//減少鎖存器的計(jì)數(shù)，如果計(jì)數(shù)達(dá)到零，則釋放所有等待線程。 
//計(jì)數(shù)器 
public void countDown() { 
    sync.releaseShared(1); 
} 
//導(dǎo)致當(dāng)前線程等待，直到鎖存器遞減至零為止，除非該線程被中斷。 
//火鍋店調(diào)用await的線程，count為0才能繼續(xù)執(zhí)行 
public void await() throws InterruptedException { 
    sync.acquireSharedInterruptibly(1); 
}

//count 數(shù)量，理解為小伙伴的個(gè)數(shù) 
public CountDownLatch(int count) { 
    if (count < 0) throw new IllegalArgumentException("count < 0"); 
        this.sync = new Sync(count); 
} 
//獲取剩余的數(shù)量 
public long getCount() { 
    return sync.getCount(); 
}

public boolean await(long timeout, TimeUnit unit) throws InterruptedException { 
    return sync.tryAcquireSharedNanos(1, unit.toNanos(timeout)); 
} 
//當(dāng)狀態(tài)不為0掛起，表示當(dāng)前線程被占有，需要線程排隊(duì) 
protected int tryAcquireShared(int acquires) { 
    return (getState() == 0) ? 1 : -1; 
} 
//在共享模式下獲取 
doAcquireSharedInterruptibly(int arg)

public void countDown() { 
    sync.releaseShared(1); 
} 
protected boolean tryReleaseShared(int releases) { 
// Decrement count; signal when transition to zero 
//自旋防止失敗 
    for (;;) { 
        //獲取狀態(tài)
        int c = getState(); 
        //狀態(tài)為為0返回false，表示沒有被線程占有 
        if (c == 0) return false; 
        //調(diào)用cas來進(jìn)行替換，也保證了線程安全，當(dāng)為0的時(shí)候喚醒 
        int nextc = c-1; 
        if (compareAndSetState(c, nextc)) 
            return nextc == 0; 
    } 
} 
//當(dāng)任務(wù)數(shù)量為0，aqs的釋放共享鎖 
void doReleaseShared()

private void doReleaseShared() {
    /*
        * Ensure that a release propagates, even if there are other
        * in-progress acquires/releases.  This proceeds in the usual
        * way of trying to unparkSuccessor of head if it needs
        * signal. But if it does not, status is set to PROPAGATE to
        * ensure that upon release, propagation continues.
        * Additionally, we must loop in case a new node is added
        * while we are doing this. Also, unlike other uses of
        * unparkSuccessor, we need to know if CAS to reset status
        * fails, if so rechecking.
        */
    // 無限循環(huán)
    for (;;) {
        // 保存頭節(jié)點(diǎn)
        Node h = head;
        // 頭節(jié)點(diǎn)不為空并且頭節(jié)點(diǎn)不為尾結(jié)點(diǎn)
        if (h != null && h != tail) { 
            // 獲取頭節(jié)點(diǎn)的等待狀態(tài)
            int ws = h.waitStatus; 
            if (ws == Node.SIGNAL) { 
                // 狀態(tài)為SIGNAL,CAS更新狀態(tài)
                if (!compareAndSetWaitStatus(h, Node.SIGNAL, 0)) 
                    continue;            // loop to recheck cases
                // 釋放后繼結(jié)點(diǎn)
                unparkSuccessor(h);
            }
            // 狀態(tài)為0并且更新不成功，繼續(xù)
            else if (ws == 0 &&
                        !compareAndSetWaitStatus(h, 0, Node.PROPAGATE)) // 
                continue;                // loop on failed CAS
        }
        if (h == head) // 若頭節(jié)點(diǎn)改變，繼續(xù)循環(huán)  
            break;
    }
}

public class CountDownLatchTest {
    private static Lock lock = new ReentrantLock();
    private static CountDownLatch countDownLatch = new CountDownLatch(4);
    public static void main(String[] args) {
        ExecutorService executorService = Executors.newFixedThreadPool(4);
        IntStream.range(0,16).forEach(i ->{
            executorService.submit(()->{
                lock.lock();
                System.out.println(Thread.currentThread().getName()+ "來火鍋店吃火鍋！");
                try {
                    Thread.sleep(1000);
                    countDownLatch.countDown();
                    System.out.println(Thread.currentThread().getName() + "我到火鍋店了，準(zhǔn)備開吃！");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    lock.unlock();
                }
            });
        });
        try {
            countDownLatch.await(5,TimeUnit.SECONDS);
            System.out.println("人到齊了，開飯");
            executorService.shutdown();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

public class CountDownLatchTest2 {
    private static Lock lock = new ReentrantLock();
    private static CountDownLatch countDownLatch = new CountDownLatch(1);
    public static void main(String[] args) {
        ExecutorService executorService = Executors.newFixedThreadPool(4);
        IntStream.range(0,4).forEach(i ->{
            executorService.submit(()->{
                System.out.println(Thread.currentThread().getName()+ "準(zhǔn)備開始搶位子！");
                try {
                    //Thread.sleep(1000);
                    countDownLatch.await();
                    System.out.println(Thread.currentThread().getName() + "搶到了位置");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            });
        });
        try {
            Thread.sleep(5000);
            System.out.println("五秒后開始搶位置");
            countDownLatch.countDown();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        executorService.shutdown();
    }
}