Java并发编程之CountDownLatch解读

//参数count为计数值
public CountDownLatch(int count) {  };  

//调用await()方法的线程会被挂起，它会等待直到count值为0才继续执行
public void await() throws InterruptedException { };   
//和await()类似，只不过等待一定的时间后count值还没变为0的话就会继续执行
public boolean await(long timeout, TimeUnit unit) throws InterruptedException { };  
//将count值减1
public void countDown() { };  

public class KaneCountDownLatch {
    private KaneCountDownLatch.Sync sync;
    public KaneCountDownLatch(int count) {
        this.sync = new KaneCountDownLatch.Sync(count);
    }
    public void countDown() {
        this.sync.releaseShared(1);
    }
    public void await() {
        this.sync.acquireShared(1);
    }
    class Sync extends AbstractQueuedSynchronizer {
        public Sync(int count) {
            this.setState(count);
        }
        protected int tryAcquireShared(int arg) {
            return this.getState() == 0 ? 1 : -1;
        }
        protected boolean tryReleaseShared(int arg) {
            int c;
            int nextc;
            do {
                c = this.getState();
                if (c == 0) {
                    return false;
                }
                nextc = c - 1;
            } while(!this.compareAndSetState(c, nextc));
            return nextc == 0;
        }
    }
}

public class CountDownLatch_Demo {
    public static void main(String[] args) throws InterruptedException {
        KaneCountDownLatch latch = new KaneCountDownLatch(6); //计数为6
        for (int i = 0; i <6 ; i++) {
            new Thread(()->{
                System.out.println("开始准备.....");
                latch.countDown();//计数减一
            }).start();
            Thread.sleep(1000);
        }
        latch.await(); //每个线程执行一次，则-1，在latch为0的时候开始向下运行 这是这些线程都准备就绪，然后去一起干同一件事
        //还有一种方式， 将一个活分为多段，每个线程去干一段
//        for (int i = 0; i <6 ; i++) {
//            new Thread(()->{
//                  latch.countDown(); // 计数减一
//                try {
//                    latch.await(); // 阻塞 -- > 0
//                    System.out.println("线程："+Thread.currentThread().getName()+"执行完毕");
//                } catch (InterruptedException e) {
//                    e.printStackTrace();
//                }
//            }).start();
//        }
        System.out.println("开始干活....");
    }
}