一.简介:
Latch意思是:门闩的意思,形象的来说await就是拴上门闩,等到门闩释放后当前线程开始工作。
下面是来自简书上的解释:
CountDownlatch
是一个多功能的同步工具,可以被用于各种目的。一个CountDownLatch
通过一个值为1的count
被初始化,来作为一个开/关的门或门闩:所有调用了await()
的线程都会在门前等待,直到门被一个线程通过调用countDown()
打开。一个被初始化为N的CountDownLatch
可以被用来“在N个线程都完成了某种操作(或者一些操作已经被完成了N次)之后创建一个线程”。
CountDownLatch
一个有用的属性就是它不需要线程们在继续执行之前,调用countDown
来等待count
被减到0。它简单地阻止了任何调用了await()
的线程继续,直到所有的线程都能够通过。
import java.util.concurrent.CountDownLatch; /** * Created by cuijunyong on 2018/2/3. */ public class Xunhuan { public static int i = 0; private static final CountDownLatch end = new CountDownLatch(2); private static final CountDownLatch start = new CountDownLatch(1); public static void main(String[] args) throws Exception{ A a = new A(); // A b = new A(); MyThread myThread = new MyThread(); Thread b = new Thread(myThread); // Thread[] threads = new Thread[10]; // for(int x = 0; x < threads.length; x++){ // threads[i] = new Thread(myThread); // threads[i].start(); // } a.start(); b.start(); System.out.println("开始工作了\n"); start.countDown(); end.await(); System.out.println("a:" + a.isAlive()); System.out.println("b:" +b.isAlive()); System.out.println("i=" + i); } static class MyThread implements Runnable{ public void run() { // int i = 0; try { start.await(); int j = 0; while (j < 100){ j++; i++; System.out.println("B = " + i); } System.out.println("end.count = " + end.getCount()); end.countDown(); } catch (Exception e) { e.printStackTrace(); } } } static class A extends Thread{ @Override public void run() { // int i = 0; try { start.await(); int j = 0; while (j < 100){ j++; i++; System.out.println("A = " + i); } System.out.println("end.count = " + end.getCount()); end.countDown(); } catch (Exception e) { e.printStackTrace(); } } } }
结果:前面略略略
A = 190 A = 191 A = 192 A = 193 A = 194 A = 195 B = 171 end.count = 2 B = 196 B = 197 B = 198 B = 199 B = 200 end.count = 1 a:false b:false i=200