详解Java CountDownLatch完成异步回调实例

publicclassAsyncDemo {

  privatestaticvoiddoSomeTask() {

    System.out.println("Hello World");

  }

  privatestaticvoidonCompletion() {

    System.out.println("All tasks finished");

  }

  publicstaticvoidmain(String[] args) {

    ExecutorService executor = Executors.newCachedThreadPool();

    finalCountDownLatch latch =newCountDownLatch(2);

    executor.execute(newTask(latch));

    executor.execute(newTask(latch));

    executor.execute(() -> {

      try{

        latch.await();

      }catch(InterruptedException e) {

        e.printStackTrace();

      }

      onCompletion();

    });

    executor.shutdown();

  }

  privatestaticclassTaskimplementsRunnable {

    /**

     * CountDownLatch 是JDK提供的一个简单的线程监测工具

     * 基于简单的计数，调用countDown()方法表明当前线程已经终止

     * 在监测线程中调用await()方法,该方法会一直挂起直到所有其它线程终止

     */

    privatefinalCountDownLatch latch;

    publicTask(CountDownLatch latch) {

      this.latch = latch;

    }

    @Override

    publicvoidrun() {

      try{

        doSomeTask();

      }catch(Exception e) {

        e.printStackTrace();

      }finally{

        latch.countDown();

      }

    }

  }

}