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

 // 調(diào)用 await() 方法的線程會(huì)被掛起，它會(huì)等待直到 count 值為 0 才繼續(xù)執(zhí)行
public void await() throws InterruptedException { };  
// 和 await() 類似，若等待 timeout 時(shí)長(zhǎng)后，count 值還是沒有變?yōu)?0，不再等待，繼續(xù)執(zhí)行
public boolean await(long timeout, TimeUnit unit) throws InterruptedException { };  
// 會(huì)將 count 減 1，直至為 0
public void countDown() {
        sync.releaseShared(1);
    }

 public static void main(String[] args) throws InterruptedException {
        CountDownLatch countDownLatch = new CountDownLatch(1);
        for (int i = 0; i < 5; i++) {
            new Thread(() -> {
                try {
                   //等待
                    countDownLatch.await();
                    String parter = "【" + Thread.currentThread().getName() + "】";
                    System.out.println(parter + "開始執(zhí)行……");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }).start();
        }
        Thread.sleep(2000);
        countDownLatch.countDown();
    }

   public static void main(String[] args) throws Exception {
        CountDownLatch countDownLatch = new CountDownLatch(5);
        for (int i = 0; i < 5; i++) {
            final int index = i;
            new Thread(() -> {
                try {
                    Thread.sleep(1000 +
                            ThreadLocalRandom.current().nextInt(1000));
                    System.out.println(Thread.currentThread().getName()
                            + " finish task" + index);

                    countDownLatch.countDown();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }).start();
        }
        // 主線程在阻塞，當(dāng)計(jì)數(shù)器==0，就喚醒主線程往下執(zhí)行。
        countDownLatch.await();
        System.out.println("主線程:在所有任務(wù)運(yùn)行完成后，進(jìn)行結(jié)果匯總");
    }

 public CountDownLatch(int count) {
        if (count < 0) throw new IllegalArgumentException("count < 0");
        this.sync = new Sync(count);
    }
	    Sync(int count) {
            setState(count);
        }
 protected final void setState(int newState) {
        state = newState;
    }

public void await() throws InterruptedException {
        sync.acquireSharedInterruptibly(1);
    }
 public final void acquireSharedInterruptibly(int arg)
            throws InterruptedException {
        if (Thread.interrupted())
            throw new InterruptedException();
            //arg為1，不為0 ，返回-1，這里小于0
        if (tryAcquireShared(arg) < 0)
        	//入隊(duì)阻塞
            doAcquireSharedInterruptibly(arg);
    }
 protected int tryAcquireShared(int acquires) {
            return (getState() == 0) ? 1 : -1;
        }

private void doAcquireSharedInterruptibly(int arg)
        throws InterruptedException {
        //入隊(duì)，創(chuàng)建節(jié)點(diǎn) 使用共享模式
        final Node node = addWaiter(Node.SHARED);
        boolean failed = true;
        try {
            for (;;) {
            //獲取當(dāng)前節(jié)點(diǎn)的前軀節(jié)點(diǎn)
                final Node p = node.predecessor();
                //如果節(jié)點(diǎn)為head節(jié)點(diǎn)
                if (p == head) {
                	//阻塞動(dòng)作比較重，通常會(huì)再嘗試獲取資源，沒有獲取到返回負(fù)數(shù)
                    int r = tryAcquireShared(arg);
                    if (r >= 0) {
                        setHeadAndPropagate(node, r);
                        p.next = null; // help GC
                        failed = false;
                        return;
                    }
                }
                //判斷是否可以阻塞
                if (shouldParkAfterFailedAcquire(p, node) &&
                    parkAndCheckInterrupt())
                    throw new InterruptedException();
            }
        } finally {
            if (failed)
                cancelAcquire(node);
        }
    }

  public void countDown() {
        sync.releaseShared(1);
    }
  public final boolean releaseShared(int arg) {
        if (tryReleaseShared(arg)) {
            doReleaseShared();
            return true;
        }
        return false;
    }
//嘗試釋放共享鎖
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))
                	//減到0的時(shí)候返回true，進(jìn)行喚醒
                    return nextc == 0;
            }
        }

 private void doReleaseShared() {
        for (;;) {
            Node h = head;
            if (h != null && h != tail) {
                int ws = h.waitStatus;
                if (ws == Node.SIGNAL) {
                	//wa為-1時(shí)，將其狀態(tài)設(shè)置為0，并且喚醒
                    if (!compareAndSetWaitStatus(h, Node.SIGNAL, 0))
                        continue;          
                    unparkSuccessor(h);
                }
                else if (ws == 0 &&
                         !compareAndSetWaitStatus(h, 0, Node.PROPAGATE))
                    continue;                // loop on failed CAS
            }
            if (h == head)                   // loop if head changed
                break;
        }
    }
private void unparkSuccessor(Node node) {
        int ws = node.waitStatus;
        if (ws < 0)
        //ws狀態(tài)小于0就將其設(shè)置為0
            compareAndSetWaitStatus(node, ws, 0);
        Node s = node.next;
        if (s == null || s.waitStatus > 0) {
            s = null;
            for (Node t = tail; t != null && t != node; t = t.prev)
                if (t.waitStatus <= 0)
                    s = t;
        }
        if (s != null)
        //s不為空就調(diào)用unpark
            LockSupport.unpark(s.thread);
    }