闭锁-CountDownLatch

作用:用于一个或多个线程等待其它(一个或多个线程)完成相关操作.像日常生活的门锁一样,比如门装了三把锁,只有当三个把锁都打开时,门才能被打开.

方法:

CountDownLatch(int count)初始化闭锁,指定闩数量.

await();等待通过锁,只有所有的闩都释放后,才能通过锁,阻塞当前线程.

countDown();释放一个闩;

//同 await(),这里指定一个等待超时时间,当到达指定的超时时间后,闩的数量没有减少到0,则返回 false,这里注意当前线程会阻塞指定的超时时间;

//若在指定超时时间内,闩的数量减少到0,会立即返回 true.

boolean await(long timeout, TimeUnit unit);

long getCount();//获取闩的数量,主要用于调试

实现原理:

请参考抽象同步队列(AbstractQueuedSynchronizer)

例子:

 

public class CountDownLatchDemo {

    private static CountDownLatch countDownLatch=new CountDownLatch(100);

    private static int index=0;
    public static void main(String[] args) {
        try {
            for(int i=0;i<5;++i){
                new Thread(){
                    @Override
                    public void run() {
                        try {
                            System.out.println("the thread "+Thread.currentThread().getId()+" pre entry the countdownlatch");
                            countDownLatch.await();
                            System.out.println("the thread "+Thread.currentThread().getId()+" pass the countdonwlatch!");
                        }catch (Throwable throwable){
                            throwable.printStackTrace();
                        }
                    }
                }.start();
            }
            while (index++<100) {
                new Thread() {
                    @Override
                    public void run() {
                        try {
                            Thread.sleep(100);
                        } catch (Throwable throwable) {
                            throwable.printStackTrace();
                        }

                        System.out.println("countdown of thread " + Thread.currentThread().getId());
                        countDownLatch.countDown();
                    }
                }.start();
            }
            System.in.read();
        }catch (Throwable throwable){
            throwable.printStackTrace();
        }


    }
}