多线程 CompletableFuture(2)

一、CompletableFuture 常用方法
3、对计算结果进行消费
1、对比补充

• thenRun(Runable runable)
  • 任务A执行完任务B,并且B不需要A的结果
• thenAccept(Consumer action)
  • 任务A执行完执行任务B，B需要A的结果，但是任务B无返回值
• thenApply(Function fn)
  • 任务A执行完执行任务B，B需要A的结果，同时任务B有返回值
    2、CompletableFuture和线程池说明

1. 没有传入自定义线程池，都是用默认线程池ForkJoinPool
2. 传入 一个自定义线程池
   • 如果你执行第一个任务的时候 ，传入了一个自定义线程池
   • 调用thenRun方法执行第二个任务时，则第二个任务和第一个任务共用一个线程池
   • 调用thenRunAsync执行第二个任务时，则第一个任务使用的是你自己传入的线程池，第二个任务使用的是ForkJoinPool线程池
3. 备注
   • 有可能处理太快，系统优化切换原则，直接使用main线程处理
     //线程池说明
     public class CompletableFutureWithThreadPool {
     public static void main(String[] args) {
     ExecutorService threadPool = Executors.newFixedThreadPool(5);
     try {
     CompletableFuture future = CompletableFuture.supplyAsync(() -> {
     // try {
     // Thread.sleep(20);
     // } catch (InterruptedException e) {
     // e.printStackTrace();
     // }
     System.out.println(“一号任务” + Thread.currentThread().getName());
     return “abcd”;
     },threadPool).thenRun(() -> {
     try {
     Thread.sleep(10);
     } catch (InterruptedException e) {
     e.printStackTrace();
     }
     System.out.println(“二号任务” + Thread.currentThread().getName());
     }).thenRun(() -> {
     try {
     Thread.sleep(10);
     } catch (InterruptedException e) {
     e.printStackTrace();
     }
     System.out.println(“三号任务” + Thread.currentThread().getName());
     }).thenRun(() -> {
     try {
     Thread.sleep(10);
     } catch (InterruptedException e) {
     e.printStackTrace();
     }
     System.out.println(“四号任务” + Thread.currentThread().getName());
     }).thenRun(() -> {
     try {
     Thread.sleep(10);
     } catch (InterruptedException e) {
     e.printStackTrace();
     }
     System.out.println(“五号任务” + Thread.currentThread().getName());
     });
     future.get(2, TimeUnit.SECONDS);
     } catch (Exception e) {
     e.printStackTrace();
     } finally {
     threadPool.shutdown();
     }
     }
     }
     源码分析为什么会有区别
     public CompletableFuture thenRun(Runnable action) {
     return uniRunStage(null, action);
     }
     public CompletableFuture thenRunAsync(Runnable action) {
     return uniRunStage(asyncPool, action);
     }
     private static final boolean useCommonPool =
     (ForkJoinPool.getCommonPoolParallelism() > 1);
     /**
     • Default executor – ForkJoinPool.commonPool() unless it cannot
     • support parallelism.
       很明显这里创建了新的线程池返回出去了 ThreadPerTaskExecutor
       */
       private static final Executor asyncPool = useCommonPool ?
       ForkJoinPool.commonPool() : new ThreadPerTaskExecutor();
       4、对计算速度进行选用
       CompletableFuture applyToEither( CompletionStage other, Function fn)
       选取两个线程中最快的线程，作为应用
       public class CompletableFutureFastDemo {
       public static void main(String[] args) {
       CompletableFuture futureA = CompletableFuture.supplyAsync(() -> {
       try {
       TimeUnit.SECONDS.sleep(2);
       } catch (InterruptedException e) {
       e.printStackTrace();
       }
       return “resultA”;
       });
       CompletableFuture futureB = CompletableFuture.supplyAsync(() -> {
       try {
       TimeUnit.SECONDS.sleep(1);
       } catch (InterruptedException e) {
       e.printStackTrace();
       }
       return “resultB”;
       });
       //applyToEither选取一个速度最快的作为应用
       CompletableFuture future = futureA.applyToEither(futureB, f -> {
       try {
       TimeUnit.SECONDS.sleep(1);
       } catch (InterruptedException e) {
       e.printStackTrace();
       }
       return “applyC” + f;
       });
       System.out.println(Thread.currentThread().getName() + “------result:” + future.join());
       }
       }
       5、对计算结果合并
       thenCombine()两个任务CompletionStage任务都完成后，最终指向两个任务的结果一起交给thenCombine来处理
       public class CompletableFutureCombineDemo {
       public static void main(String[] args) {
       CompletableFuture future1 = CompletableFuture.supplyAsync(() -> {
       try {
       Thread.sleep(10);
       } catch (InterruptedException e) {
       e.printStackTrace();
       }
       System.out.println(“任务一执行”);
       return 10;
       });
       CompletableFuture future2 = CompletableFuture.supplyAsync(() -> {
       try {
       Thread.sleep(10);
       } catch (InterruptedException e) {
       e.printStackTrace();
       }
       System.out.println(“任务二执行”);
       return 20;
       });
       CompletableFuture future = future1.thenCombine(future2, (x, y) -> {
       System.out.println(“开始合并”);
       return x + y;
       });
       System.out.println(future.join());
       }
       }