android 并发CountDownLatch、Semaphore和CyclicBarrier

CountDownLatch

介绍

CountDownLatch是一个计数器闭锁，通过它可以完成类似于阻塞当前线程的功能。CountDownLatch 用一个计数器进行初始化，线程调用await函数等待 CountDownLatch的计数器减为0后，才能继续执行。而计数器如何减为0呢？其他线程通过调用countDown函数，减少计数器。

代码

 private void countDownLatchTest() {
        TAG = "countDownLatchTest";
        ExecutorService executorService = Executors.newCachedThreadPool();
        final CountDownLatch countDownLatch = new CountDownLatch(threadCount);

        for (int i = 0; i < threadCount; i++) {
            final int threadNum = I;
            executorService.execute(new Runnable() {
                @Override
                public void run() {
                    try {
                        RunTest(threadNum);
                    } catch (Exception e) {
                        e.printStackTrace();
                    } finally {
                        countDownLatch.countDown();
                    }

                }
            });
        }
        try {
            countDownLatch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        Log.d(TAG, "finish");
        executorService.shutdown();
    }

    private void RunTest(int threadNum) throws Exception {
        Thread.sleep(100);
        Log.d(TAG, Integer.toString(threadNum));
        Thread.sleep(100);
    }

打印信息

image.png

从打印信息看到 finish是在threadNum变为0之后才打印的。

Semaphore