Java中的CountDownLatch同步工具类使用解析

    public CountDownLatch(int count) {
        if (count < 0) throw new IllegalArgumentException("count < 0");
        this.sync = new Sync(count);
    }

        Sync(int count) {
            setState(count);
        }

    /**
     * 如果count为0时,释放所有的等待线程
     * 如果当前的count比0大就要递减
     * 如果当前count为0什么也不做
     */
    public void countDown() {
        sync.releaseShared(1);
    }

    public final boolean releaseShared(int arg) {
        if (tryReleaseShared(arg)) {
            doReleaseShared();
            return true;
        }
        return false;
    }

protected boolean tryReleaseShared(int releases) {
            // Decrement count; signal when transition to zero
            for (;;) {
                int c = getState();
                if (c == 0)
                    return false;
                int nextc = c-1;
                if (compareAndSetState(c, nextc))
                    return nextc == 0;
            }
        }

    public void await() throws InterruptedException {
        sync.acquireSharedInterruptibly(1);
    }

    public final void acquireSharedInterruptibly(int arg)
            throws InterruptedException {
        if (Thread.interrupted())
            throw new InterruptedException();
        if (tryAcquireShared(arg) < 0)
            doAcquireSharedInterruptibly(arg);
    }

        protected int tryAcquireShared(int acquires) {
            return (getState() == 0) ? 1 : -1;
        }

public static void main(String[] args) throws Exception {
		java.util.concurrent.CountDownLatch c = new java.util.concurrent.CountDownLatch(3);
		ExecutorService es = Executors.newCachedThreadPool();
		for (int i = 0; i < 3; i++) {
			es.execute(new Task(i, c));
		}
		c.await();
		System.out.println("主线程执行任务");
	}
	public static class Task implements Runnable {
		private int m;
		private java.util.concurrent.CountDownLatch c;
		public Task(int m,java.util.concurrent.CountDownLatch c) {
			this.m = m;
			this.c = c;
		}
		@Override
		public void run() {
			System.out.println("子线程"+m+"完成了任务");
			c.countDown();
		}
	}