线程sleep、wait、yield、join区别

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我是靠谱客的博主明亮小笼包，最近开发中收集的这篇文章主要介绍线程sleep、wait、yield、join区别，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

sleep

sleep 方法是属于 Thread 类中的，sleep 过程中线程不会释放锁，只会阻塞线程，让出cpu给其他线程，但是他的监控状态依然保持着，当指定的时间到了又会自动恢复运行状态，可中断，sleep 给其他线程运行机会时不考虑线程的优先级，因此会给低优先级的线程以运行的机会

示例代码：

    /**
     * 线程sleep测试
     *
     * @author supu
     * @date 2019-07-01 9:59
     **/
    public class ThreadSleepTest {
        private static final Object obj = new Object();

        public static void main(String[] args) {
            Thread t1 = new Thread(new MyThread1());
            Thread t2 = new Thread(new MyThread2());
            t1.start();
            t2.start();
        }

        static class MyThread1 implements Runnable {

            @Override
            public void run() {
                synchronized (obj) {
                    System.out.println("thread1 start");
                    try {
                        Thread.sleep(500);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println("thread1 end");
                }
            }
        }

        static class MyThread2 implements Runnable {

            @Override
            public void run() {
                synchronized (obj) {
                    System.out.println("thread2 start");
                    System.out.println("thread2 end");
                }
            }
        }
    }

运行结果：

wait

wait 方法是属于 Object 类中的，wait 过程中线程会释放对象锁，只有当其他线程调用 notify 才能唤醒此线程。wait 使用时必须先获取对象锁，即必须在 synchronized 修饰的代码块中使用，那么相应的 notify 方法同样必须在 synchronized 修饰的代码块中使用，如果没有在synchronized 修饰的代码块中使用时运行时会抛出IllegalMonitorStateException的异常

示例代码：

    package com.springboot.demo.thread;

    /**
     * 线程wait测试类
     *
     * @author supu
     * @date 2019-06-28 17:35
     **/
    public class ObjectWaitTest {
        private static final Object obj = new Object();

        public static void main(String[] args) {
            Thread t1 = new Thread(new MyThread1());
            Thread t2 = new Thread(new MyThread2());
            t1.start();
            t2.start();
        }

        static class MyThread1 implements Runnable {

            @Override
            public void run() {
                synchronized (obj) {
                    System.out.println("thread1 start");
                    try {
                        obj.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println("thread1 end");
                }
            }
        }

        static class MyThread2 implements Runnable {

            @Override
            public void run() {
                synchronized (obj) {
                    System.out.println("thread2 start");
                    obj.notify();
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println("thread2 end");
                }
            }
        }
    }

运行结果：

yield

和 sleep 一样都是 Thread 类的方法，都是暂停当前正在执行的线程对象，不会释放资源锁，和 sleep 不同的是 yield方法并不会让线程进入阻塞状态，而是让线程重回就绪状态，它只需要等待重新获取CPU执行时间，所以执行yield()的线程有可能在进入到可执行状态后马上又被执行。还有一点和 sleep 不同的是 yield 方法只能使同优先级或更高优先级的线程有执行的机会

示例代码：

    package com.springboot.demo.thread;

    /**
     * yield测试
     *
     * @author supu
     * @date 2019-06-28 18:02
     **/
    public class ThreadYieldTest {
        private static final Object obj = new Object();

        public static void main(String[] args) {
            Thread t3 = new Thread(new MyThread3());
            Thread t1 = new Thread(new MyThread1());
            Thread t2 = new Thread(new MyThread2());
            t3.start();
            t1.start();
            t2.start();
        }

        static class MyThread1 implements Runnable {

            @Override
            public void run() {
                synchronized (obj) {
                    System.out.println("thread1 start");
                    Thread.yield();
                    System.out.println("thread1 end");
                }
            }
        }

        static class MyThread2 implements Runnable {

            @Override
            public void run() {
                synchronized (obj) {
                    System.out.println("thread2 start");
                    System.out.println("thread2 end");
                }
            }
        }

        static class MyThread3 implements Runnable {

            @Override
            public void run() {
                System.out.println("thread3 start");
                Thread.yield();
                System.out.println("thread3 end");
            }
        }
    }

运行结果：

join

等待调用join方法的线程结束之后，程序再继续执行，一般用于等待异步线程执行完结果之后才能继续运行的场景。例如：主线程创建并启动了子线程，如果子线程中药进行大量耗时运算计算某个数据值，而主线程要取得这个数据值才能运行，这时就要用到 join 方法了

示例代码：

    package com.springboot.demo.thread;

    /**
     * 线程join测试
     *
     * @author supu
     * @date 2019-07-01 11:01
     **/
    public class ThreadJoinTest {
        private static final Object obj = new Object();
        private static int count = 0;

        public static void main(String[] args) {
            Thread t1 = new Thread(new MyThread1());
            Thread t2 = new Thread(new MyThread2());
            t1.start();
            t2.start();
            try {
                t1.join();
                t2.join();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("count:" + count);
        }

        static class MyThread1 implements Runnable {

            @Override
            public void run() {
                synchronized (obj) {
                    System.out.println("thread1 start");
                    for (int i = 0; i < 10; i++){
                        count++;
                    }
                    try {
                        Thread.sleep(500);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println("thread1 end");
                }
            }
        }

        static class MyThread2 implements Runnable {

            @Override
            public void run() {
                synchronized (obj) {
                    System.out.println("thread2 start");
                    try {
                        Thread.sleep(500);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    for (int i = 0; i < 10; i++){
                        count++;
                    }
                    System.out.println("thread2 end");
                }
            }
        }
    }