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juc之常用4大并发工具类 (四)
- CountDownLatch: 减少计数
- CyclicBarrier: 循环栅栏
- Semaphore: 信号量
- ExChanger: 交换器
1.CountDownLatch
CountDownLatch,俗称闭锁,作用是类似加强版的 Join,是让一组线程等待其他的线程完成工作以后才执行
就比如在启动框架服务的时候,我们主线程需要在环境线程初始化完成之后才能启动,这时候我们就可以实现使用 CountDownLatch 来完成
public CountDownLatch(int count) { if (count < 0) throw new IllegalArgumentException("count < 0"); this.sync = new Sync(count); }- 1
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传入一个 int 类型的参数,将决定在执行次扣减之后,等待的线程被唤醒
主线程中创建 CountDownLatch(3),然后主线程 await 阻塞,然后线程 A,B,C 各自完成了任务,调用了 countDown,之后,每个线程调用一次计数器就会减一,初始是 3,然后 A 线程调用后变成 2,B 线程调用后变成 1,C 线程调用后,变成 0,这时就会唤醒正在 await 的主线程,然后主线程继续执行
线程休眠辅助工具类package org.dance.tools; import java.util.concurrent.TimeUnit; /** * 类说明：线程休眠辅助工具类 */ public class SleepTools { /** * 按秒休眠 * * @param seconds 秒数 */ public static final void second(int seconds) { try { TimeUnit.SECONDS.sleep(seconds); } catch (InterruptedException e) { } } /** * 按毫秒数休眠 * * @param seconds 毫秒数 */ public static final void ms(int seconds) { try { TimeUnit.MILLISECONDS.sleep(seconds); } catch (InterruptedException e) { } } }- 1
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package org.dance.day2.util; import org.dance.tools.SleepTools; import java.util.concurrent.CountDownLatch; /** * CountDownLatch的使用,有五个线程,6个扣除点 * 扣除完成后主线程和业务线程,才能执行工作 * 扣除点一般都是大于等于需要初始化的线程的 */ public class UseCountDownLatch { /** * 设置为6个扣除点 */ static CountDownLatch countDownLatch = new CountDownLatch(6); /** * 初始化线程 */ private static class InitThread implements Runnable { @Override public void run() { System.out.println("thread_" + Thread.currentThread().getId() + " ready init work ....."); // 执行扣减 扣减不代表结束 countDownLatch.countDown(); for (int i = 0; i < 2; i++) { System.out.println("thread_" + Thread.currentThread().getId() + ".....continue do its work"); } } } /** * 业务线程 */ private static class BusiThread implements Runnable { @Override public void run() { // 业务线程需要在等初始化完毕后才能执行 try { countDownLatch.await(); for (int i = 0; i < 3; i++) { System.out.println("BusiThread " + Thread.currentThread().getId() + " do business-----"); } } catch (InterruptedException e) { e.printStackTrace(); } } } public static void main(String[] args) { // 创建单独的初始化线程 new Thread(){ @Override public void run() { SleepTools.ms(1); System.out.println("thread_" + Thread.currentThread().getId() + " ready init work step 1st....."); // 扣减一次 countDownLatch.countDown(); System.out.println("begin stop 2nd....."); SleepTools.ms(1); System.out.println("thread_" + Thread.currentThread().getId() + " ready init work step 2nd....."); // 扣减一次 countDownLatch.countDown(); } }.start(); // 启动业务线程 new Thread(new BusiThread()).start(); // 启动初始化线程 for (int i = 0; i <= 3; i++) { new Thread(new InitThread()).start(); } // 主线程进入等待 try { countDownLatch.await(); System.out.println("Main do ites work....."); } catch (InterruptedException e) { e.printStackTrace(); } } }- 1
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thread_13 ready init work ..... thread_13.....continue do its work thread_13.....continue do its work thread_14 ready init work ..... thread_14.....continue do its work thread_14.....continue do its work thread_15 ready init work ..... thread_15.....continue do its work thread_11 ready init work step 1st..... begin stop 2nd..... thread_16 ready init work ..... thread_16.....continue do its work thread_16.....continue do its work thread_15.....continue do its work thread_11 ready init work step 2nd..... Main do ites work..... BusiThread 12 do business----- BusiThread 12 do business----- BusiThread 12 do business------ 1
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2.CyclicBarrier
CyclicBarrier,俗称栅栏锁,作用是让一组线程到达某个屏障,被阻塞,一直到组内的最后一个线程到达,然后屏障开放,接着,所有的线程继续运行
public CyclicBarrier(int parties) { this(parties, null); }- 1
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public class Demo { public CyclicBarrier(int parties, Runnable barrierAction) { if (parties <= 0) throw new IllegalArgumentException(); this.parties = parties; this.count = parties; this.barrierCommand = barrierAction; } }- 1
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第一个参数也是 Int 类型的,传入的是执行线程的个数,这个数量和 CountDownLatch 不一样,这个数量是需要和线程数量吻合的,CountDownLatch 则不一样,CountDownLatch 可以大于等于,而 CyclicBarrier 只能等于,然后是第二个参数,第二个参数是 barrierAction,这个参数是当屏障开放后,执行的任务线程,如果当屏障开放后需要执行什么任务,可以写在这个线程中
主线程创建 CyclicBarrier(3,barrierAction),然后由线程开始执行,线程 A,B 执行完成后都调用了 await,然后他们都在一个屏障前阻塞者,需要等待线程 C 也,执行完成,调用 await 之后,然后三个线程都达到屏障后,屏障开放,然后线程继续执行,并且 barrierAction 在屏障开放的一瞬间也开始执行
public class UseCyclicBarrier { /** * 存放子线程工作结果的安全容器 */ private static ConcurrentHashMap<String, Long> resultMap = new ConcurrentHashMap<>(); private static CyclicBarrier cyclicBarrier = new CyclicBarrier(5,new CollectThread()); /** * 结果打印线程 * 用来演示CyclicBarrier的第二个参数,barrierAction */ private static class CollectThread implements Runnable { @Override public void run() { StringBuffer result = new StringBuffer(); for (Map.Entry<String, Long> workResult : resultMap.entrySet()) { result.append("[" + workResult.getValue() + "]"); } System.out.println("the result = " + result); System.out.println("do other business....."); } } /** * 工作子线程 * 用于CyclicBarrier的一组线程 */ private static class SubThread implements Runnable { @Override public void run() { // 获取当前线程的ID long id = Thread.currentThread().getId(); // 放入统计容器中 resultMap.put(String.valueOf(id), id); Random random = new Random(); try { if (random.nextBoolean()) { Thread.sleep(1000 + id); System.out.println("Thread_"+id+"..... do something"); } System.out.println(id+" is await"); cyclicBarrier.await(); Thread.sleep(1000+id); System.out.println("Thread_"+id+".....do its business"); } catch (InterruptedException e) { e.printStackTrace(); } catch (BrokenBarrierException e) { e.printStackTrace(); } } } public static void main(String[] args) { for (int i = 0; i <= 4; i++) { Thread thread = new Thread(new SubThread()); thread.start(); } } }- 1
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11 is await 14 is await 15 is await Thread_12..... do something 12 is await Thread_13..... do something 13 is await the result = [11][12][13][14][15] do other business..... Thread_11.....do its business Thread_12.....do its business Thread_13.....do its business Thread_14.....do its business Thread_15.....do its business- 1
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3.Semaphore
Semaphore,俗称信号量,作用于控制同时访问某个特定资源的线程数量,用在流量控制
一说特定资源控制,那么第一时间就想到了数据库连接…
之前用等待超时模式写了一个数据库连接池,打算用这个 Semaphone 也写一个
public Semaphore(int permits) { sync = new NonfairSync(permits); }- 1
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需要传入许可证的数量,这个数量就是资源的最大允许的访问的线程数
基于Semaphore 的数据库连接池
public class SqlConnection implements Connection { /** * 获取数据库连接 * @return */ public static final Connection fetchConnection(){ return new SqlConnection(); } @Override public void commit() throws SQLException { SleepTools.ms(70); } @Override public Statement createStatement() throws SQLException { SleepTools.ms(1); return null; } @Override public PreparedStatement prepareStatement(String sql) throws SQLException { return null; } @Override public CallableStatement prepareCall(String sql) throws SQLException { return null; } @Override public String nativeSQL(String sql) throws SQLException { return null; } @Override public void setAutoCommit(boolean autoCommit) throws SQLException { } @Override public boolean getAutoCommit() throws SQLException { return false; } @Override public void rollback() throws SQLException { } @Override public void close() throws SQLException { } @Override public boolean isClosed() throws SQLException { return false; } @Override public DatabaseMetaData getMetaData() throws SQLException { return null; } @Override public void setReadOnly(boolean readOnly) throws SQLException { } @Override public boolean isReadOnly() throws SQLException { return false; } @Override public void setCatalog(String catalog) throws SQLException { } @Override public String getCatalog() throws SQLException { return null; } @Override public void setTransactionIsolation(int level) throws SQLException { } @Override public int getTransactionIsolation() throws SQLException { return 0; } @Override public SQLWarning getWarnings() throws SQLException { return null; } @Override public void clearWarnings() throws SQLException { } @Override public Statement createStatement(int resultSetType, int resultSetConcurrency) throws SQLException { return null; } @Override public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency) throws SQLException { return null; } @Override public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency) throws SQLException { return null; } @Override public Map<String, Class<?>> getTypeMap() throws SQLException { return null; } @Override public void setTypeMap(Map<String, Class<?>> map) throws SQLException { } @Override public void setHoldability(int holdability) throws SQLException { } @Override public int getHoldability() throws SQLException { return 0; } @Override public Savepoint setSavepoint() throws SQLException { return null; } @Override public Savepoint setSavepoint(String name) throws SQLException { return null; } @Override public void rollback(Savepoint savepoint) throws SQLException { } @Override public void releaseSavepoint(Savepoint savepoint) throws SQLException { } @Override public Statement createStatement(int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException { return null; } @Override public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException { return null; } @Override public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException { return null; } @Override public PreparedStatement prepareStatement(String sql, int autoGeneratedKeys) throws SQLException { return null; } @Override public PreparedStatement prepareStatement(String sql, int[] columnIndexes) throws SQLException { return null; } @Override public PreparedStatement prepareStatement(String sql, String[] columnNames) throws SQLException { return null; } @Override public Clob createClob() throws SQLException { return null; } @Override public Blob createBlob() throws SQLException { return null; } @Override public NClob createNClob() throws SQLException { return null; } @Override public SQLXML createSQLXML() throws SQLException { return null; } @Override public boolean isValid(int timeout) throws SQLException { return false; } @Override public void setClientInfo(String name, String value) throws SQLClientInfoException { } @Override public void setClientInfo(Properties properties) throws SQLClientInfoException { } @Override public String getClientInfo(String name) throws SQLException { return null; } @Override public Properties getClientInfo() throws SQLException { return null; } @Override public Array createArrayOf(String typeName, Object[] elements) throws SQLException { return null; } @Override public Struct createStruct(String typeName, Object[] attributes) throws SQLException { return null; } @Override public void setSchema(String schema) throws SQLException { } @Override public String getSchema() throws SQLException { return null; } @Override public void abort(Executor executor) throws SQLException { } @Override public void setNetworkTimeout(Executor executor, int milliseconds) throws SQLException { } @Override public int getNetworkTimeout() throws SQLException { return 0; } @Override public <T> T unwrap(Class<T> iface) throws SQLException { return null; } @Override public boolean isWrapperFor(Class<?> iface) throws SQLException { return false; } }- 1
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连接池对象
public class DBPoolSemaphore { /** * 池容量 */ private final static int POOL_SIZE = 10; /** * useful 代表可用连接 * useless 代表已用连接 * 为什么要使用两个Semaphore呢?是因为,在连接池中不只有连接本身是资源,空位也是资源,也需要记录 */ private final Semaphore useful, useless; /** * 连接池 */ private final static LinkedList<Connection> POOL = new LinkedList<>(); /** * 使用静态块初始化池 */ static { for (int i = 0; i < POOL_SIZE; i++) { POOL.addLast(SqlConnection.fetchConnection()); } } public DBPoolSemaphore() { // 初始可用的许可证等于池容量 useful = new Semaphore(POOL_SIZE); // 初始不可用的许可证容量为0 useless = new Semaphore(0); } /** * 获取数据库连接 * * @return 连接对象 */ public Connection takeConnection() throws InterruptedException { // 可用许可证减一 useful.acquire(); Connection connection; synchronized (POOL) { connection = POOL.removeFirst(); } // 不可用许可证数量加一 useless.release(); return connection; } /** * 释放链接 * * @param connection 连接对象 */ public void returnConnection(Connection connection) throws InterruptedException { if(null!=connection){ // 打印日志 System.out.println("当前有"+useful.getQueueLength()+"个线程等待获取连接,," +"可用连接有"+useful.availablePermits()+"个"); // 不可用许可证减一 useless.acquire(); synchronized (POOL){ POOL.addLast(connection); } // 可用许可证加一 useful.release(); } } }- 1
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测试
public class UseSemaphore { /** * 连接池 */ public static final DBPoolSemaphore pool = new DBPoolSemaphore(); private static class BusiThread extends Thread{ @Override public void run() { // 随机数工具类 为了让每个线程持有连接的时间不一样 Random random = new Random(); long start = System.currentTimeMillis(); try { Connection connection = pool.takeConnection(); System.out.println("Thread_"+Thread.currentThread().getId()+ "_获取数据库连接耗时["+(System.currentTimeMillis()-start)+"]ms."); // 模拟使用连接查询数据 SleepTools.ms(100+random.nextInt(100)); System.out.println("查询数据完成归还连接"); pool.returnConnection(connection); } catch (InterruptedException e) { e.printStackTrace(); } } } public static void main(String[] args) { for (int i = 0; i < 50; i++) { BusiThread busiThread = new BusiThread(); busiThread.start(); } } }- 1
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Thread_11_获取数据库连接耗时[0]ms. Thread_12_获取数据库连接耗时[0]ms. Thread_13_获取数据库连接耗时[0]ms. Thread_14_获取数据库连接耗时[0]ms. Thread_15_获取数据库连接耗时[0]ms. Thread_16_获取数据库连接耗时[0]ms. Thread_17_获取数据库连接耗时[0]ms. Thread_18_获取数据库连接耗时[0]ms. Thread_19_获取数据库连接耗时[0]ms. Thread_20_获取数据库连接耗时[0]ms. 查询数据完成归还连接 当前有40个线程等待获取连接,,可用连接有0个 Thread_21_获取数据库连接耗时[112]ms. 查询数据完成归还连接 ...................查询数据完成归还连接 当前有2个线程等待获取连接,,可用连接有0个 Thread_59_获取数据库连接耗时[637]ms. 查询数据完成归还连接 当前有1个线程等待获取连接,,可用连接有0个 Thread_60_获取数据库连接耗时[660]ms. 查询数据完成归还连接 当前有0个线程等待获取连接,,可用连接有0个 查询数据完成归还连接................... 当前有0个线程等待获取连接,,可用连接有8个 查询数据完成归还连接 当前有0个线程等待获取连接,,可用连接有9个- 1
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对连接池中的资源的到了控制,这就是信号量的流量控制。
4.Exchanger
Exchanger,俗称交换器,用于在线程之间交换数据,但是比较受限,因为只能两个线程之间交换数据
public Exchanger() { participant = new Participant(); }- 1
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public class UseExchange { private static final Exchanger<Set<String>> exchanger = new Exchanger<>(); public static void main(String[] args) { new Thread(){ @Override public void run() { Set<String> aSet = new HashSet<>(); aSet.add("A"); aSet.add("B"); aSet.add("C"); try { Set<String> exchange = exchanger.exchange(aSet); for (String s : exchange) { System.out.println("aSet"+s); } } catch (InterruptedException e) { e.printStackTrace(); } } }.start(); new Thread(){ @Override public void run() { Set<String> bSet = new HashSet<>(); bSet.add("1"); bSet.add("2"); bSet.add("3"); try { Set<String> exchange = exchanger.exchange(bSet); for (String s : exchange) { System.out.println("bSet"+s); } } catch (InterruptedException e) { e.printStackTrace(); } } }.start(); } }- 1
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- 36
- 37
- 38
- 39
- 40
- 41
- 42
- 43
- 44
- 45
执行结果:
bSetA bSetB bSetC aSet1 aSet2 aSet3- 1
- 2
- 3
- 4
- 5
- 6
两个线程中的数据发生了交换,这就是 Exchanger 的线程数据交换了。
-
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- 原文地址：https://blog.csdn.net/qq_43141726/article/details/127905320
