Android之CountDownLatch线程同步

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CountDownLatch，它维护一个计数器，等待这个CountDownLatch的线程必须等到计数器为0时才可以继续。测试代码如下：

public class CountDownLatchTest {/** * 启动服务器 */public static void startServer() throws Exception {System.out.println("Server is starting.");final CountDownLatch latch = new CountDownLatch(1);new Thread(new Runnable() {@Overridepublic void run() {System.out.println(" Start thread 1");try {Thread.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();}System.out.println(" End thread 1");latch.countDown();}}).start();latch.await();new Thread(new Runnable() {@Overridepublic void run() {System.out.println(" Start thread 2");try {Thread.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();}System.out.println(" End thread 2");}}).start();System.out.println("Server is end!");}public static void main(String[] args) throws Exception {CountDownLatchTest.startServer();}}

运行结果如下：

Server is starting.
Start thread 1
End thread 1
Server is end!
Start thread 2
End thread 2

由上分析，程序首先运行Thread1.并

latch.await();

这时候，当前线程将被进出等待状态，直到latch 中的计数器转减少成0为止。 CountDownLatch中提供了

countDown()

来减少计数器。当计数器的减少到0 的时候，当前线程将被唤醒，所以执行Thread2.