浅谈sleep、wait、yield、join区别

2023-10-30

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");
            }
        }
    }
}

运行结果：

本文内容由网友自发贡献，版权归原作者所有，本站不承担相应法律责任。如您发现有涉嫌抄袭侵权的内容，请联系:hwhale#tublm.com(使用前将#替换为@)