多线程(七同步计数器-CountDownLatch)
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CountDownLatch是一个线程的同步计数器,主要有2个使用场景。1、作为一个开关,N个子线程准备就绪,等待主线程的放行,然后子线程一起开始执行。
Task
package com.jane;
import java.util.concurrent.CountDownLatch;
public class Task implements Runnable
private CountDownLatch countDownLatch;
private String name;
public Task(CountDownLatch countDownLatch, String name)
this.countDownLatch = countDownLatch;
this.name = name;
@Override
public void run()
try
System.out.println(name + "开始等待开关......");
countDownLatch.await();
catch (InterruptedException e)
e.printStackTrace();
System.out.println(name + "执行任务完成");
主线程
public class Main
public static void main(String[] args) throws InterruptedException
//主线程创建,和子线程共享
CountDownLatch countDownLatch = new CountDownLatch(1);
System.out.println("主线程启动......");
//创建3个子线程
Thread t1 = new Thread(new Task(countDownLatch, "线程-1"));
Thread t2 = new Thread(new Task(countDownLatch, "线程-2"));
Thread t3 = new Thread(new Task(countDownLatch, "线程-3"));
t1.start();
t2.start();
t3.start();
Thread.sleep(2000);
System.out.println("主线程执行任务完毕,放行......");
countDownLatch.countDown();
System.out.println("主线程执行完毕");
执行结果
2、主线程等待N个子线程的处理结果,子线程都完成后,主线程继续执行。
Task
package com.jane;
import java.util.concurrent.CountDownLatch;
public class Task1 implements Runnable
private CountDownLatch countDownLatch;
private String name;
public Task1(CountDownLatch countDownLatch, String name)
this.countDownLatch = countDownLatch;
this.name = name;
@Override
public void run()
try
System.out.println(name + "开始开始执行任务......");
Thread.sleep(2000);
System.out.println(name + "执行任务完成");
countDownLatch.countDown();
catch (Exception e)
e.printStackTrace();
主线程
package com.jane;
import java.util.concurrent.CountDownLatch;
public class Main1
public static void main(String[] args) throws InterruptedException
//主线程创建,和子线程共享
CountDownLatch countDownLatch = new CountDownLatch(3);
System.out.println("主线程启动......");
//创建3个子线程
Thread t1 = new Thread(new Task1(countDownLatch, "线程-1"));
Thread t2 = new Thread(new Task1(countDownLatch, "线程-2"));
Thread t3 = new Thread(new Task1(countDownLatch, "线程-3"));
t1.start();
t2.start();
t3.start();
System.out.println("主线程等待子线程执行结果......");
countDownLatch.await();
System.out.println("主线程执行完毕");
执行结果
注意:CountDownLatch的计数只能使用一次,不会自动重新开始。
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