java线程之wait、notifyAll

wait、notifyAll是线程之间用来通信的，设计模式里的观察者模式。

例子，上课前，同学在玩，一个同学观察老师是不是来了，如果来了，叫其他同学坐好。

package com.concurrent;import java.util.HashSet;import java.util.Set;import java.util.concurrent.CountDownLatch;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import junit.framework.TestCase;public class TestWaitNotify extends TestCase {static final CountDownLatch cdl = new CountDownLatch(31);public void testWaitNotify() {Monitor monitor = new Monitor();ExecutorService executorService = Executors.newFixedThreadPool(31);for (int i = 0; i < 30; i++) {Student student = new Student(monitor);monitor.addClassMate(student);executorService.execute(student);}executorService.execute(monitor);System.out.println(Thread.currentThread() + "老师还没来");monitor.setTeacherIsComing(true);System.out.println(Thread.currentThread() + "老师来了");try {cdl.await();} catch (InterruptedException e) {e.printStackTrace();}executorService.shutdown();}static class Student implements Runnable {private Monitor monitor;Student() {}Student(Monitor monitor) {this.monitor = monitor;}@Overridepublic void run() {synchronized (monitor) {while (!monitor.isTeacherIsComing()) {try {monitor.wait();} catch (InterruptedException e) {e.printStackTrace();}}System.out.println(Thread.currentThread() + "回到自己座位，坐下");cdl.countDown();}}}static class Monitor extends Student {private boolean teacherIsComing = false;private Set<Student> classMates = new HashSet<Student>();@Overridepublic void run() {synchronized (this) {while (!teacherIsComing) {System.out.println(Thread.currentThread() + "看老师是否来了");}notifyAll();cdl.countDown();}}public boolean isTeacherIsComing() {return teacherIsComing;}public void setTeacherIsComing(boolean teacherIsComing) {this.teacherIsComing = teacherIsComing;}public void addClassMate(Student student) {classMates.add(student);}}}

运行一下：

Thread[main,5,main]老师还没来Thread[main,5,main]老师来了Thread[pool-1-thread-28,5,main]回到自己座位，坐下Thread[pool-1-thread-29,5,main]回到自己座位，坐下Thread[pool-1-thread-26,5,main]回到自己座位，坐下Thread[pool-1-thread-24,5,main]回到自己座位，坐下Thread[pool-1-thread-22,5,main]回到自己座位，坐下Thread[pool-1-thread-27,5,main]回到自己座位，坐下Thread[pool-1-thread-25,5,main]回到自己座位，坐下Thread[pool-1-thread-23,5,main]回到自己座位，坐下Thread[pool-1-thread-20,5,main]回到自己座位，坐下Thread[pool-1-thread-21,5,main]回到自己座位，坐下Thread[pool-1-thread-19,5,main]回到自己座位，坐下Thread[pool-1-thread-18,5,main]回到自己座位，坐下Thread[pool-1-thread-17,5,main]回到自己座位，坐下Thread[pool-1-thread-16,5,main]回到自己座位，坐下Thread[pool-1-thread-14,5,main]回到自己座位，坐下Thread[pool-1-thread-15,5,main]回到自己座位，坐下Thread[pool-1-thread-12,5,main]回到自己座位，坐下Thread[pool-1-thread-13,5,main]回到自己座位，坐下Thread[pool-1-thread-10,5,main]回到自己座位，坐下Thread[pool-1-thread-11,5,main]回到自己座位，坐下Thread[pool-1-thread-9,5,main]回到自己座位，坐下Thread[pool-1-thread-8,5,main]回到自己座位，坐下Thread[pool-1-thread-7,5,main]回到自己座位，坐下Thread[pool-1-thread-6,5,main]回到自己座位，坐下Thread[pool-1-thread-4,5,main]回到自己座位，坐下Thread[pool-1-thread-5,5,main]回到自己座位，坐下Thread[pool-1-thread-3,5,main]回到自己座位，坐下Thread[pool-1-thread-2,5,main]回到自己座位，坐下Thread[pool-1-thread-1,5,main]回到自己座位，坐下Thread[pool-1-thread-30,5,main]回到自己座位，坐下