CountDownLatch(int count); //構(gòu)造方法，創(chuàng)建一個(gè)值為count 的計(jì)數(shù)器。
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await();//阻塞當(dāng)前線(xiàn)程，將當(dāng)前線(xiàn)程加入阻塞隊(duì)列。
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await(long timeout, TimeUnit unit);//在timeout的時(shí)間之內(nèi)阻塞當(dāng)前線(xiàn)程,時(shí)間一過(guò)則當(dāng)前線(xiàn)程可以執(zhí)行，
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countDown();//對(duì)計(jì)數(shù)器進(jìn)行遞減1操作，當(dāng)計(jì)數(shù)器遞減至0時(shí)，當(dāng)前線(xiàn)程會(huì)去喚醒阻塞隊(duì)列里的所有線(xiàn)程。

  public static void main(String[] args) {
        CountDownLatch count = new CountDownLatch(3);
        Thread thread = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep((int)(Math.random()*1000));
                    System.out.println("獲取接口一的數(shù)據(jù)");
                    count.countDown();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
        Thread thread2 = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep((int)(Math.random()*1000));
                    System.out.println("獲取接口二的數(shù)據(jù)");
                    count.countDown();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
        Thread thread3 = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep((int)(Math.random()*1000));
                    System.out.println("獲取接口三的數(shù)據(jù)");
                    count.countDown();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
        thread.start();
        thread2.start();
        thread3.start();
        try {
            count.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("執(zhí)行成功");
    }

  public CountDownLatch(int count) {
        if (count < 0) throw new IllegalArgumentException("count < 0");
        this.sync = new Sync(count);//創(chuàng)建同步隊(duì)列，并設(shè)置初始計(jì)數(shù)器值
    }

    private static final class Sync extends AbstractQueuedSynchronizer {
        private static final long serialVersionUID = 4982264981922014374L;
        Sync(int count) {
            setState(count);
        }
        int getCount() {
            return getState();
        }
        protected int tryAcquireShared(int acquires) {
            return (getState() == 0) ? 1 : -1;
        }
        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);
}

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

private void doAcquireSharedInterruptibly(int arg)
        throws InterruptedException {
        //新建節(jié)點(diǎn)加入阻塞隊(duì)列
        final Node node = addWaiter(Node.SHARED);
        boolean failed = true;
        try {
            for (;;) {
                //獲得當(dāng)前節(jié)點(diǎn)pre節(jié)點(diǎn)
                final Node p = node.predecessor();
                if (p == head) {
                    int r = tryAcquireShared(arg);//返回鎖的state
                    if (r >= 0) {
                        setHeadAndPropagate(node, r);
                        p.next = null; // help GC
                        failed = false;
                        return;
                    }
                }
                //重組雙向鏈表，清空無(wú)效節(jié)點(diǎn)，掛起當(dāng)前線(xiàn)程
                if (shouldParkAfterFailedAcquire(p, node) &&
                    parkAndCheckInterrupt())
                    throw new InterruptedException();
            }
        } finally {
            if (failed)
                cancelAcquire(node);
        }
    }

public void countDown() {
        //遞減鎖重入次數(shù)，當(dāng)state=0時(shí)喚醒所有阻塞線(xiàn)程
        sync.releaseShared(1);
    }

public final boolean releaseShared(int arg) {
        //遞減鎖的重入次數(shù)
        if (tryReleaseShared(arg)) {
            doReleaseShared();//喚醒隊(duì)列所有阻塞的節(jié)點(diǎn)
            return true;
        }
        return false;
    }
 private void doReleaseShared() {
        //喚醒所有阻塞隊(duì)列里面的線(xiàn)程
        for (;;) {
            Node h = head;
            if (h != null && h != tail) {
                int ws = h.waitStatus;
                if (ws == Node.SIGNAL) {//節(jié)點(diǎn)是否在等待喚醒狀態(tài)
                    if (!compareAndSetWaitStatus(h, Node.SIGNAL, 0))//修改狀態(tài)為初始
                        continue;
                    unparkSuccessor(h);//成功則喚醒線(xiàn)程
                }
                else if (ws == 0 &&
                         !compareAndSetWaitStatus(h, 0, Node.PROPAGATE))
                    continue;                // loop on failed CAS
            }
            if (h == head)                   // loop if head changed
                break;
        }
    }