CountDownLatch 闭锁的一个简单应用

闭锁：它是一种同步工具类，可以延缓线程的进度，直到其到达终止状态，CountDownLatch 是闭锁的一种实现。

它的常用的两个方法：await 和 countdown

假设初始化 CountdownLatch c=new CountDownLatch(2); 当前线程执行到c.await()时候会阻塞，直到其他线程执行2次c.countdown()，当前线程才解除阻塞。

下面是一个应用：

package cn.concurrent.t10;

import java.util.concurrent.CountDownLatch;

public class CountDownLatcher {

public static void main(String[] args) {

final CountDownLatch step = new CountDownLatch(3);

new Thread(new Runnable() {
public void run() {
try {
Thread.currentThread().sleep(200);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("in onece ready");
step.countDown();
}
}).start();
new Thread(new Runnable() {
public void run() {
try {
Thread.currentThread().sleep(200);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println(" in twoce ready");
step.countDown();
}
}).start();
new Thread(new Runnable() {
public void run() {
try {
Thread.currentThread().sleep(200);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println(" in threece ready");
step.countDown();
}
}).start();

try {
step.await();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("in main ready");
}
}main线程，要等待三个线程都调用了countDown才会执行。