public CountDownLatch(int count) {
        if (count < 0) throw new IllegalArgumentException("count < 0");
        this.sync = new Sync(count);
}
private final Sync sync;
private static final class Sync extends AbstractQueuedSynchronizer {
        private static final long serialVersionUID = 4982264981922014374L;
        Sync(int count) {
            //設(shè)置資源總數(shù)
            setState(count);
        }
        int getCount() {
            return getState();
        }
        protected int tryAcquireShared(int acquires) {
            //資源
            return (getState() == 0) ? 1 : -1;
        }
        protected boolean tryReleaseShared(int releases) {
            // Decrement count; signal when transition to zero
            for (;;) {
                //1、獲取當(dāng)前資源數(shù)
                int c = getState();
                if (c == 0)
                    return false;
                //2、釋放一個資源
                int nextc = c-1;
                //3、CAS更新資源數(shù)
                if (compareAndSetState(c, nextc))
                    return nextc == 0;
            }
        }
    }

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