CountDownLatch 可以用排他锁来实现吗？

Question

JDK1.8的源码是通过AQS共享锁实现的，使用共享锁有哪些注意事项？为什么不使用排他锁？下面附上我的排他锁实现的代码：

public class MyCountDownLatch {
private static final class Sync extends AbstractQueuedSynchronizer {
    Sync(int count) {
        setState(count);
    }
    int getCount() {
        return getState();
    }
    protected boolean tryAcquire(int acquires) {
        return (getState() == 0) ? true :false;
    }
    protected boolean tryRelease(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;
        }
    }
}
private final MyCountDownLatch.Sync sync;
public MyCountDownLatch(int count) {
    this.sync = new MyCountDownLatch.Sync(count);
}
public void await() throws InterruptedException {
    sync.acquireInterruptibly(1);
}
public void countDown() {
    sync.release(1);
}
public static void main(String[] args) throws InterruptedException {
    MyCountDownLatch myCountDownLatch = new MyCountDownLatch(5);
    for(int i=0;i<5;i++){
        new Thread(()-> {
            try {
                Thread.sleep(200);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName()+"start");
            myCountDownLatch.countDown();
        }).start();
    }
    myCountDownLatch.await();
    System.out.println("finished");

}

}

Answer 1

好吧，shared lock 的意思是，您可以有超过 1 个线程等待完成。如果您使用exclusive lock 实现它，那么您将只能等待 1 个线程。