线程池的几个重要参数介绍

ThreadPoolExecutor七大参数介绍：

1. corePoolSize：线程池中常驻核心线程数
2. maximumPoolSize：线程池能够容纳同时执行的最大线程数，此值必须大于1.
3. keepAliveTime：多余的空闲线程存活时间。
   当前线程池数量超过corePoolSize时，当空闲时间达到keepAliveTime值时，多余空闲线程会被销毁直到只剩下corePoolSize个线程为止。
4. unit：keepAliveTime的单位。
5. workQueue：任务队列，被提交但尚未执行的任务。
6. threadFactory：表示生成线程池中工作线程的线程工厂，用于创建线程一般用默认的即可。
7. handler：拒绝策略，表示当队列满了并且工作线程大于等于线程池的最大线程数（maximumPoolSize）时如何来

线程池底层工作原理

1. 在创建线程池后，等待提交过来的任务请求。
2. 当调用execute()方法添加一个请求任务时，线程池会做如下判断：
   2.1 如果正在运行的线程数量小于corePoolSize，那么马上创建线程运行这个任务。
   2.2 如果正在运行的线程数量大于或者等于corePoolSize，那么将这个任务放入队列。
   2.3 如果这个时候队列满了且正在运行的线程数量还小于maximumPoolSize，那么还是要创建非核心线程立刻运行这个任务。
   2.4 如果队列满了且正在运行的线程数量大于或等于maximumPoolSize，那么线程池会启动饱和和拒绝策略来执行。
3. 当一个线程完成任务之后，他会从队列中取下一个任务来执行。
4. 当一个线程无事可做超过一定的时间（keepAliveTime）时，线程池会判断：
   如果当前运行的线程数大于corePoolSize，那么这个线程会停掉。
   所以线程池的所有任务完成后他最终会收缩到corePoolSize大小。

线程池拒绝策略：

JDK内置的拒绝策略：(均实现了RejectedExecutionHandler接口)

1. AbortPolicy（默认）：直接抛出RejectedExecutionException异常组织系统正常运行。
2. CallerRunsPolicy：“调用者运行”一种调节机制，该策略既不会抛弃任务，也不会抛出异常，而是将某些任务回退到调用者，从而降低新任务流量。
3. DiscardOldestPolicy：抛弃队列中等待最久的任务，然后把当前任务加入队列中尝试再次提交当前任务。
4. DiscardPolicy：直接丢弃任务，不予处理也不抛异常。如果允许任务丢失，这是最好的一种方案。

八、死锁编码以及定位分析

• 产生死锁的原因
  死锁是指两个或者两个以上的进程在执行过程中，因争夺资源而造成的一种相互等待现象，若无外力干涉那他们都将无法推进下去，如果系统资源充足，进程的资源请求都能够得到满足，死锁出现的可能性比较低，否则就会因争夺有限的资源而陷入死锁。

• 代码:

  /**
   * 死锁是指两个或者两个以上的进程在执行过程中，因争夺资源而造成的一种相互等待现象
   *
   * @author shiwenquan
   * @Create 2020-12-24 16:53
   * @description
   */
  public class DeadLockDemo {
      public static void main(String[] args) {
          String lockA = "lockA";
          String lockB = "lockB";
  
          new Thread(new HoldLockThread(lockA,lockB),"AAA").start();
          new Thread(new HoldLockThread(lockB,lockA),"BBB").start();
      }
  
  }
  
  
  class HoldLockThread implements Runnable{
  
      private String lockA;
      private String lockB;
  
      public HoldLockThread(String lockA, String lockB) {
          this.lockA = lockA;
          this.lockB = lockB;
      }
  
      @Override
      public void run() {
          synchronized (lockA){
              System.out.println(Thread.currentThread().getName()+"\t 自己持有" + lockA + "\t 尝试获得" + lockB);
              try {
                  // 线程睡眠2秒钟
                  TimeUnit.SECONDS.sleep(2);
              } catch (InterruptedException e) {e.printStackTrace();}
  
              synchronized (lockB){
                  System.out.println(Thread.currentThread().getName()+"\t 自己持有" + lockB + "\t 尝试获得" + lockA);
              }
          }
      }
  }
  1
  2
  3
  4
  5
  6
  7
  8
  9
  10
  11
  12
  13
  14
  15
  16
  17
  18
  19
  20
  21
  22
  23
  24
  25
  26
  27
  28
  29
  30
  31
  32
  33
  34
  35
  36
  37
  38
  39
  40
  41
  42
  43
  44

• 解决：

  • jps命令定位进程号

    jps -l
    11488 org.jetbrains.idea.maven.server.RemoteMavenServer36
    16304 org.jetbrains.jps.cmdline.Launcher
    14452 org.study.guigu.DeadLockDemo
    12760
    13164 org.jetbrains.kotlin.daemon.KotlinCompileDaemon
    15596 sun.tools.jps.Jps
    1
    2
    3
    4
    5
    6
    7

  • jstack查看具体进程号确定是否是死锁。

    jstack 14452
    2020-12-24 17:04:55
    Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.231-b11 mixed mode):
    
    "DestroyJavaVM" #13 prio=5 os_prio=0 tid=0x0000000002d32800 nid=0x19f8 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "BBB" #12 prio=5 os_prio=0 tid=0x0000000018e81000 nid=0x4194 waiting for monitor entry [0x0000000019aff000]
       java.lang.Thread.State: BLOCKED (on object monitor)
            at org.study.guigu.HoldLockThread.run(DeadLockDemo.java:44)
            - waiting to lock <0x00000000d5dfd838> (a java.lang.String)
            - locked <0x00000000d5dfd870> (a java.lang.String)
            at java.lang.Thread.run(Thread.java:748)
    
    "AAA" #11 prio=5 os_prio=0 tid=0x0000000018e7e000 nid=0x3f9c waiting for monitor entry [0x00000000199ff000]
       java.lang.Thread.State: BLOCKED (on object monitor)
            at org.study.guigu.HoldLockThread.run(DeadLockDemo.java:44)
            - waiting to lock <0x00000000d5dfd870> (a java.lang.String)
            - locked <0x00000000d5dfd838> (a java.lang.String)
            at java.lang.Thread.run(Thread.java:748)
    
    "Service Thread" #10 daemon prio=9 os_prio=0 tid=0x0000000018dea000 nid=0x4354 runnable [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "C1 CompilerThread2" #9 daemon prio=9 os_prio=2 tid=0x0000000018d48800 nid=0x3644 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "C2 CompilerThread1" #8 daemon prio=9 os_prio=2 tid=0x0000000018d46000 nid=0x3108 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "C2 CompilerThread0" #7 daemon prio=9 os_prio=2 tid=0x0000000018d19000 nid=0x42d8 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "Monitor Ctrl-Break" #6 daemon prio=5 os_prio=0 tid=0x0000000018d51800 nid=0x3f74 runnable [0x00000000193fe000]
       java.lang.Thread.State: RUNNABLE
            at java.net.SocketInputStream.socketRead0(Native Method)
            at java.net.SocketInputStream.socketRead(SocketInputStream.java:116)
            at java.net.SocketInputStream.read(SocketInputStream.java:171)
            at java.net.SocketInputStream.read(SocketInputStream.java:141)
            at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:284)
            at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:326)
            at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:178)
            - locked <0x00000000d5d8ca88> (a java.io.InputStreamReader)
            at java.io.InputStreamReader.read(InputStreamReader.java:184)
            at java.io.BufferedReader.fill(BufferedReader.java:161)
            at java.io.BufferedReader.readLine(BufferedReader.java:324)
            - locked <0x00000000d5d8ca88> (a java.io.InputStreamReader)
            at java.io.BufferedReader.readLine(BufferedReader.java:389)
            at com.intellij.rt.execution.application.AppMainV2$1.run(AppMainV2.java:64)
    
    "Attach Listener" #5 daemon prio=5 os_prio=2 tid=0x00000000179af000 nid=0x3e98 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "Signal Dispatcher" #4 daemon prio=9 os_prio=2 tid=0x0000000018d08800 nid=0x4108 runnable [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "Finalizer" #3 daemon prio=8 os_prio=1 tid=0x0000000002e2b800 nid=0x416c in Object.wait() [0x0000000018cff000]
       java.lang.Thread.State: WAITING (on object monitor)
            at java.lang.Object.wait(Native Method)
            - waiting on <0x00000000d5c08ed8> (a java.lang.ref.ReferenceQueue$Lock)
            at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:144)
            - locked <0x00000000d5c08ed8> (a java.lang.ref.ReferenceQueue$Lock)
            at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:165)
            at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:216)
    
    "Reference Handler" #2 daemon prio=10 os_prio=2 tid=0x000000001798a000 nid=0x244 in Object.wait() [0x0000000018bff000]
       java.lang.Thread.State: WAITING (on object monitor)
            at java.lang.Object.wait(Native Method)
            - waiting on <0x00000000d5c06c00> (a java.lang.ref.Reference$Lock)
            at java.lang.Object.wait(Object.java:502)
            at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
            - locked <0x00000000d5c06c00> (a java.lang.ref.Reference$Lock)
            at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)
    
    "VM Thread" os_prio=2 tid=0x0000000017968000 nid=0x4310 runnable
    
    "GC task thread#0 (ParallelGC)" os_prio=0 tid=0x0000000002d48800 nid=0x3654 runnable
    
    "GC task thread#1 (ParallelGC)" os_prio=0 tid=0x0000000002d4a000 nid=0x608 runnable
    
    "GC task thread#2 (ParallelGC)" os_prio=0 tid=0x0000000002d4b800 nid=0xdec runnable
    
    "GC task thread#3 (ParallelGC)" os_prio=0 tid=0x0000000002d4e000 nid=0x2568 runnable
    
    "VM Periodic Task Thread" os_prio=2 tid=0x0000000018df0000 nid=0x42d4 waiting on condition
    
    JNI global references: 12
    
    
    Found one Java-level deadlock:
    =============================
    "BBB":
      waiting to lock monitor 0x0000000002e28768 (object 0x00000000d5dfd838, a java.lang.String),
      which is held by "AAA"
    "AAA":
      waiting to lock monitor 0x0000000002e2aff8 (object 0x00000000d5dfd870, a java.lang.String),
      which is held by "BBB"
    
    Java stack information for the threads listed above:
    ===================================================
    "BBB":
            at org.study.guigu.HoldLockThread.run(DeadLockDemo.java:44)
            - waiting to lock <0x00000000d5dfd838> (a java.lang.String)
            - locked <0x00000000d5dfd870> (a java.lang.String)
            at java.lang.Thread.run(Thread.java:748)
    "AAA":
            at org.study.guigu.HoldLockThread.run(DeadLockDemo.java:44)
            - waiting to lock <0x00000000d5dfd870> (a java.lang.String)
            - locked <0x00000000d5dfd838> (a java.lang.String)
            at java.lang.Thread.run(Thread.java:748)
    
    Found 1 deadlock.
    1
    2
    3
    4
    5
    6
    7
    8
    9
    10
    11
    12
    13
    14
    15
    16
    17
    18
    19
    20
    21
    22
    23
    24
    25
    26
    27
    28
    29
    30
    31
    32
    33
    34
    35
    36
    37
    38
    39
    40
    41
    42
    43
    44
    45
    46
    47
    48
    49
    50
    51
    52
    53
    54
    55
    56
    57
    58
    59
    60
    61
    62
    63
    64
    65
    66
    67
    68
    69
    70
    71
    72
    73
    74
    75
    76
    77
    78
    79
    80
    81
    82
    83
    84
    85
    86
    87
    88
    89
    90
    91
    92
    93
    94
    95
    96
    97
    98
    99
    100
    101
    102
    103
    104
    105
    106
    107
    108
    109
    110
    111
    112

九、JVM+GC

GC作用在方法区和堆中。

常见垃圾回收算法：

• 引用计数，JVM一般不采用这种方式。
• 复制，
• 标记清除，
• 标记清理，

JVM如何确定垃圾？是否知道GC Roots

什么是垃圾：内存中已经不再使用的的空间就是垃圾。

可以作为GC Roots的对象：

• 虚拟机栈（栈帧中的局部变量区，也叫做局部变量表）中引用的对象。
• 方法区中的类静态属性引用的对象。
• 方法区中常量引用的对象。
• 本地方法栈中JNI（Native方法）引用的对象。

JVM参数

• X参数

  • -Xint------解释执行
  • -Xcomp------第一次使用就编译成本地代码
  • -Xmixed------混合模式

• XX参数

  • Boolean类型

    • -XX：+或者 -某个属性

    • +表示开启

    • -表示关闭

      Case：

      1. 是否打印GC收集细节

         E:\workspace\study-guigu>jps -l
         1520 org.jetbrains.kotlin.daemon.KotlinCompileDaemon
         15144 org.study.guigu.GCRootsDemo
         15020 sun.tools.jps.Jps
         508 org.jetbrains.jps.cmdline.Launcher
         8316
         
         E:\workspace\study-guigu>jinfo -flag PrintGCDetails 15144
         -XX:-PrintGCDetails
         1
         2
         3
         4
         5
         6
         7
         8
         9

      2. 是否使用串行垃圾回收器

         E:\workspace\study-guigu>jps -l
         1520 org.jetbrains.kotlin.daemon.KotlinCompileDaemon
         240 org.jetbrains.jps.cmdline.Launcher
         8580 sun.tools.jps.Jps
         15048 org.study.guigu.GCRootsDemo
         8316
         
         E:\workspace\study-guigu>jinfo -flag UseSerialGC 15048
         -XX:-UseSerialGC
         
         1
         2
         3
         4
         5
         6
         7
         8
         9
         10

  • kv设置类型

    • -XX：属性key=属性值value

      Case：

      1. -XX:MetaspaceSize=128M

         E:\workspace\study-guigu>jps -l
         1520 org.jetbrains.kotlin.daemon.KotlinCompileDaemon
         240 org.jetbrains.jps.cmdline.Launcher
         15048 org.study.guigu.GCRootsDemo
         1260 sun.tools.jps.Jps
         8316
         
         E:\workspace\study-guigu>jinfo -flag MetaspaceSize 15048
         -XX:MetaspaceSize=21807104
         1
         2
         3
         4
         5
         6
         7
         8
         9

      2. -XX:MaxTenuringThreshold=15

         E:\workspace\study-guigu>jinfo -flag MaxTenuringThreshold 15048
         -XX:MaxTenuringThreshold=15
         1
         2

  • jinfo举例，如何查看当前运行程序的配置

    E:\workspace\study-guigu>jinfo -flags 15048
    Attaching to process ID 15048, please wait...
    Debugger attached successfully.
    Server compiler detected.
    JVM version is 25.231-b11
    Non-default VM flags: -XX:CICompilerCount=3 -XX:InitialHeapSize=134217728 -XX:MaxHeapSize=2126512128 -XX:MaxNewSize=708837376 -XX:MinHeapDeltaBytes=524288 -XX:NewSize=44
    564480 -XX:OldSize=89653248 -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseFastUnorderedTimeStamps -XX:-UseLargePagesIndividualAllocation -XX:+UseParalle
    lGC
    Command line:  -javaagent:D:\IntellijIDEA\IntelliJ IDEA 2019.2.4\lib\idea_rt.jar=55753:D:\IntellijIDEA\IntelliJ IDEA 2019.2.4\bin -Dfile.encoding=UTF-8
    1
    2
    3
    4
    5
    6
    7
    8
    9

  • 两个经典参数：-Xms和-Xmx

    -Xms等价于-XX:InitialHeapSize

    -Xmx等价于-XX:MaxHeapSize

JVM默认值

命令：java -XX:+PrintFlagsInitial

E:\workspace\study-guigu>java -XX:+PrintFlagsInitial
[Global flags]
     intx ActiveProcessorCount                      = -1                                  {product}
    uintx AdaptiveSizeDecrementScaleFactor          = 4                                   {product}
    uintx AdaptiveSizeMajorGCDecayTimeScale         = 10                                  {product}
    uintx AdaptiveSizePausePolicy                   = 0                                   {product}
    uintx AdaptiveSizePolicyCollectionCostMargin    = 50                                  {product}
    uintx AdaptiveSizePolicyInitializingSteps       = 20                                  {product}
    uintx AdaptiveSizePolicyOutputInterval          = 0                                   {product}
    uintx AdaptiveSizePolicyWeight                  = 10                                  {product}
    uintx AdaptiveSizeThroughPutPolicy              = 0                                   {product}
    uintx AdaptiveTimeWeight                        = 25                                  {product}
     bool AdjustConcurrency                         = false                               {product}
     bool AggressiveHeap                            = false                               {product}
     bool AggressiveOpts                            = false                               {product}
     intx AliasLevel                                = 3                                   {C2 product}
     bool AlignVector                               = true                                {C2 product}
     intx AllocateInstancePrefetchLines             = 1                                   {product}
     intx AllocatePrefetchDistance                  = -1                                  {product}
     intx AllocatePrefetchInstr                     = 0                                   {product}
     intx AllocatePrefetchLines                     = 3                                   {product}
     intx AllocatePrefetchStepSize                  = 16                                  {product}
     intx AllocatePrefetchStyle                     = 1                                   {product}
     bool AllowJNIEnvProxy                          = false                               {product}
     bool AllowNonVirtualCalls                      = false                               {product}
     bool AllowParallelDefineClass                  = false                               {product}
     bool AllowUserSignalHandlers                   = false                               {product}
     bool AlwaysActAsServerClassMachine             = false                               {product}
     bool AlwaysCompileLoopMethods                  = false                               {product}
     bool AlwaysLockClassLoader                     = false                               {product}
     bool AlwaysPreTouch                            = false                               {product}
     bool AlwaysRestoreFPU                          = false                               {product}
     bool AlwaysTenure                              = false                               {product}
     bool AssertOnSuspendWaitFailure                = false                               {product}
     bool AssumeMP                                  = false                               {product}
     intx AutoBoxCacheMax                           = 128                                 {C2 product}
    uintx AutoGCSelectPauseMillis                   = 5000                                {product}
     intx BCEATraceLevel                            = 0                                   {product}
     intx BackEdgeThreshold                         = 100000                              {pd product}
     bool BackgroundCompilation                     = true                                {pd product}
    uintx BaseFootPrintEstimate                     = 268435456                           {product}
     intx BiasedLockingBulkRebiasThreshold          = 20                                  {product}
     intx BiasedLockingBulkRevokeThreshold          = 40                                  {product}
     intx BiasedLockingDecayTime                    = 25000                               {product}
     intx BiasedLockingStartupDelay                 = 4000                                {product}
     bool BindGCTaskThreadsToCPUs                   = false                               {product}
     bool BlockLayoutByFrequency                    = true                                {C2 product}
     intx BlockLayoutMinDiamondPercentage           = 20                                  {C2 product}
     bool BlockLayoutRotateLoops                    = true                                {C2 product}
     bool BranchOnRegister                          = false                               {C2 product}
     bool BytecodeVerificationLocal                 = false                               {product}
     bool BytecodeVerificationRemote                = true                                {product}
     bool C1OptimizeVirtualCallProfiling            = true                                {C1 product}
     bool C1ProfileBranches                         = true                                {C1 product}
     bool C1ProfileCalls                            = true                                {C1 product}
     bool C1ProfileCheckcasts                       = true                                {C1 product}
     bool C1ProfileInlinedCalls                     = true                                {C1 product}
     bool C1ProfileVirtualCalls                     = true                                {C1 product}
     bool C1UpdateMethodData                        = true                                {C1 product}
     intx CICompilerCount                           = 2                                   {product}
     bool CICompilerCountPerCPU                     = false                               {product}
     bool CITime                                    = false                               {product}
     bool CMSAbortSemantics                         = false                               {product}
    uintx CMSAbortablePrecleanMinWorkPerIteration   = 100                                 {product}
     intx CMSAbortablePrecleanWaitMillis            = 100                                 {manageable}
    uintx CMSBitMapYieldQuantum                     = 10485760                            {product}
    uintx CMSBootstrapOccupancy                     = 50                                  {product}
     bool CMSClassUnloadingEnabled                  = true                                {product}
    uintx CMSClassUnloadingMaxInterval              = 0                                   {product}
     bool CMSCleanOnEnter                           = true                                {product}
     bool CMSCompactWhenClearAllSoftRefs            = true                                {product}
    uintx CMSConcMarkMultiple                       = 32                                  {product}
     bool CMSConcurrentMTEnabled                    = true                                {product}
    uintx CMSCoordinatorYieldSleepCount             = 10                                  {product}
     bool CMSDumpAtPromotionFailure                 = false                               {product}
     bool CMSEdenChunksRecordAlways                 = true                                {product}
    uintx CMSExpAvgFactor                           = 50                                  {product}
     bool CMSExtrapolateSweep                       = false                               {product}
    uintx CMSFullGCsBeforeCompaction                = 0                                   {product}
    uintx CMSIncrementalDutyCycle                   = 10                                  {product}
    uintx CMSIncrementalDutyCycleMin                = 0                                   {product}
     bool CMSIncrementalMode                        = false                               {product}
    uintx CMSIncrementalOffset                      = 0                                   {product}
     bool CMSIncrementalPacing                      = true                                {product}
    uintx CMSIncrementalSafetyFactor                = 10                                  {product}
    uintx CMSIndexedFreeListReplenish               = 4                                   {product}
     intx CMSInitiatingOccupancyFraction            = -1                                  {product}
    uintx CMSIsTooFullPercentage                    = 98                                  {product}
   double CMSLargeCoalSurplusPercent                = 0.950000                            {product}
   double CMSLargeSplitSurplusPercent               = 1.000000                            {product}
     bool CMSLoopWarn                               = false                               {product}
    uintx CMSMaxAbortablePrecleanLoops              = 0                                   {product}
     intx CMSMaxAbortablePrecleanTime               = 5000                                {product}
    uintx CMSOldPLABMax                             = 1024                                {product}
    uintx CMSOldPLABMin                             = 16                                  {product}
    uintx CMSOldPLABNumRefills                      = 4                                   {product}
    uintx CMSOldPLABReactivityFactor                = 2                                   {product}
     bool CMSOldPLABResizeQuicker                   = false                               {product}
    uintx CMSOldPLABToleranceFactor                 = 4                                   {product}
     bool CMSPLABRecordAlways                       = true                                {product}
    uintx CMSParPromoteBlocksToClaim                = 16                                  {product}
     bool CMSParallelInitialMarkEnabled             = true                                {product}
     bool CMSParallelRemarkEnabled                  = true                                {product}
     bool CMSParallelSurvivorRemarkEnabled          = true                                {product}
    uintx CMSPrecleanDenominator                    = 3                                   {product}
    uintx CMSPrecleanIter                           = 3                                   {product}
    uintx CMSPrecleanNumerator                      = 2                                   {product}
     bool CMSPrecleanRefLists1                      = true                                {product}
     bool CMSPrecleanRefLists2                      = false                               {product}
     bool CMSPrecleanSurvivors1                     = false                               {product}
     bool CMSPrecleanSurvivors2                     = true                                {product}
    uintx CMSPrecleanThreshold                      = 1000                                {product}
     bool CMSPrecleaningEnabled                     = true                                {product}
     bool CMSPrintChunksInDump                      = false                               {product}
     bool CMSPrintEdenSurvivorChunks                = false                               {product}
     bool CMSPrintObjectsInDump                     = false                               {product}
    uintx CMSRemarkVerifyVariant                    = 1                                   {product}
     bool CMSReplenishIntermediate                  = true                                {product}
    uintx CMSRescanMultiple                         = 32                                  {product}
    uintx CMSSamplingGrain                          = 16384                               {product}
     bool CMSScavengeBeforeRemark                   = false                               {product}
    uintx CMSScheduleRemarkEdenPenetration          = 50                                  {product}
    uintx CMSScheduleRemarkEdenSizeThreshold        = 2097152                             {product}
    uintx CMSScheduleRemarkSamplingRatio            = 5                                   {product}
   double CMSSmallCoalSurplusPercent                = 1.050000                            {product}
   double CMSSmallSplitSurplusPercent               = 1.100000                            {product}
     bool CMSSplitIndexedFreeListBlocks             = true                                {product}
     intx CMSTriggerInterval                        = -1                                  {manageable}
    uintx CMSTriggerRatio                           = 80                                  {product}
     intx CMSWaitDuration                           = 2000                                {manageable}
    uintx CMSWorkQueueDrainThreshold                = 10                                  {product}
     bool CMSYield                                  = true                                {product}
    uintx CMSYieldSleepCount                        = 0                                   {product}
    uintx CMSYoungGenPerWorker                      = 67108864                            {pd product}
    uintx CMS_FLSPadding                            = 1                                   {product}
    uintx CMS_FLSWeight                             = 75                                  {product}
    uintx CMS_SweepPadding                          = 1                                   {product}
    uintx CMS_SweepTimerThresholdMillis             = 10                                  {product}
    uintx CMS_SweepWeight                           = 75                                  {product}
     bool CheckEndorsedAndExtDirs                   = false                               {product}
     bool CheckJNICalls                             = false                               {product}
     bool ClassUnloading                            = true                                {product}
     bool ClassUnloadingWithConcurrentMark          = true                                {product}
     intx ClearFPUAtPark                            = 0                                   {product}
     bool ClipInlining                              = true                                {product}
    uintx CodeCacheExpansionSize                    = 65536                               {pd product}
    uintx CodeCacheMinimumFreeSpace                 = 512000                              {product}
     bool CollectGen0First                          = false                               {product}
     bool CompactFields                             = true                                {product}
     intx CompilationPolicyChoice                   = 0                                   {product}
ccstrlist CompileCommand                            =                                     {product}
    ccstr CompileCommandFile                        =                                     {product}
ccstrlist CompileOnly                               =                                     {product}
     intx CompileThreshold                          = 10000                               {pd product}
     bool CompilerThreadHintNoPreempt               = true                                {product}
     intx CompilerThreadPriority                    = -1                                  {product}
     intx CompilerThreadStackSize                   = 0                                   {pd product}
    uintx CompressedClassSpaceSize                  = 1073741824                          {product}
    uintx ConcGCThreads                             = 0                                   {product}
     intx ConditionalMoveLimit                      = 3                                   {C2 pd product}
     intx ContendedPaddingWidth                     = 128                                 {product}
     bool ConvertSleepToYield                       = true                                {pd product}
     bool ConvertYieldToSleep                       = false                               {product}
     bool CrashOnOutOfMemoryError                   = false                               {product}
     bool CreateMinidumpOnCrash                     = false                               {product}
     bool CriticalJNINatives                        = true                                {product}
     bool DTraceAllocProbes                         = false                               {product}
     bool DTraceMethodProbes                        = false                               {product}
     bool DTraceMonitorProbes                       = false                               {product}
     bool Debugging                                 = false                               {product}
    uintx DefaultMaxRAMFraction                     = 4                                   {product}
     intx DefaultThreadPriority                     = -1                                  {product}
     intx DeferPollingPageLoopCount                 = -1                                  {product}
     intx DeferThrSuspendLoopCount                  = 4000                                {product}
     bool DeoptimizeRandom                          = false                               {product}
     bool DisableAttachMechanism                    = false                               {product}
     bool DisableExplicitGC                         = false                               {product}
     bool DisplayVMOutputToStderr                   = false                               {product}
     bool DisplayVMOutputToStdout                   = false                               {product}
     bool DoEscapeAnalysis                          = true                                {C2 product}
     bool DontCompileHugeMethods                    = true                                {product}
     bool DontYieldALot                             = false                               {pd product}
    ccstr DumpLoadedClassList                       =                                     {product}
     bool DumpReplayDataOnError                     = true                                {product}
     bool DumpSharedSpaces                          = false                               {product}
     bool EagerXrunInit                             = false                               {product}
     intx EliminateAllocationArraySizeLimit         = 64                                  {C2 product}
     bool EliminateAllocations                      = true                                {C2 product}
     bool EliminateAutoBox                          = true                                {C2 product}
     bool EliminateLocks                            = true                                {C2 product}
     bool EliminateNestedLocks                      = true                                {C2 product}
     intx EmitSync                                  = 0                                   {product}
     bool EnableContended                           = true                                {product}
     bool EnableResourceManagementTLABCache         = true                                {product}
     bool EnableSharedLookupCache                   = true                                {product}
     bool EnableTracing                             = false                               {product}
    uintx ErgoHeapSizeLimit                         = 0                                   {product}
    ccstr ErrorFile                                 =                                     {product}
    ccstr ErrorReportServer                         =                                     {product}
   double EscapeAnalysisTimeout                     = 20.000000                           {C2 product}
     bool EstimateArgEscape                         = true                                {product}
     bool ExitOnOutOfMemoryError                    = false                               {product}
     bool ExplicitGCInvokesConcurrent               = false                               {product}
     bool ExplicitGCInvokesConcurrentAndUnloadsClasses  = false                               {product}
     bool ExtendedDTraceProbes                      = false                               {product}
    ccstr ExtraSharedClassListFile                  =                                     {product}
     bool FLSAlwaysCoalesceLarge                    = false                               {product}
    uintx FLSCoalescePolicy                         = 2                                   {product}
   double FLSLargestBlockCoalesceProximity          = 0.990000                            {product}
     bool FailOverToOldVerifier                     = true                                {product}
     bool FastTLABRefill                            = true                                {product}
     intx FenceInstruction                          = 0                                   {ARCH product}
     intx FieldsAllocationStyle                     = 1                                   {product}
     bool FilterSpuriousWakeups                     = true                                {product}
    ccstr FlightRecorderOptions                     =                                     {product}
     bool ForceNUMA                                 = false                               {product}
     bool ForceTimeHighResolution                   = false                               {product}
     intx FreqInlineSize                            = 325                                 {pd product}
   double G1ConcMarkStepDurationMillis              = 10.000000                           {product}
    uintx G1ConcRSHotCardLimit                      = 4                                   {product}
    uintx G1ConcRSLogCacheSize                      = 10                                  {product}
     intx G1ConcRefinementGreenZone                 = 0                                   {product}
     intx G1ConcRefinementRedZone                   = 0                                   {product}
     intx G1ConcRefinementServiceIntervalMillis     = 300                                 {product}
    uintx G1ConcRefinementThreads                   = 0                                   {product}
     intx G1ConcRefinementThresholdStep             = 0                                   {product}
     intx G1ConcRefinementYellowZone                = 0                                   {product}
    uintx G1ConfidencePercent                       = 50                                  {product}
    uintx G1HeapRegionSize                          = 0                                   {product}
    uintx G1HeapWastePercent                        = 5                                   {product}
    uintx G1MixedGCCountTarget                      = 8                                   {product}
     intx G1RSetRegionEntries                       = 0                                   {product}
    uintx G1RSetScanBlockSize                       = 64                                  {product}
     intx G1RSetSparseRegionEntries                 = 0                                   {product}
     intx G1RSetUpdatingPauseTimePercent            = 10                                  {product}
     intx G1RefProcDrainInterval                    = 10                                  {product}
    uintx G1ReservePercent                          = 10                                  {product}
    uintx G1SATBBufferEnqueueingThresholdPercent    = 60                                  {product}
     intx G1SATBBufferSize                          = 1024                                {product}
     intx G1UpdateBufferSize                        = 256                                 {product}
     bool G1UseAdaptiveConcRefinement               = true                                {product}
    uintx GCDrainStackTargetSize                    = 64                                  {product}
    uintx GCHeapFreeLimit                           = 2                                   {product}
    uintx GCLockerEdenExpansionPercent              = 5                                   {product}
     bool GCLockerInvokesConcurrent                 = false                               {product}
    uintx GCLogFileSize                             = 8192                                {product}
    uintx GCPauseIntervalMillis                     = 0                                   {product}
    uintx GCTaskTimeStampEntries                    = 200                                 {product}
    uintx GCTimeLimit                               = 98                                  {product}
    uintx GCTimeRatio                               = 99                                  {product}
    uintx HeapBaseMinAddress                        = 2147483648                          {pd product}
     bool HeapDumpAfterFullGC                       = false                               {manageable}
     bool HeapDumpBeforeFullGC                      = false                               {manageable}
     bool HeapDumpOnOutOfMemoryError                = false                               {manageable}
    ccstr HeapDumpPath                              =                                     {manageable}
    uintx HeapFirstMaximumCompactionCount           = 3                                   {product}
    uintx HeapMaximumCompactionInterval             = 20                                  {product}
    uintx HeapSizePerGCThread                       = 87241520                            {product}
     bool IgnoreEmptyClassPaths                     = false                               {product}
     bool IgnoreUnrecognizedVMOptions               = false                               {product}
    uintx IncreaseFirstTierCompileThresholdAt       = 50                                  {product}
     bool IncrementalInline                         = true                                {C2 product}
    uintx InitialBootClassLoaderMetaspaceSize       = 4194304                             {product}
    uintx InitialCodeCacheSize                      = 2555904                             {pd product}
    uintx InitialHeapSize                           = 0                                   {product}
    uintx InitialRAMFraction                        = 64                                  {product}
   double InitialRAMPercentage                      = 1.562500                            {product}
    uintx InitialSurvivorRatio                      = 8                                   {product}
    uintx InitialTenuringThreshold                  = 7                                   {product}
    uintx InitiatingHeapOccupancyPercent            = 45                                  {product}
     bool Inline                                    = true                                {product}
    ccstr InlineDataFile                            =                                     {product}
     intx InlineSmallCode                           = 1000                                {pd product}
     bool InlineSynchronizedMethods                 = true                                {C1 product}
     bool InsertMemBarAfterArraycopy                = true                                {C2 product}
     intx InteriorEntryAlignment                    = 16                                  {C2 pd product}
     intx InterpreterProfilePercentage              = 33                                  {product}
     bool JNIDetachReleasesMonitors                 = true                                {product}
     bool JavaMonitorsInStackTrace                  = true                                {product}
     intx JavaPriority10_To_OSPriority              = -1                                  {product}
     intx JavaPriority1_To_OSPriority               = -1                                  {product}
     intx JavaPriority2_To_OSPriority               = -1                                  {product}
     intx JavaPriority3_To_OSPriority               = -1                                  {product}
     intx JavaPriority4_To_OSPriority               = -1                                  {product}
     intx JavaPriority5_To_OSPriority               = -1                                  {product}
     intx JavaPriority6_To_OSPriority               = -1                                  {product}
     intx JavaPriority7_To_OSPriority               = -1                                  {product}
     intx JavaPriority8_To_OSPriority               = -1                                  {product}
     intx JavaPriority9_To_OSPriority               = -1                                  {product}
     bool LIRFillDelaySlots                         = false                               {C1 pd product}
    uintx LargePageHeapSizeThreshold                = 134217728                           {product}
    uintx LargePageSizeInBytes                      = 0                                   {product}
     bool LazyBootClassLoader                       = true                                {product}
     intx LiveNodeCountInliningCutoff               = 40000                               {C2 product}
     bool LogCommercialFeatures                     = false                               {product}
     intx LoopMaxUnroll                             = 16                                  {C2 product}
     intx LoopOptsCount                             = 43                                  {C2 product}
     intx LoopUnrollLimit                           = 60                                  {C2 pd product}
     intx LoopUnrollMin                             = 4                                   {C2 product}
     bool LoopUnswitching                           = true                                {C2 product}
     bool ManagementServer                          = false                               {product}
    uintx MarkStackSize                             = 4194304                             {product}
    uintx MarkStackSizeMax                          = 536870912                           {product}
    uintx MarkSweepAlwaysCompactCount               = 4                                   {product}
    uintx MarkSweepDeadRatio                        = 5                                   {product}
     intx MaxBCEAEstimateLevel                      = 5                                   {product}
     intx MaxBCEAEstimateSize                       = 150                                 {product}
    uintx MaxDirectMemorySize                       = 0                                   {product}
     bool MaxFDLimit                                = true                                {product}
    uintx MaxGCMinorPauseMillis                     = 4294967295                          {product}
    uintx MaxGCPauseMillis                          = 4294967295                          {product}
    uintx MaxHeapFreeRatio                          = 70                                  {manageable}
    uintx MaxHeapSize                               = 130862280                           {product}
     intx MaxInlineLevel                            = 9                                   {product}
     intx MaxInlineSize                             = 35                                  {product}
     intx MaxJNILocalCapacity                       = 65536                               {product}
     intx MaxJavaStackTraceDepth                    = 1024                                {product}
     intx MaxJumpTableSize                          = 65000                               {C2 product}
     intx MaxJumpTableSparseness                    = 5                                   {C2 product}
     intx MaxLabelRootDepth                         = 1100                                {C2 product}
     intx MaxLoopPad                                = 15                                  {C2 product}
    uintx MaxMetaspaceExpansion                     = 5452592                             {product}
    uintx MaxMetaspaceFreeRatio                     = 70                                  {product}
    uintx MaxMetaspaceSize                          = 4294967295                          {product}
    uintx MaxNewSize                                = 4294967295                          {product}
     intx MaxNodeLimit                              = 80000                               {C2 product}
 uint64_t MaxRAM                                    = 0                                   {pd product}
    uintx MaxRAMFraction                            = 4                                   {product}
   double MaxRAMPercentage                          = 25.000000                           {product}
     intx MaxRecursiveInlineLevel                   = 1                                   {product}
    uintx MaxTenuringThreshold                      = 15                                  {product}
     intx MaxTrivialSize                            = 6                                   {product}
     intx MaxVectorSize                             = 32                                  {C2 product}
    uintx MetaspaceSize                             = 21810376                            {pd product}
     bool MethodFlushing                            = true                                {product}
    uintx MinHeapDeltaBytes                         = 170392                              {product}
    uintx MinHeapFreeRatio                          = 40                                  {manageable}
     intx MinInliningThreshold                      = 250                                 {product}
     intx MinJumpTableSize                          = 10                                  {C2 pd product}
    uintx MinMetaspaceExpansion                     = 340784                              {product}
    uintx MinMetaspaceFreeRatio                     = 40                                  {product}
    uintx MinRAMFraction                            = 2                                   {product}
   double MinRAMPercentage                          = 50.000000                           {product}
    uintx MinSurvivorRatio                          = 3                                   {product}
    uintx MinTLABSize                               = 2048                                {product}
     intx MonitorBound                              = 0                                   {product}
     bool MonitorInUseLists                         = false                               {product}
     intx MultiArrayExpandLimit                     = 6                                   {C2 product}
     bool MustCallLoadClassInternal                 = false                               {product}
    uintx NUMAChunkResizeWeight                     = 20                                  {product}
    uintx NUMAInterleaveGranularity                 = 2097152                             {product}
    uintx NUMAPageScanRate                          = 256                                 {product}
    uintx NUMASpaceResizeRate                       = 1073741824                          {product}
     bool NUMAStats                                 = false                               {product}
    ccstr NativeMemoryTracking                      = off                                 {product}
     bool NeedsDeoptSuspend                         = false                               {pd product}
     bool NeverActAsServerClassMachine              = false                               {pd product}
     bool NeverTenure                               = false                               {product}
    uintx NewRatio                                  = 2                                   {product}
    uintx NewSize                                   = 1363144                             {product}
    uintx NewSizeThreadIncrease                     = 5320                                {pd product}
     intx NmethodSweepActivity                      = 10                                  {product}
     intx NmethodSweepCheckInterval                 = 5                                   {product}
     intx NmethodSweepFraction                      = 16                                  {product}
     intx NodeLimitFudgeFactor                      = 2000                                {C2 product}
    uintx NumberOfGCLogFiles                        = 0                                   {product}
     intx NumberOfLoopInstrToAlign                  = 4                                   {C2 product}
     intx ObjectAlignmentInBytes                    = 8                                   {lp64_product}
    uintx OldPLABSize                               = 1024                                {product}
    uintx OldPLABWeight                             = 50                                  {product}
    uintx OldSize                                   = 5452592                             {product}
     bool OmitStackTraceInFastThrow                 = true                                {product}
ccstrlist OnError                                   =                                     {product}
ccstrlist OnOutOfMemoryError                        =                                     {product}
     intx OnStackReplacePercentage                  = 140                                 {pd product}
     bool OptimizeFill                              = true                                {C2 product}
     bool OptimizePtrCompare                        = true                                {C2 product}
     bool OptimizeStringConcat                      = true                                {C2 product}
     bool OptoBundling                              = false                               {C2 pd product}
     intx OptoLoopAlignment                         = 16                                  {pd product}
     bool OptoScheduling                            = false                               {C2 pd product}
    uintx PLABWeight                                = 75                                  {product}
     bool PSChunkLargeArrays                        = true                                {product}
     intx ParGCArrayScanChunk                       = 50                                  {product}
    uintx ParGCDesiredObjsFromOverflowList          = 20                                  {product}
     bool ParGCTrimOverflow                         = true                                {product}
     bool ParGCUseLocalOverflow                     = false                               {product}
    uintx ParallelGCBufferWastePct                  = 10                                  {product}
    uintx ParallelGCThreads                         = 0                                   {product}
     bool ParallelGCVerbose                         = false                               {product}
    uintx ParallelOldDeadWoodLimiterMean            = 50                                  {product}
    uintx ParallelOldDeadWoodLimiterStdDev          = 80                                  {product}
     bool ParallelRefProcBalancingEnabled           = true                                {product}
     bool ParallelRefProcEnabled                    = false                               {product}
     bool PartialPeelAtUnsignedTests                = true                                {C2 product}
     bool PartialPeelLoop                           = true                                {C2 product}
     intx PartialPeelNewPhiDelta                    = 0                                   {C2 product}
    uintx PausePadding                              = 1                                   {product}
     intx PerBytecodeRecompilationCutoff            = 200                                 {product}
     intx PerBytecodeTrapLimit                      = 4                                   {product}
     intx PerMethodRecompilationCutoff              = 400                                 {product}
     intx PerMethodTrapLimit                        = 100                                 {product}
     bool PerfAllowAtExitRegistration               = false                               {product}
     bool PerfBypassFileSystemCheck                 = false                               {product}
     intx PerfDataMemorySize                        = 32768                               {product}
     intx PerfDataSamplingInterval                  = 50                                  {product}
    ccstr PerfDataSaveFile                          =                                     {product}
     bool PerfDataSaveToFile                        = false                               {product}
     bool PerfDisableSharedMem                      = false                               {product}
     intx PerfMaxStringConstLength                  = 1024                                {product}
     intx PreInflateSpin                            = 10                                  {pd product}
     bool PreferInterpreterNativeStubs              = false                               {pd product}
     intx PrefetchCopyIntervalInBytes               = -1                                  {product}
     intx PrefetchFieldsAhead                       = -1                                  {product}
     intx PrefetchScanIntervalInBytes               = -1                                  {product}
     bool PreserveAllAnnotations                    = false                               {product}
     bool PreserveFramePointer                      = false                               {pd product}
    uintx PretenureSizeThreshold                    = 0                                   {product}
     bool PrintAdaptiveSizePolicy                   = false                               {product}
     bool PrintCMSInitiationStatistics              = false                               {product}
     intx PrintCMSStatistics                        = 0                                   {product}
     bool PrintClassHistogram                       = false                               {manageable}
     bool PrintClassHistogramAfterFullGC            = false                               {manageable}
     bool PrintClassHistogramBeforeFullGC           = false                               {manageable}
     bool PrintCodeCache                            = false                               {product}
     bool PrintCodeCacheOnCompilation               = false                               {product}
     bool PrintCommandLineFlags                     = false                               {product}
     bool PrintCompilation                          = false                               {product}
     bool PrintConcurrentLocks                      = false                               {manageable}
     intx PrintFLSCensus                            = 0                                   {product}
     intx PrintFLSStatistics                        = 0                                   {product}
     bool PrintFlagsFinal                           = false                               {product}
     bool PrintFlagsInitial                         = false                               {product}
     bool PrintGC                                   = false                               {manageable}
     bool PrintGCApplicationConcurrentTime          = false                               {product}
     bool PrintGCApplicationStoppedTime             = false                               {product}
     bool PrintGCCause                              = true                                {product}
     bool PrintGCDateStamps                         = false                               {manageable}
     bool PrintGCDetails                            = false                               {manageable}
     bool PrintGCID                                 = false                               {manageable}
     bool PrintGCTaskTimeStamps                     = false                               {product}
     bool PrintGCTimeStamps                         = false                               {manageable}
     bool PrintHeapAtGC                             = false                               {product rw}
     bool PrintHeapAtGCExtended                     = false                               {product rw}
     bool PrintHeapAtSIGBREAK                       = true                                {product}
     bool PrintJNIGCStalls                          = false                               {product}
     bool PrintJNIResolving                         = false                               {product}
     bool PrintOldPLAB                              = false                               {product}
     bool PrintOopAddress                           = false                               {product}
     bool PrintPLAB                                 = false                               {product}
     bool PrintParallelOldGCPhaseTimes              = false                               {product}
     bool PrintPromotionFailure                     = false                               {product}
     bool PrintReferenceGC                          = false                               {product}
     bool PrintSafepointStatistics                  = false                               {product}
     intx PrintSafepointStatisticsCount             = 300                                 {product}
     intx PrintSafepointStatisticsTimeout           = -1                                  {product}
     bool PrintSharedArchiveAndExit                 = false                               {product}
     bool PrintSharedDictionary                     = false                               {product}
     bool PrintSharedSpaces                         = false                               {product}
     bool PrintStringDeduplicationStatistics        = false                               {product}
     bool PrintStringTableStatistics                = false                               {product}
     bool PrintTLAB                                 = false                               {product}
     bool PrintTenuringDistribution                 = false                               {product}
     bool PrintTieredEvents                         = false                               {product}
     bool PrintVMOptions                            = false                               {product}
     bool PrintVMQWaitTime                          = false                               {product}
     bool PrintWarnings                             = true                                {product}
    uintx ProcessDistributionStride                 = 4                                   {product}
     bool ProfileInterpreter                        = true                                {pd product}
     bool ProfileIntervals                          = false                               {product}
     intx ProfileIntervalsTicks                     = 100                                 {product}
     intx ProfileMaturityPercentage                 = 20                                  {product}
     bool ProfileVM                                 = false                               {product}
     bool ProfilerPrintByteCodeStatistics           = false                               {product}
     bool ProfilerRecordPC                          = false                               {product}
    uintx PromotedPadding                           = 3                                   {product}
    uintx QueuedAllocationWarningCount              = 0                                   {product}
    uintx RTMRetryCount                             = 5                                   {ARCH product}
     bool RangeCheckElimination                     = true                                {product}
     intx ReadPrefetchInstr                         = 0                                   {ARCH product}
     bool ReassociateInvariants                     = true                                {C2 product}
     bool ReduceBulkZeroing                         = true                                {C2 product}
     bool ReduceFieldZeroing                        = true                                {C2 product}
     bool ReduceInitialCardMarks                    = true                                {C2 product}
     bool ReduceSignalUsage                         = false                               {product}
     intx RefDiscoveryPolicy                        = 0                                   {product}
     bool ReflectionWrapResolutionErrors            = true                                {product}
     bool RegisterFinalizersAtInit                  = true                                {product}
     bool RelaxAccessControlCheck                   = false                               {product}
    ccstr ReplayDataFile                            =                                     {product}
     bool RequireSharedSpaces                       = false                               {product}
    uintx ReservedCodeCacheSize                     = 50331648                            {pd product}
     bool ResizeOldPLAB                             = true                                {product}
     bool ResizePLAB                                = true                                {product}
     bool ResizeTLAB                                = true                                {pd product}
     bool RestoreMXCSROnJNICalls                    = false                               {product}
     bool RestrictContended                         = true                                {product}
     bool RewriteBytecodes                          = true                                {pd product}
     bool RewriteFrequentPairs                      = true                                {pd product}
     intx SafepointPollOffset                       = 256                                 {C1 pd product}
     intx SafepointSpinBeforeYield                  = 2000                                {product}
     bool SafepointTimeout                          = false                               {product}
     intx SafepointTimeoutDelay                     = 10000                               {product}
     bool ScavengeBeforeFullGC                      = true                                {product}
     intx SelfDestructTimer                         = 0                                   {product}
    uintx SharedBaseAddress                         = 0                                   {product}
    ccstr SharedClassListFile                       =                                     {product}
    uintx SharedMiscCodeSize                        = 122880                              {product}
    uintx SharedMiscDataSize                        = 4194304                             {product}
    uintx SharedReadOnlySize                        = 16777216                            {product}
    uintx SharedReadWriteSize                       = 16777216                            {product}
     bool ShowMessageBoxOnError                     = false                               {product}
     intx SoftRefLRUPolicyMSPerMB                   = 1000                                {product}
     bool SpecialEncodeISOArray                     = true                                {C2 product}
     bool SplitIfBlocks                             = true                                {C2 product}
     intx StackRedPages                             = 1                                   {pd product}
     intx StackShadowPages                          = 6                                   {pd product}
     bool StackTraceInThrowable                     = true                                {product}
     intx StackYellowPages                          = 3                                   {pd product}
     bool StartAttachListener                       = false                               {product}
     intx StarvationMonitorInterval                 = 200                                 {product}
     bool StressLdcRewrite                          = false                               {product}
    uintx StringDeduplicationAgeThreshold           = 3                                   {product}
    uintx StringTableSize                           = 60013                               {product}
     bool SuppressFatalErrorMessage                 = false                               {product}
    uintx SurvivorPadding                           = 3                                   {product}
    uintx SurvivorRatio                             = 8                                   {product}
     intx SuspendRetryCount                         = 50                                  {product}
     intx SuspendRetryDelay                         = 5                                   {product}
     intx SyncFlags                                 = 0                                   {product}
    ccstr SyncKnobs                                 =                                     {product}
     intx SyncVerbose                               = 0                                   {product}
    uintx TLABAllocationWeight                      = 35                                  {product}
    uintx TLABRefillWasteFraction                   = 64                                  {product}
    uintx TLABSize                                  = 0                                   {product}
     bool TLABStats                                 = true                                {product}
    uintx TLABWasteIncrement                        = 4                                   {product}
    uintx TLABWasteTargetPercent                    = 1                                   {product}
    uintx TargetPLABWastePct                        = 10                                  {product}
    uintx TargetSurvivorRatio                       = 50                                  {product}
    uintx TenuredGenerationSizeIncrement            = 20                                  {product}
    uintx TenuredGenerationSizeSupplement           = 80                                  {product}
    uintx TenuredGenerationSizeSupplementDecay      = 2                                   {product}
     intx ThreadPriorityPolicy                      = 0                                   {product}
     bool ThreadPriorityVerbose                     = false                               {product}
    uintx ThreadSafetyMargin                        = 52428800                            {product}
     intx ThreadStackSize                           = 0                                   {pd product}
    uintx ThresholdTolerance                        = 10                                  {product}
     intx Tier0BackedgeNotifyFreqLog                = 10                                  {product}
     intx Tier0InvokeNotifyFreqLog                  = 7                                   {product}
     intx Tier0ProfilingStartPercentage             = 200                                 {product}
     intx Tier23InlineeNotifyFreqLog                = 20                                  {product}
     intx Tier2BackEdgeThreshold                    = 0                                   {product}
     intx Tier2BackedgeNotifyFreqLog                = 14                                  {product}
     intx Tier2CompileThreshold                     = 0                                   {product}
     intx Tier2InvokeNotifyFreqLog                  = 11                                  {product}
     intx Tier3BackEdgeThreshold                    = 60000                               {product}
     intx Tier3BackedgeNotifyFreqLog                = 13                                  {product}
     intx Tier3CompileThreshold                     = 2000                                {product}
     intx Tier3DelayOff                             = 2                                   {product}
     intx Tier3DelayOn                              = 5                                   {product}
     intx Tier3InvocationThreshold                  = 200                                 {product}
     intx Tier3InvokeNotifyFreqLog                  = 10                                  {product}
     intx Tier3LoadFeedback                         = 5                                   {product}
     intx Tier3MinInvocationThreshold               = 100                                 {product}
     intx Tier4BackEdgeThreshold                    = 40000                               {product}
     intx Tier4CompileThreshold                     = 15000                               {product}
     intx Tier4InvocationThreshold                  = 5000                                {product}
     intx Tier4LoadFeedback                         = 3                                   {product}
     intx Tier4MinInvocationThreshold               = 600                                 {product}
     bool TieredCompilation                         = true                                {pd product}
     intx TieredCompileTaskTimeout                  = 50                                  {product}
     intx TieredRateUpdateMaxTime                   = 25                                  {product}
     intx TieredRateUpdateMinTime                   = 1                                   {product}
     intx TieredStopAtLevel                         = 4                                   {product}
     bool TimeLinearScan                            = false                               {C1 product}
     bool TraceBiasedLocking                        = false                               {product}
     bool TraceClassLoading                         = false                               {product rw}
     bool TraceClassLoadingPreorder                 = false                               {product}
     bool TraceClassPaths                           = false                               {product}
     bool TraceClassResolution                      = false                               {product}
     bool TraceClassUnloading                       = false                               {product rw}
     bool TraceDynamicGCThreads                     = false                               {product}
     bool TraceGen0Time                             = false                               {product}
     bool TraceGen1Time                             = false                               {product}
    ccstr TraceJVMTI                                =                                     {product}
     bool TraceLoaderConstraints                    = false                               {product rw}
     bool TraceMetadataHumongousAllocation          = false                               {product}
     bool TraceMonitorInflation                     = false                               {product}
     bool TraceParallelOldGCTasks                   = false                               {product}
     intx TraceRedefineClasses                      = 0                                   {product}
     bool TraceSafepointCleanupTime                 = false                               {product}
     bool TraceSharedLookupCache                    = false                               {product}
     bool TraceSuspendWaitFailures                  = false                               {product}
     intx TrackedInitializationLimit                = 50                                  {C2 product}
     bool TransmitErrorReport                       = false                               {product}
     bool TrapBasedNullChecks                       = false                               {pd product}
     bool TrapBasedRangeChecks                      = false                               {C2 pd product}
     intx TypeProfileArgsLimit                      = 2                                   {product}
    uintx TypeProfileLevel                          = 111                                 {pd product}
     intx TypeProfileMajorReceiverPercent           = 90                                  {C2 product}
     intx TypeProfileParmsLimit                     = 2                                   {product}
     intx TypeProfileWidth                          = 2                                   {product}
     intx UnguardOnExecutionViolation               = 0                                   {product}
     bool UnlinkSymbolsALot                         = false                               {product}
     bool Use486InstrsOnly                          = false                               {ARCH product}
     bool UseAES                                    = false                               {product}
     bool UseAESIntrinsics                          = false                               {product}
     intx UseAVX                                    = 99                                  {ARCH product}
     bool UseAdaptiveGCBoundary                     = false                               {product}
     bool UseAdaptiveGenerationSizePolicyAtMajorCollection  = true                                {product}
     bool UseAdaptiveGenerationSizePolicyAtMinorCollection  = true                                {product}
     bool UseAdaptiveNUMAChunkSizing                = true                                {product}
     bool UseAdaptiveSizeDecayMajorGCCost           = true                                {product}
     bool UseAdaptiveSizePolicy                     = true                                {product}
     bool UseAdaptiveSizePolicyFootprintGoal        = true                                {product}
     bool UseAdaptiveSizePolicyWithSystemGC         = false                               {product}
     bool UseAddressNop                             = false                               {ARCH product}
     bool UseAltSigs                                = false                               {product}
     bool UseAutoGCSelectPolicy                     = false                               {product}
     bool UseBMI1Instructions                       = false                               {ARCH product}
     bool UseBMI2Instructions                       = false                               {ARCH product}
     bool UseBiasedLocking                          = true                                {product}
     bool UseBimorphicInlining                      = true                                {C2 product}
     bool UseBoundThreads                           = true                                {product}
     bool UseCLMUL                                  = false                               {ARCH product}
     bool UseCMSBestFit                             = true                                {product}
     bool UseCMSCollectionPassing                   = true                                {product}
     bool UseCMSCompactAtFullCollection             = true                                {product}
     bool UseCMSInitiatingOccupancyOnly             = false                               {product}
     bool UseCRC32Intrinsics                        = false                               {product}
     bool UseCodeCacheFlushing                      = true                                {product}
     bool UseCompiler                               = true                                {product}
     bool UseCompilerSafepoints                     = true                                {product}
     bool UseCompressedClassPointers                = false                               {lp64_product}
     bool UseCompressedOops                         = false                               {lp64_product}
     bool UseConcMarkSweepGC                        = false                               {product}
     bool UseCondCardMark                           = false                               {C2 product}
     bool UseCountLeadingZerosInstruction           = false                               {ARCH product}
     bool UseCountTrailingZerosInstruction          = false                               {ARCH product}
     bool UseCountedLoopSafepoints                  = false                               {C2 product}
     bool UseCounterDecay                           = true                                {product}
     bool UseDivMod                                 = true                                {C2 product}
     bool UseDynamicNumberOfGCThreads               = false                               {product}
     bool UseFPUForSpilling                         = false                               {C2 product}
     bool UseFastAccessorMethods                    = true                                {product}
     bool UseFastEmptyMethods                       = true                                {product}
     bool UseFastJNIAccessors                       = true                                {product}
     bool UseFastStosb                              = false                               {ARCH product}
     bool UseG1GC                                   = false                               {product}
     bool UseGCLogFileRotation                      = false                               {product}
     bool UseGCOverheadLimit                        = true                                {product}
     bool UseGCTaskAffinity                         = false                               {product}
     bool UseGHASHIntrinsics                        = false                               {product}
     bool UseHeavyMonitors                          = false                               {product}
     bool UseInlineCaches                           = true                                {product}
     bool UseInterpreter                            = true                                {product}
     bool UseJumpTables                             = true                                {C2 product}
     bool UseLWPSynchronization                     = true                                {product}
     bool UseLargePages                             = false                               {pd product}
     bool UseLargePagesInMetaspace                  = false                               {product}
     bool UseLargePagesIndividualAllocation        := false                               {pd product}
     bool UseLockedTracing                          = false                               {product}
     bool UseLoopCounter                            = true                                {product}
     bool UseLoopInvariantCodeMotion                = true                                {C1 product}
     bool UseLoopPredicate                          = true                                {C2 product}
     bool UseMathExactIntrinsics                    = true                                {C2 product}
     bool UseMaximumCompactionOnSystemGC            = true                                {product}
     bool UseMembar                                 = false                               {pd product}
     bool UseMontgomeryMultiplyIntrinsic            = false                               {C2 product}
     bool UseMontgomerySquareIntrinsic              = false                               {C2 product}
     bool UseMulAddIntrinsic                        = false                               {C2 product}
     bool UseMultiplyToLenIntrinsic                 = false                               {C2 product}
     bool UseNUMA                                   = false                               {product}
     bool UseNUMAInterleaving                       = false                               {product}
     bool UseNewLongLShift                          = false                               {ARCH product}
     bool UseOSErrorReporting                       = false                               {pd product}
     bool UseOldInlining                            = true                                {C2 product}
     bool UseOnStackReplacement                     = true                                {pd product}
     bool UseOnlyInlinedBimorphic                   = true                                {C2 product}
     bool UseOptoBiasInlining                       = true                                {C2 product}
     bool UsePSAdaptiveSurvivorSizePolicy           = true                                {product}
     bool UseParNewGC                               = false                               {product}
     bool UseParallelGC                             = false                               {product}
     bool UseParallelOldGC                          = false                               {product}
     bool UsePerfData                               = true                                {product}
     bool UsePopCountInstruction                    = false                               {product}
     bool UseRDPCForConstantTableBase               = false                               {C2 product}
     bool UseRTMDeopt                               = false                               {ARCH product}
     bool UseRTMLocking                             = false                               {ARCH product}
     bool UseSHA                                    = false                               {product}
     bool UseSHA1Intrinsics                         = false                               {product}
     bool UseSHA256Intrinsics                       = false                               {product}
     bool UseSHA512Intrinsics                       = false                               {product}
     intx UseSSE                                    = 99                                  {product}
     bool UseSSE42Intrinsics                        = false                               {product}
     bool UseSerialGC                               = false                               {product}
     bool UseSharedSpaces                           = true                                {product}
     bool UseSignalChaining                         = true                                {product}
     bool UseSquareToLenIntrinsic                   = false                               {C2 product}
     bool UseStoreImmI16                            = true                                {ARCH product}
     bool UseStringDeduplication                    = false                               {product}
     bool UseSuperWord                              = true                                {C2 product}
     bool UseTLAB                                   = true                                {pd product}
     bool UseThreadPriorities                       = true                                {pd product}
     bool UseTypeProfile                            = true                                {product}
     bool UseTypeSpeculation                        = true                                {C2 product}
     bool UseUTCFileTimestamp                       = true                                {product}
     bool UseUnalignedLoadStores                    = false                               {ARCH product}
     bool UseVMInterruptibleIO                      = false                               {product}
     bool UseXMMForArrayCopy                        = false                               {product}
     bool UseXmmI2D                                 = false                               {ARCH product}
     bool UseXmmI2F                                 = false                               {ARCH product}
     bool UseXmmLoadAndClearUpper                   = true                                {ARCH product}
     bool UseXmmRegToRegMoveAll                     = false                               {ARCH product}
     bool VMThreadHintNoPreempt                     = false                               {product}
     intx VMThreadPriority                          = -1                                  {product}
     intx VMThreadStackSize                         = 0                                   {pd product}
     intx ValueMapInitialSize                       = 11                                  {C1 product}
     intx ValueMapMaxLoopSize                       = 8                                   {C1 product}
     intx ValueSearchLimit                          = 1000                                {C2 product}
     bool VerifyMergedCPBytecodes                   = true                                {product}
     bool VerifySharedSpaces                        = false                               {product}
     intx WorkAroundNPTLTimedWaitHang               = 1                                   {product}
    uintx YoungGenerationSizeIncrement              = 20                                  {product}
    uintx YoungGenerationSizeSupplement             = 80                                  {product}
    uintx YoungGenerationSizeSupplementDecay        = 8                                   {product}
    uintx YoungPLABSize                             = 4096                                {product}
     bool ZeroTLAB                                  = false                               {product}
     intx hashCode                                  = 5                                   {product}

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731

JVM改过以后的值

命令：java -XX:+PrintFlagsFinal

E:\workspace\study-guigu> java -XX:+PrintFlagsFinal -version
[Global flags]
     intx ActiveProcessorCount                      = -1                                  {product}
    uintx AdaptiveSizeDecrementScaleFactor          = 4                                   {product}
    uintx AdaptiveSizeMajorGCDecayTimeScale         = 10                                  {product}
    uintx AdaptiveSizePausePolicy                   = 0                                   {product}
    uintx AdaptiveSizePolicyCollectionCostMargin    = 50                                  {product}
    uintx AdaptiveSizePolicyInitializingSteps       = 20                                  {product}
    uintx AdaptiveSizePolicyOutputInterval          = 0                                   {product}
    uintx AdaptiveSizePolicyWeight                  = 10                                  {product}
    uintx AdaptiveSizeThroughPutPolicy              = 0                                   {product}
    uintx AdaptiveTimeWeight                        = 25                                  {product}
     bool AdjustConcurrency                         = false                               {product}
     bool AggressiveHeap                            = false                               {product}
     bool AggressiveOpts                            = false                               {product}
     intx AliasLevel                                = 3                                   {C2 product}
     bool AlignVector                               = false                               {C2 product}
     intx AllocateInstancePrefetchLines             = 1                                   {product}
     intx AllocatePrefetchDistance                  = 192                                 {product}
     intx AllocatePrefetchInstr                     = 3                                   {product}
     intx AllocatePrefetchLines                     = 4                                   {product}
     intx AllocatePrefetchStepSize                  = 64                                  {product}
     intx AllocatePrefetchStyle                     = 1                                   {product}
     bool AllowJNIEnvProxy                          = false                               {product}
     bool AllowNonVirtualCalls                      = false                               {product}
     bool AllowParallelDefineClass                  = false                               {product}
     bool AllowUserSignalHandlers                   = false                               {product}
     bool AlwaysActAsServerClassMachine             = false                               {product}
     bool AlwaysCompileLoopMethods                  = false                               {product}
     bool AlwaysLockClassLoader                     = false                               {product}
     bool AlwaysPreTouch                            = false                               {product}
     bool AlwaysRestoreFPU                          = false                               {product}
     bool AlwaysTenure                              = false                               {product}
     bool AssertOnSuspendWaitFailure                = false                               {product}
     bool AssumeMP                                  = false                               {product}
     intx AutoBoxCacheMax                           = 128                                 {C2 product}
    uintx AutoGCSelectPauseMillis                   = 5000                                {product}
     intx BCEATraceLevel                            = 0                                   {product}
     intx BackEdgeThreshold                         = 100000                              {pd product}
     bool BackgroundCompilation                     = true                                {pd product}
    uintx BaseFootPrintEstimate                     = 268435456                           {product}
     intx BiasedLockingBulkRebiasThreshold          = 20                                  {product}
     intx BiasedLockingBulkRevokeThreshold          = 40                                  {product}
     intx BiasedLockingDecayTime                    = 25000                               {product}
     intx BiasedLockingStartupDelay                 = 4000                                {product}
     bool BindGCTaskThreadsToCPUs                   = false                               {product}
     bool BlockLayoutByFrequency                    = true                                {C2 product}
     intx BlockLayoutMinDiamondPercentage           = 20                                  {C2 product}
     bool BlockLayoutRotateLoops                    = true                                {C2 product}
     bool BranchOnRegister                          = false                               {C2 product}
     bool BytecodeVerificationLocal                 = false                               {product}
     bool BytecodeVerificationRemote                = true                                {product}
     bool C1OptimizeVirtualCallProfiling            = true                                {C1 product}
     bool C1ProfileBranches                         = true                                {C1 product}
     bool C1ProfileCalls                            = true                                {C1 product}
     bool C1ProfileCheckcasts                       = true                                {C1 product}
     bool C1ProfileInlinedCalls                     = true                                {C1 product}
     bool C1ProfileVirtualCalls                     = true                                {C1 product}
     bool C1UpdateMethodData                        = true                                {C1 product}
     intx CICompilerCount                          := 3                                   {product}
     bool CICompilerCountPerCPU                     = true                                {product}
     bool CITime                                    = false                               {product}
     bool CMSAbortSemantics                         = false                               {product}
    uintx CMSAbortablePrecleanMinWorkPerIteration   = 100                                 {product}
     intx CMSAbortablePrecleanWaitMillis            = 100                                 {manageable}
    uintx CMSBitMapYieldQuantum                     = 10485760                            {product}
    uintx CMSBootstrapOccupancy                     = 50                                  {product}
     bool CMSClassUnloadingEnabled                  = true                                {product}
    uintx CMSClassUnloadingMaxInterval              = 0                                   {product}
     bool CMSCleanOnEnter                           = true                                {product}
     bool CMSCompactWhenClearAllSoftRefs            = true                                {product}
    uintx CMSConcMarkMultiple                       = 32                                  {product}
     bool CMSConcurrentMTEnabled                    = true                                {product}
    uintx CMSCoordinatorYieldSleepCount             = 10                                  {product}
     bool CMSDumpAtPromotionFailure                 = false                               {product}
     bool CMSEdenChunksRecordAlways                 = true                                {product}
    uintx CMSExpAvgFactor                           = 50                                  {product}
     bool CMSExtrapolateSweep                       = false                               {product}
    uintx CMSFullGCsBeforeCompaction                = 0                                   {product}
    uintx CMSIncrementalDutyCycle                   = 10                                  {product}
    uintx CMSIncrementalDutyCycleMin                = 0                                   {product}
     bool CMSIncrementalMode                        = false                               {product}
    uintx CMSIncrementalOffset                      = 0                                   {product}
     bool CMSIncrementalPacing                      = true                                {product}
    uintx CMSIncrementalSafetyFactor                = 10                                  {product}
    uintx CMSIndexedFreeListReplenish               = 4                                   {product}
     intx CMSInitiatingOccupancyFraction            = -1                                  {product}
    uintx CMSIsTooFullPercentage                    = 98                                  {product}
   double CMSLargeCoalSurplusPercent                = 0.950000                            {product}
   double CMSLargeSplitSurplusPercent               = 1.000000                            {product}
     bool CMSLoopWarn                               = false                               {product}
    uintx CMSMaxAbortablePrecleanLoops              = 0                                   {product}
     intx CMSMaxAbortablePrecleanTime               = 5000                                {product}
    uintx CMSOldPLABMax                             = 1024                                {product}
    uintx CMSOldPLABMin                             = 16                                  {product}
    uintx CMSOldPLABNumRefills                      = 4                                   {product}
    uintx CMSOldPLABReactivityFactor                = 2                                   {product}
     bool CMSOldPLABResizeQuicker                   = false                               {product}
    uintx CMSOldPLABToleranceFactor                 = 4                                   {product}
     bool CMSPLABRecordAlways                       = true                                {product}
    uintx CMSParPromoteBlocksToClaim                = 16                                  {product}
     bool CMSParallelInitialMarkEnabled             = true                                {product}
     bool CMSParallelRemarkEnabled                  = true                                {product}
     bool CMSParallelSurvivorRemarkEnabled          = true                                {product}
    uintx CMSPrecleanDenominator                    = 3                                   {product}
    uintx CMSPrecleanIter                           = 3                                   {product}
    uintx CMSPrecleanNumerator                      = 2                                   {product}
     bool CMSPrecleanRefLists1                      = true                                {product}
     bool CMSPrecleanRefLists2                      = false                               {product}
     bool CMSPrecleanSurvivors1                     = false                               {product}
     bool CMSPrecleanSurvivors2                     = true                                {product}
    uintx CMSPrecleanThreshold                      = 1000                                {product}
     bool CMSPrecleaningEnabled                     = true                                {product}
     bool CMSPrintChunksInDump                      = false                               {product}
     bool CMSPrintEdenSurvivorChunks                = false                               {product}
     bool CMSPrintObjectsInDump                     = false                               {product}
    uintx CMSRemarkVerifyVariant                    = 1                                   {product}
     bool CMSReplenishIntermediate                  = true                                {product}
    uintx CMSRescanMultiple                         = 32                                  {product}
    uintx CMSSamplingGrain                          = 16384                               {product}
     bool CMSScavengeBeforeRemark                   = false                               {product}
    uintx CMSScheduleRemarkEdenPenetration          = 50                                  {product}
    uintx CMSScheduleRemarkEdenSizeThreshold        = 2097152                             {product}
    uintx CMSScheduleRemarkSamplingRatio            = 5                                   {product}
   double CMSSmallCoalSurplusPercent                = 1.050000                            {product}
   double CMSSmallSplitSurplusPercent               = 1.100000                            {product}
     bool CMSSplitIndexedFreeListBlocks             = true                                {product}
     intx CMSTriggerInterval                        = -1                                  {manageable}
    uintx CMSTriggerRatio                           = 80                                  {product}
     intx CMSWaitDuration                           = 2000                                {manageable}
    uintx CMSWorkQueueDrainThreshold                = 10                                  {product}
     bool CMSYield                                  = true                                {product}
    uintx CMSYieldSleepCount                        = 0                                   {product}
    uintx CMSYoungGenPerWorker                      = 67108864                            {pd product}
    uintx CMS_FLSPadding                            = 1                                   {product}
    uintx CMS_FLSWeight                             = 75                                  {product}
    uintx CMS_SweepPadding                          = 1                                   {product}
    uintx CMS_SweepTimerThresholdMillis             = 10                                  {product}
    uintx CMS_SweepWeight                           = 75                                  {product}
     bool CheckEndorsedAndExtDirs                   = false                               {product}
     bool CheckJNICalls                             = false                               {product}
     bool ClassUnloading                            = true                                {product}
     bool ClassUnloadingWithConcurrentMark          = true                                {product}
     intx ClearFPUAtPark                            = 0                                   {product}
     bool ClipInlining                              = true                                {product}
    uintx CodeCacheExpansionSize                    = 65536                               {pd product}
    uintx CodeCacheMinimumFreeSpace                 = 512000                              {product}
     bool CollectGen0First                          = false                               {product}
     bool CompactFields                             = true                                {product}
     intx CompilationPolicyChoice                   = 3                                   {product}
ccstrlist CompileCommand                            =                                     {product}
    ccstr CompileCommandFile                        =                                     {product}
ccstrlist CompileOnly                               =                                     {product}
     intx CompileThreshold                          = 10000                               {pd product}
     bool CompilerThreadHintNoPreempt               = true                                {product}
     intx CompilerThreadPriority                    = -1                                  {product}
     intx CompilerThreadStackSize                   = 0                                   {pd product}
    uintx CompressedClassSpaceSize                  = 1073741824                          {product}
    uintx ConcGCThreads                             = 0                                   {product}
     intx ConditionalMoveLimit                      = 3                                   {C2 pd product}
     intx ContendedPaddingWidth                     = 128                                 {product}
     bool ConvertSleepToYield                       = true                                {pd product}
     bool ConvertYieldToSleep                       = false                               {product}
     bool CrashOnOutOfMemoryError                   = false                               {product}
     bool CreateMinidumpOnCrash                     = false                               {product}
     bool CriticalJNINatives                        = true                                {product}
     bool DTraceAllocProbes                         = false                               {product}
     bool DTraceMethodProbes                        = false                               {product}
     bool DTraceMonitorProbes                       = false                               {product}
     bool Debugging                                 = false                               {product}
    uintx DefaultMaxRAMFraction                     = 4                                   {product}
     intx DefaultThreadPriority                     = -1                                  {product}
     intx DeferPollingPageLoopCount                 = -1                                  {product}
     intx DeferThrSuspendLoopCount                  = 4000                                {product}
     bool DeoptimizeRandom                          = false                               {product}
     bool DisableAttachMechanism                    = false                               {product}
     bool DisableExplicitGC                         = false                               {product}
     bool DisplayVMOutputToStderr                   = false                               {product}
     bool DisplayVMOutputToStdout                   = false                               {product}
     bool DoEscapeAnalysis                          = true                                {C2 product}
     bool DontCompileHugeMethods                    = true                                {product}
     bool DontYieldALot                             = false                               {pd product}
    ccstr DumpLoadedClassList                       =                                     {product}
     bool DumpReplayDataOnError                     = true                                {product}
     bool DumpSharedSpaces                          = false                               {product}
     bool EagerXrunInit                             = false                               {product}
     intx EliminateAllocationArraySizeLimit         = 64                                  {C2 product}
     bool EliminateAllocations                      = true                                {C2 product}
     bool EliminateAutoBox                          = true                                {C2 product}
     bool EliminateLocks                            = true                                {C2 product}
     bool EliminateNestedLocks                      = true                                {C2 product}
     intx EmitSync                                  = 0                                   {product}
     bool EnableContended                           = true                                {product}
     bool EnableResourceManagementTLABCache         = true                                {product}
     bool EnableSharedLookupCache                   = true                                {product}
     bool EnableTracing                             = false                               {product}
    uintx ErgoHeapSizeLimit                         = 0                                   {product}
    ccstr ErrorFile                                 =                                     {product}
    ccstr ErrorReportServer                         =                                     {product}
   double EscapeAnalysisTimeout                     = 20.000000                           {C2 product}
     bool EstimateArgEscape                         = true                                {product}
     bool ExitOnOutOfMemoryError                    = false                               {product}
     bool ExplicitGCInvokesConcurrent               = false                               {product}
     bool ExplicitGCInvokesConcurrentAndUnloadsClasses  = false                               {product}
     bool ExtendedDTraceProbes                      = false                               {product}
    ccstr ExtraSharedClassListFile                  =                                     {product}
     bool FLSAlwaysCoalesceLarge                    = false                               {product}
    uintx FLSCoalescePolicy                         = 2                                   {product}
   double FLSLargestBlockCoalesceProximity          = 0.990000                            {product}
     bool FailOverToOldVerifier                     = true                                {product}
     bool FastTLABRefill                            = true                                {product}
     intx FenceInstruction                          = 0                                   {ARCH product}
     intx FieldsAllocationStyle                     = 1                                   {product}
     bool FilterSpuriousWakeups                     = true                                {product}
    ccstr FlightRecorderOptions                     =                                     {product}
     bool ForceNUMA                                 = false                               {product}
     bool ForceTimeHighResolution                   = false                               {product}
     intx FreqInlineSize                            = 325                                 {pd product}
   double G1ConcMarkStepDurationMillis              = 10.000000                           {product}
    uintx G1ConcRSHotCardLimit                      = 4                                   {product}
    uintx G1ConcRSLogCacheSize                      = 10                                  {product}
     intx G1ConcRefinementGreenZone                 = 0                                   {product}
     intx G1ConcRefinementRedZone                   = 0                                   {product}
     intx G1ConcRefinementServiceIntervalMillis     = 300                                 {product}
    uintx G1ConcRefinementThreads                   = 0                                   {product}
     intx G1ConcRefinementThresholdStep             = 0                                   {product}
     intx G1ConcRefinementYellowZone                = 0                                   {product}
    uintx G1ConfidencePercent                       = 50                                  {product}
    uintx G1HeapRegionSize                          = 0                                   {product}
    uintx G1HeapWastePercent                        = 5                                   {product}
    uintx G1MixedGCCountTarget                      = 8                                   {product}
     intx G1RSetRegionEntries                       = 0                                   {product}
    uintx G1RSetScanBlockSize                       = 64                                  {product}
     intx G1RSetSparseRegionEntries                 = 0                                   {product}
     intx G1RSetUpdatingPauseTimePercent            = 10                                  {product}
     intx G1RefProcDrainInterval                    = 10                                  {product}
    uintx G1ReservePercent                          = 10                                  {product}
    uintx G1SATBBufferEnqueueingThresholdPercent    = 60                                  {product}
     intx G1SATBBufferSize                          = 1024                                {product}
     intx G1UpdateBufferSize                        = 256                                 {product}
     bool G1UseAdaptiveConcRefinement               = true                                {product}
    uintx GCDrainStackTargetSize                    = 64                                  {product}
    uintx GCHeapFreeLimit                           = 2                                   {product}
    uintx GCLockerEdenExpansionPercent              = 5                                   {product}
     bool GCLockerInvokesConcurrent                 = false                               {product}
    uintx GCLogFileSize                             = 8192                                {product}
    uintx GCPauseIntervalMillis                     = 0                                   {product}
    uintx GCTaskTimeStampEntries                    = 200                                 {product}
    uintx GCTimeLimit                               = 98                                  {product}
    uintx GCTimeRatio                               = 99                                  {product}
    uintx HeapBaseMinAddress                        = 2147483648                          {pd product}
     bool HeapDumpAfterFullGC                       = false                               {manageable}
     bool HeapDumpBeforeFullGC                      = false                               {manageable}
     bool HeapDumpOnOutOfMemoryError                = false                               {manageable}
    ccstr HeapDumpPath                              =                                     {manageable}
    uintx HeapFirstMaximumCompactionCount           = 3                                   {product}
    uintx HeapMaximumCompactionInterval             = 20                                  {product}
    uintx HeapSizePerGCThread                       = 87241520                            {product}
     bool IgnoreEmptyClassPaths                     = false                               {product}
     bool IgnoreUnrecognizedVMOptions               = false                               {product}
    uintx IncreaseFirstTierCompileThresholdAt       = 50                                  {product}
     bool IncrementalInline                         = true                                {C2 product}
    uintx InitialBootClassLoaderMetaspaceSize       = 4194304                             {product}
    uintx InitialCodeCacheSize                      = 2555904                             {pd product}
    uintx InitialHeapSize                          := 134217728                           {product}
    uintx InitialRAMFraction                        = 64                                  {product}
   double InitialRAMPercentage                      = 1.562500                            {product}
    uintx InitialSurvivorRatio                      = 8                                   {product}
    uintx InitialTenuringThreshold                  = 7                                   {product}
    uintx InitiatingHeapOccupancyPercent            = 45                                  {product}
     bool Inline                                    = true                                {product}
    ccstr InlineDataFile                            =                                     {product}
     intx InlineSmallCode                           = 2000                                {pd product}
     bool InlineSynchronizedMethods                 = true                                {C1 product}
     bool InsertMemBarAfterArraycopy                = true                                {C2 product}
     intx InteriorEntryAlignment                    = 16                                  {C2 pd product}
     intx InterpreterProfilePercentage              = 33                                  {product}
     bool JNIDetachReleasesMonitors                 = true                                {product}
     bool JavaMonitorsInStackTrace                  = true                                {product}
     intx JavaPriority10_To_OSPriority              = -1                                  {product}
     intx JavaPriority1_To_OSPriority               = -1                                  {product}
     intx JavaPriority2_To_OSPriority               = -1                                  {product}
     intx JavaPriority3_To_OSPriority               = -1                                  {product}
     intx JavaPriority4_To_OSPriority               = -1                                  {product}
     intx JavaPriority5_To_OSPriority               = -1                                  {product}
     intx JavaPriority6_To_OSPriority               = -1                                  {product}
     intx JavaPriority7_To_OSPriority               = -1                                  {product}
     intx JavaPriority8_To_OSPriority               = -1                                  {product}
     intx JavaPriority9_To_OSPriority               = -1                                  {product}
     bool LIRFillDelaySlots                         = false                               {C1 pd product}
    uintx LargePageHeapSizeThreshold                = 134217728                           {product}
    uintx LargePageSizeInBytes                      = 0                                   {product}
     bool LazyBootClassLoader                       = true                                {product}
     intx LiveNodeCountInliningCutoff               = 40000                               {C2 product}
     bool LogCommercialFeatures                     = false                               {product}
     intx LoopMaxUnroll                             = 16                                  {C2 product}
     intx LoopOptsCount                             = 43                                  {C2 product}
     intx LoopUnrollLimit                           = 60                                  {C2 pd product}
     intx LoopUnrollMin                             = 4                                   {C2 product}
     bool LoopUnswitching                           = true                                {C2 product}
     bool ManagementServer                          = false                               {product}
    uintx MarkStackSize                             = 4194304                             {product}
    uintx MarkStackSizeMax                          = 536870912                           {product}
    uintx MarkSweepAlwaysCompactCount               = 4                                   {product}
    uintx MarkSweepDeadRatio                        = 1                                   {product}
     intx MaxBCEAEstimateLevel                      = 5                                   {product}
     intx MaxBCEAEstimateSize                       = 150                                 {product}
    uintx MaxDirectMemorySize                       = 0                                   {product}
     bool MaxFDLimit                                = true                                {product}
    uintx MaxGCMinorPauseMillis                     = 4294967295                          {product}
    uintx MaxGCPauseMillis                          = 4294967295                          {product}
    uintx MaxHeapFreeRatio                          = 100                                 {manageable}
    uintx MaxHeapSize                              := 2126512128                          {product}
     intx MaxInlineLevel                            = 9                                   {product}
     intx MaxInlineSize                             = 35                                  {product}
     intx MaxJNILocalCapacity                       = 65536                               {product}
     intx MaxJavaStackTraceDepth                    = 1024                                {product}
     intx MaxJumpTableSize                          = 65000                               {C2 product}
     intx MaxJumpTableSparseness                    = 5                                   {C2 product}
     intx MaxLabelRootDepth                         = 1100                                {C2 product}
     intx MaxLoopPad                                = 11                                  {C2 product}
    uintx MaxMetaspaceExpansion                     = 5451776                             {product}
    uintx MaxMetaspaceFreeRatio                     = 70                                  {product}
    uintx MaxMetaspaceSize                          = 4294901760                          {product}
    uintx MaxNewSize                               := 708837376                           {product}
     intx MaxNodeLimit                              = 75000                               {C2 product}
 uint64_t MaxRAM                                    = 0                                   {pd product}
    uintx MaxRAMFraction                            = 4                                   {product}
   double MaxRAMPercentage                          = 25.000000                           {product}
     intx MaxRecursiveInlineLevel                   = 1                                   {product}
    uintx MaxTenuringThreshold                      = 15                                  {product}
     intx MaxTrivialSize                            = 6                                   {product}
     intx MaxVectorSize                             = 32                                  {C2 product}
    uintx MetaspaceSize                             = 21807104                            {pd product}
     bool MethodFlushing                            = true                                {product}
    uintx MinHeapDeltaBytes                        := 524288                              {product}
    uintx MinHeapFreeRatio                          = 0                                   {manageable}
     intx MinInliningThreshold                      = 250                                 {product}
     intx MinJumpTableSize                          = 10                                  {C2 pd product}
    uintx MinMetaspaceExpansion                     = 339968                              {product}
    uintx MinMetaspaceFreeRatio                     = 40                                  {product}
    uintx MinRAMFraction                            = 2                                   {product}
   double MinRAMPercentage                          = 50.000000                           {product}
    uintx MinSurvivorRatio                          = 3                                   {product}
    uintx MinTLABSize                               = 2048                                {product}
     intx MonitorBound                              = 0                                   {product}
     bool MonitorInUseLists                         = false                               {product}
     intx MultiArrayExpandLimit                     = 6                                   {C2 product}
     bool MustCallLoadClassInternal                 = false                               {product}
    uintx NUMAChunkResizeWeight                     = 20                                  {product}
    uintx NUMAInterleaveGranularity                 = 2097152                             {product}
    uintx NUMAPageScanRate                          = 256                                 {product}
    uintx NUMASpaceResizeRate                       = 1073741824                          {product}
     bool NUMAStats                                 = false                               {product}
    ccstr NativeMemoryTracking                      = off                                 {product}
     bool NeedsDeoptSuspend                         = false                               {pd product}
     bool NeverActAsServerClassMachine              = false                               {pd product}
     bool NeverTenure                               = false                               {product}
    uintx NewRatio                                  = 2                                   {product}
    uintx NewSize                                  := 44564480                            {product}
    uintx NewSizeThreadIncrease                     = 5320                                {pd product}
     intx NmethodSweepActivity                      = 10                                  {product}
     intx NmethodSweepCheckInterval                 = 5                                   {product}
     intx NmethodSweepFraction                      = 16                                  {product}
     intx NodeLimitFudgeFactor                      = 2000                                {C2 product}
    uintx NumberOfGCLogFiles                        = 0                                   {product}
     intx NumberOfLoopInstrToAlign                  = 4                                   {C2 product}
     intx ObjectAlignmentInBytes                    = 8                                   {lp64_product}
    uintx OldPLABSize                               = 1024                                {product}
    uintx OldPLABWeight                             = 50                                  {product}
    uintx OldSize                                  := 89653248                            {product}
     bool OmitStackTraceInFastThrow                 = true                                {product}
ccstrlist OnError                                   =                                     {product}
ccstrlist OnOutOfMemoryError                        =                                     {product}
     intx OnStackReplacePercentage                  = 140                                 {pd product}
     bool OptimizeFill                              = true                                {C2 product}
     bool OptimizePtrCompare                        = true                                {C2 product}
     bool OptimizeStringConcat                      = true                                {C2 product}
     bool OptoBundling                              = false                               {C2 pd product}
     intx OptoLoopAlignment                         = 16                                  {pd product}
     bool OptoScheduling                            = false                               {C2 pd product}
    uintx PLABWeight                                = 75                                  {product}
     bool PSChunkLargeArrays                        = true                                {product}
     intx ParGCArrayScanChunk                       = 50                                  {product}
    uintx ParGCDesiredObjsFromOverflowList          = 20                                  {product}
     bool ParGCTrimOverflow                         = true                                {product}
     bool ParGCUseLocalOverflow                     = false                               {product}
    uintx ParallelGCBufferWastePct                  = 10                                  {product}
    uintx ParallelGCThreads                         = 4                                   {product}
     bool ParallelGCVerbose                         = false                               {product}
    uintx ParallelOldDeadWoodLimiterMean            = 50                                  {product}
    uintx ParallelOldDeadWoodLimiterStdDev          = 80                                  {product}
     bool ParallelRefProcBalancingEnabled           = true                                {product}
     bool ParallelRefProcEnabled                    = false                               {product}
     bool PartialPeelAtUnsignedTests                = true                                {C2 product}
     bool PartialPeelLoop                           = true                                {C2 product}
     intx PartialPeelNewPhiDelta                    = 0                                   {C2 product}
    uintx PausePadding                              = 1                                   {product}
     intx PerBytecodeRecompilationCutoff            = 200                                 {product}
     intx PerBytecodeTrapLimit                      = 4                                   {product}
     intx PerMethodRecompilationCutoff              = 400                                 {product}
     intx PerMethodTrapLimit                        = 100                                 {product}
     bool PerfAllowAtExitRegistration               = false                               {product}
     bool PerfBypassFileSystemCheck                 = false                               {product}
     intx PerfDataMemorySize                        = 32768                               {product}
     intx PerfDataSamplingInterval                  = 50                                  {product}
    ccstr PerfDataSaveFile                          =                                     {product}
     bool PerfDataSaveToFile                        = false                               {product}
     bool PerfDisableSharedMem                      = false                               {product}
     intx PerfMaxStringConstLength                  = 1024                                {product}
     intx PreInflateSpin                            = 10                                  {pd product}
     bool PreferInterpreterNativeStubs              = false                               {pd product}
     intx PrefetchCopyIntervalInBytes               = 576                                 {product}
     intx PrefetchFieldsAhead                       = 1                                   {product}
     intx PrefetchScanIntervalInBytes               = 576                                 {product}
     bool PreserveAllAnnotations                    = false                               {product}
     bool PreserveFramePointer                      = false                               {pd product}
    uintx PretenureSizeThreshold                    = 0                                   {product}
     bool PrintAdaptiveSizePolicy                   = false                               {product}
     bool PrintCMSInitiationStatistics              = false                               {product}
     intx PrintCMSStatistics                        = 0                                   {product}
     bool PrintClassHistogram                       = false                               {manageable}
     bool PrintClassHistogramAfterFullGC            = false                               {manageable}
     bool PrintClassHistogramBeforeFullGC           = false                               {manageable}
     bool PrintCodeCache                            = false                               {product}
     bool PrintCodeCacheOnCompilation               = false                               {product}
     bool PrintCommandLineFlags                     = false                               {product}
     bool PrintCompilation                          = false                               {product}
     bool PrintConcurrentLocks                      = false                               {manageable}
     intx PrintFLSCensus                            = 0                                   {product}
     intx PrintFLSStatistics                        = 0                                   {product}
     bool PrintFlagsFinal                          := true                                {product}
     bool PrintFlagsInitial                         = false                               {product}
     bool PrintGC                                   = false                               {manageable}
     bool PrintGCApplicationConcurrentTime          = false                               {product}
     bool PrintGCApplicationStoppedTime             = false                               {product}
     bool PrintGCCause                              = true                                {product}
     bool PrintGCDateStamps                         = false                               {manageable}
     bool PrintGCDetails                            = false                               {manageable}
     bool PrintGCID                                 = false                               {manageable}
     bool PrintGCTaskTimeStamps                     = false                               {product}
     bool PrintGCTimeStamps                         = false                               {manageable}
     bool PrintHeapAtGC                             = false                               {product rw}
     bool PrintHeapAtGCExtended                     = false                               {product rw}
     bool PrintHeapAtSIGBREAK                       = true                                {product}
     bool PrintJNIGCStalls                          = false                               {product}
     bool PrintJNIResolving                         = false                               {product}
     bool PrintOldPLAB                              = false                               {product}
     bool PrintOopAddress                           = false                               {product}
     bool PrintPLAB                                 = false                               {product}
     bool PrintParallelOldGCPhaseTimes              = false                               {product}
     bool PrintPromotionFailure                     = false                               {product}
     bool PrintReferenceGC                          = false                               {product}
     bool PrintSafepointStatistics                  = false                               {product}
     intx PrintSafepointStatisticsCount             = 300                                 {product}
     intx PrintSafepointStatisticsTimeout           = -1                                  {product}
     bool PrintSharedArchiveAndExit                 = false                               {product}
     bool PrintSharedDictionary                     = false                               {product}
     bool PrintSharedSpaces                         = false                               {product}
     bool PrintStringDeduplicationStatistics        = false                               {product}
     bool PrintStringTableStatistics                = false                               {product}
     bool PrintTLAB                                 = false                               {product}
     bool PrintTenuringDistribution                 = false                               {product}
     bool PrintTieredEvents                         = false                               {product}
     bool PrintVMOptions                            = false                               {product}
     bool PrintVMQWaitTime                          = false                               {product}
     bool PrintWarnings                             = true                                {product}
    uintx ProcessDistributionStride                 = 4                                   {product}
     bool ProfileInterpreter                        = true                                {pd product}
     bool ProfileIntervals                          = false                               {product}
     intx ProfileIntervalsTicks                     = 100                                 {product}
     intx ProfileMaturityPercentage                 = 20                                  {product}
     bool ProfileVM                                 = false                               {product}
     bool ProfilerPrintByteCodeStatistics           = false                               {product}
     bool ProfilerRecordPC                          = false                               {product}
    uintx PromotedPadding                           = 3                                   {product}
    uintx QueuedAllocationWarningCount              = 0                                   {product}
    uintx RTMRetryCount                             = 5                                   {ARCH product}
     bool RangeCheckElimination                     = true                                {product}
     intx ReadPrefetchInstr                         = 0                                   {ARCH product}
     bool ReassociateInvariants                     = true                                {C2 product}
     bool ReduceBulkZeroing                         = true                                {C2 product}
     bool ReduceFieldZeroing                        = true                                {C2 product}
     bool ReduceInitialCardMarks                    = true                                {C2 product}
     bool ReduceSignalUsage                         = false                               {product}
     intx RefDiscoveryPolicy                        = 0                                   {product}
     bool ReflectionWrapResolutionErrors            = true                                {product}
     bool RegisterFinalizersAtInit                  = true                                {product}
     bool RelaxAccessControlCheck                   = false                               {product}
    ccstr ReplayDataFile                            =                                     {product}
     bool RequireSharedSpaces                       = false                               {product}
    uintx ReservedCodeCacheSize                     = 251658240                           {pd product}
     bool ResizeOldPLAB                             = true                                {product}
     bool ResizePLAB                                = true                                {product}
     bool ResizeTLAB                                = true                                {pd product}
     bool RestoreMXCSROnJNICalls                    = false                               {product}
     bool RestrictContended                         = true                                {product}
     bool RewriteBytecodes                          = true                                {pd product}
     bool RewriteFrequentPairs                      = true                                {pd product}
     intx SafepointPollOffset                       = 256                                 {C1 pd product}
     intx SafepointSpinBeforeYield                  = 2000                                {product}
     bool SafepointTimeout                          = false                               {product}
     intx SafepointTimeoutDelay                     = 10000                               {product}
     bool ScavengeBeforeFullGC                      = true                                {product}
     intx SelfDestructTimer                         = 0                                   {product}
    uintx SharedBaseAddress                         = 0                                   {product}
    ccstr SharedClassListFile                       =                                     {product}
    uintx SharedMiscCodeSize                        = 122880                              {product}
    uintx SharedMiscDataSize                        = 4194304                             {product}
    uintx SharedReadOnlySize                        = 16777216                            {product}
    uintx SharedReadWriteSize                       = 16777216                            {product}
     bool ShowMessageBoxOnError                     = false                               {product}
     intx SoftRefLRUPolicyMSPerMB                   = 1000                                {product}
     bool SpecialEncodeISOArray                     = true                                {C2 product}
     bool SplitIfBlocks                             = true                                {C2 product}
     intx StackRedPages                             = 1                                   {pd product}
     intx StackShadowPages                          = 6                                   {pd product}
     bool StackTraceInThrowable                     = true                                {product}
     intx StackYellowPages                          = 3                                   {pd product}
     bool StartAttachListener                       = false                               {product}
     intx StarvationMonitorInterval                 = 200                                 {product}
     bool StressLdcRewrite                          = false                               {product}
    uintx StringDeduplicationAgeThreshold           = 3                                   {product}
    uintx StringTableSize                           = 60013                               {product}
     bool SuppressFatalErrorMessage                 = false                               {product}
    uintx SurvivorPadding                           = 3                                   {product}
    uintx SurvivorRatio                             = 8                                   {product}
     intx SuspendRetryCount                         = 50                                  {product}
     intx SuspendRetryDelay                         = 5                                   {product}
     intx SyncFlags                                 = 0                                   {product}
    ccstr SyncKnobs                                 =                                     {product}
     intx SyncVerbose                               = 0                                   {product}
    uintx TLABAllocationWeight                      = 35                                  {product}
    uintx TLABRefillWasteFraction                   = 64                                  {product}
    uintx TLABSize                                  = 0                                   {product}
     bool TLABStats                                 = true                                {product}
    uintx TLABWasteIncrement                        = 4                                   {product}
    uintx TLABWasteTargetPercent                    = 1                                   {product}
    uintx TargetPLABWastePct                        = 10                                  {product}
    uintx TargetSurvivorRatio                       = 50                                  {product}
    uintx TenuredGenerationSizeIncrement            = 20                                  {product}
    uintx TenuredGenerationSizeSupplement           = 80                                  {product}
    uintx TenuredGenerationSizeSupplementDecay      = 2                                   {product}
     intx ThreadPriorityPolicy                      = 0                                   {product}
     bool ThreadPriorityVerbose                     = false                               {product}
    uintx ThreadSafetyMargin                        = 52428800                            {product}
     intx ThreadStackSize                           = 0                                   {pd product}
    uintx ThresholdTolerance                        = 10                                  {product}
     intx Tier0BackedgeNotifyFreqLog                = 10                                  {product}
     intx Tier0InvokeNotifyFreqLog                  = 7                                   {product}
     intx Tier0ProfilingStartPercentage             = 200                                 {product}
     intx Tier23InlineeNotifyFreqLog                = 20                                  {product}
     intx Tier2BackEdgeThreshold                    = 0                                   {product}
     intx Tier2BackedgeNotifyFreqLog                = 14                                  {product}
     intx Tier2CompileThreshold                     = 0                                   {product}
     intx Tier2InvokeNotifyFreqLog                  = 11                                  {product}
     intx Tier3BackEdgeThreshold                    = 60000                               {product}
     intx Tier3BackedgeNotifyFreqLog                = 13                                  {product}
     intx Tier3CompileThreshold                     = 2000                                {product}
     intx Tier3DelayOff                             = 2                                   {product}
     intx Tier3DelayOn                              = 5                                   {product}
     intx Tier3InvocationThreshold                  = 200                                 {product}
     intx Tier3InvokeNotifyFreqLog                  = 10                                  {product}
     intx Tier3LoadFeedback                         = 5                                   {product}
     intx Tier3MinInvocationThreshold               = 100                                 {product}
     intx Tier4BackEdgeThreshold                    = 40000                               {product}
     intx Tier4CompileThreshold                     = 15000                               {product}
     intx Tier4InvocationThreshold                  = 5000                                {product}
     intx Tier4LoadFeedback                         = 3                                   {product}
     intx Tier4MinInvocationThreshold               = 600                                 {product}
     bool TieredCompilation                         = true                                {pd product}
     intx TieredCompileTaskTimeout                  = 50                                  {product}
     intx TieredRateUpdateMaxTime                   = 25                                  {product}
     intx TieredRateUpdateMinTime                   = 1                                   {product}
     intx TieredStopAtLevel                         = 4                                   {product}
     bool TimeLinearScan                            = false                               {C1 product}
     bool TraceBiasedLocking                        = false                               {product}
     bool TraceClassLoading                         = false                               {product rw}
     bool TraceClassLoadingPreorder                 = false                               {product}
     bool TraceClassPaths                           = false                               {product}
     bool TraceClassResolution                      = false                               {product}
     bool TraceClassUnloading                       = false                               {product rw}
     bool TraceDynamicGCThreads                     = false                               {product}
     bool TraceGen0Time                             = false                               {product}
     bool TraceGen1Time                             = false                               {product}
    ccstr TraceJVMTI                                =                                     {product}
     bool TraceLoaderConstraints                    = false                               {product rw}
     bool TraceMetadataHumongousAllocation          = false                               {product}
     bool TraceMonitorInflation                     = false                               {product}
     bool TraceParallelOldGCTasks                   = false                               {product}
     intx TraceRedefineClasses                      = 0                                   {product}
     bool TraceSafepointCleanupTime                 = false                               {product}
     bool TraceSharedLookupCache                    = false                               {product}
     bool TraceSuspendWaitFailures                  = false                               {product}
     intx TrackedInitializationLimit                = 50                                  {C2 product}
     bool TransmitErrorReport                       = false                               {product}
     bool TrapBasedNullChecks                       = false                               {pd product}
     bool TrapBasedRangeChecks                      = false                               {C2 pd product}
     intx TypeProfileArgsLimit                      = 2                                   {product}
    uintx TypeProfileLevel                          = 111                                 {pd product}
     intx TypeProfileMajorReceiverPercent           = 90                                  {C2 product}
     intx TypeProfileParmsLimit                     = 2                                   {product}
     intx TypeProfileWidth                          = 2                                   {product}
     intx UnguardOnExecutionViolation               = 0                                   {product}
     bool UnlinkSymbolsALot                         = false                               {product}
     bool Use486InstrsOnly                          = false                               {ARCH product}
     bool UseAES                                    = true                                {product}
     bool UseAESIntrinsics                          = true                                {product}
     intx UseAVX                                    = 2                                   {ARCH product}
     bool UseAdaptiveGCBoundary                     = false                               {product}
     bool UseAdaptiveGenerationSizePolicyAtMajorCollection  = true                                {product}
     bool UseAdaptiveGenerationSizePolicyAtMinorCollection  = true                                {product}
     bool UseAdaptiveNUMAChunkSizing                = true                                {product}
     bool UseAdaptiveSizeDecayMajorGCCost           = true                                {product}
     bool UseAdaptiveSizePolicy                     = true                                {product}
     bool UseAdaptiveSizePolicyFootprintGoal        = true                                {product}
     bool UseAdaptiveSizePolicyWithSystemGC         = false                               {product}
     bool UseAddressNop                             = true                                {ARCH product}
     bool UseAltSigs                                = false                               {product}
     bool UseAutoGCSelectPolicy                     = false                               {product}
     bool UseBMI1Instructions                       = true                                {ARCH product}
     bool UseBMI2Instructions                       = true                                {ARCH product}
     bool UseBiasedLocking                          = true                                {product}
     bool UseBimorphicInlining                      = true                                {C2 product}
     bool UseBoundThreads                           = true                                {product}
     bool UseCLMUL                                  = true                                {ARCH product}
     bool UseCMSBestFit                             = true                                {product}
     bool UseCMSCollectionPassing                   = true                                {product}
     bool UseCMSCompactAtFullCollection             = true                                {product}
     bool UseCMSInitiatingOccupancyOnly             = false                               {product}
     bool UseCRC32Intrinsics                        = true                                {product}
     bool UseCodeCacheFlushing                      = true                                {product}
     bool UseCompiler                               = true                                {product}
     bool UseCompilerSafepoints                     = true                                {product}
     bool UseCompressedClassPointers               := true                                {lp64_product}
     bool UseCompressedOops                        := true                                {lp64_product}
     bool UseConcMarkSweepGC                        = false                               {product}
     bool UseCondCardMark                           = false                               {C2 product}
     bool UseCountLeadingZerosInstruction           = true                                {ARCH product}
     bool UseCountTrailingZerosInstruction          = true                                {ARCH product}
     bool UseCountedLoopSafepoints                  = false                               {C2 product}
     bool UseCounterDecay                           = true                                {product}
     bool UseDivMod                                 = true                                {C2 product}
     bool UseDynamicNumberOfGCThreads               = false                               {product}
     bool UseFPUForSpilling                         = true                                {C2 product}
     bool UseFastAccessorMethods                    = false                               {product}
     bool UseFastEmptyMethods                       = false                               {product}
     bool UseFastJNIAccessors                       = true                                {product}
     bool UseFastStosb                              = true                                {ARCH product}
     bool UseG1GC                                   = false                               {product}
     bool UseGCLogFileRotation                      = false                               {product}
     bool UseGCOverheadLimit                        = true                                {product}
     bool UseGCTaskAffinity                         = false                               {product}
     bool UseGHASHIntrinsics                        = true                                {product}
     bool UseHeavyMonitors                          = false                               {product}
     bool UseInlineCaches                           = true                                {product}
     bool UseInterpreter                            = true                                {product}
     bool UseJumpTables                             = true                                {C2 product}
     bool UseLWPSynchronization                     = true                                {product}
     bool UseLargePages                             = false                               {pd product}
     bool UseLargePagesInMetaspace                  = false                               {product}
     bool UseLargePagesIndividualAllocation        := false                               {pd product}
     bool UseLockedTracing                          = false                               {product}
     bool UseLoopCounter                            = true                                {product}
     bool UseLoopInvariantCodeMotion                = true                                {C1 product}
     bool UseLoopPredicate                          = true                                {C2 product}
     bool UseMathExactIntrinsics                    = true                                {C2 product}
     bool UseMaximumCompactionOnSystemGC            = true                                {product}
     bool UseMembar                                 = false                               {pd product}
     bool UseMontgomeryMultiplyIntrinsic            = true                                {C2 product}
     bool UseMontgomerySquareIntrinsic              = true                                {C2 product}
     bool UseMulAddIntrinsic                        = true                                {C2 product}
     bool UseMultiplyToLenIntrinsic                 = true                                {C2 product}
     bool UseNUMA                                   = false                               {product}
     bool UseNUMAInterleaving                       = false                               {product}
     bool UseNewLongLShift                          = false                               {ARCH product}
     bool UseOSErrorReporting                       = false                               {pd product}
     bool UseOldInlining                            = true                                {C2 product}
     bool UseOnStackReplacement                     = true                                {pd product}
     bool UseOnlyInlinedBimorphic                   = true                                {C2 product}
     bool UseOptoBiasInlining                       = true                                {C2 product}
     bool UsePSAdaptiveSurvivorSizePolicy           = true                                {product}
     bool UseParNewGC                               = false                               {product}
     bool UseParallelGC                            := true                                {product}
     bool UseParallelOldGC                          = true                                {product}
     bool UsePerfData                               = true                                {product}
     bool UsePopCountInstruction                    = true                                {product}
     bool UseRDPCForConstantTableBase               = false                               {C2 product}
     bool UseRTMDeopt                               = false                               {ARCH product}
     bool UseRTMLocking                             = false                               {ARCH product}
     bool UseSHA                                    = false                               {product}
     bool UseSHA1Intrinsics                         = false                               {product}
     bool UseSHA256Intrinsics                       = false                               {product}
     bool UseSHA512Intrinsics                       = false                               {product}
     intx UseSSE                                    = 4                                   {product}
     bool UseSSE42Intrinsics                        = true                                {product}
     bool UseSerialGC                               = false                               {product}
     bool UseSharedSpaces                           = false                               {product}
     bool UseSignalChaining                         = true                                {product}
     bool UseSquareToLenIntrinsic                   = true                                {C2 product}
     bool UseStoreImmI16                            = false                               {ARCH product}
     bool UseStringDeduplication                    = false                               {product}
     bool UseSuperWord                              = true                                {C2 product}
     bool UseTLAB                                   = true                                {pd product}
     bool UseThreadPriorities                       = true                                {pd product}
     bool UseTypeProfile                            = true                                {product}
     bool UseTypeSpeculation                        = true                                {C2 product}
     bool UseUTCFileTimestamp                       = true                                {product}
     bool UseUnalignedLoadStores                    = true                                {ARCH product}
     bool UseVMInterruptibleIO                      = false                               {product}
     bool UseXMMForArrayCopy                        = true                                {product}
     bool UseXmmI2D                                 = false                               {ARCH product}
     bool UseXmmI2F                                 = false                               {ARCH product}
     bool UseXmmLoadAndClearUpper                   = true                                {ARCH product}
     bool UseXmmRegToRegMoveAll                     = true                                {ARCH product}
     bool VMThreadHintNoPreempt                     = false                               {product}
     intx VMThreadPriority                          = -1                                  {product}
     intx VMThreadStackSize                         = 0                                   {pd product}
     intx ValueMapInitialSize                       = 11                                  {C1 product}
     intx ValueMapMaxLoopSize                       = 8                                   {C1 product}
     intx ValueSearchLimit                          = 1000                                {C2 product}
     bool VerifyMergedCPBytecodes                   = true                                {product}
     bool VerifySharedSpaces                        = false                               {product}
     intx WorkAroundNPTLTimedWaitHang               = 1                                   {product}
    uintx YoungGenerationSizeIncrement              = 20                                  {product}
    uintx YoungGenerationSizeSupplement             = 80                                  {product}
    uintx YoungGenerationSizeSupplementDecay        = 8                                   {product}
    uintx YoungPLABSize                             = 4096                                {product}
     bool ZeroTLAB                                  = false                               {product}
     intx hashCode                                  = 5                                   {product}
java version "1.8.0_231"
Java(TM) SE Runtime Environment (build 1.8.0_231-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.231-b11, mixed mode)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733

-XX:+PrintCommandLineFlags -version 可以查看垃圾回收器

E:\workspace\study-guigu>java -XX:+PrintCommandLineFlags -version
-XX:InitialHeapSize=132899584 -XX:MaxHeapSize=2126393344 -XX:+PrintCommandLineFlags -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:-UseLargePagesIndividualAl
location -XX:+UseParallelGC
java version "1.8.0_231"
Java(TM) SE Runtime Environment (build 1.8.0_231-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.231-b11, mixed mode)

1
2
3
4
5
6
7

JVM常用参数

-Xms：初始化大小内存，默认为物理内存1/64。（等价于-XX:InitialHeapSize）

-Xmx：最大分配内存，默认为物理内存1/4。（等价于-XX:MaxHeapSize）

-Xss：设置单个线程栈的大小，一般默认为512k~1024k。（等价于-XX:ThreadStackSize）

-Xmn：设置年轻代大小

-XX:MetaspaceSize：元空间的本质和永久代类似，都是对JVM规范中方法区的实现。不过元空间于永久代之间最大的区别在于：**元空间并不在虚拟机中，而是使用本地内存。**因此默认情况下，元空间的大小仅受本地内存限制。

-Xms128m -Xmx4096m -Xss1024k -XX:MetaspaceSize=512m -XX:+PrintCommandLineFlags -XX:+PrintGCDetails -XX:+UseSerialGC