多线程系列06-yield()

yield()：线程让步，能让当前线程由“运行状态”进入到“就绪状态”，从而让其他具有相同优先级的等待线程获取执行权。

示例1：

public class ThreadA extends Thread{

    public ThreadA(String name ){
        super(name);
    }

    public synchronized void run(){
        for(int i = 3; i < 9; i++){
            System.out.printf("%s [%d]:%d\n", this.getName(), this.getPriority(), i);
            if(i % 4 == 0){
                Thread.yield();
            }
        }
    }

    public static void main(String[] args) {
        ThreadA t1 = new ThreadA("t1");
        ThreadA t2 = new ThreadA("t2");
        t1.start();
        t2.start();
    }
}

运行结果：

t1 [5]:3
t1 [5]:4
t2 [5]:3
t2 [5]:4
t1 [5]:5
t1 [5]:6
t1 [5]:7
t1 [5]:8
t2 [5]:5
t2 [5]:6
t2 [5]:7
t2 [5]:8

示例二：

public class YieldLockTest {

    private static Object obj = new Object();

    static class ThreadA extends Thread{
        public ThreadA(String name){
            super(name);
        }

        public void run(){
            synchronized (obj){
                for(int i = 3; i < 8; i++){
                    System.out.printf("%s [%d]:%d\n", this.getName(), this.getPriority(), i);
                    if(i % 3 == 0){
                        Thread.yield();
                    }
                }
            }
        }

        public static void main(String[] args) {
           ThreadA thread1 = new ThreadA("thread1");
           ThreadA thread2 = new ThreadA("thread2");

           thread1.start();
           thread2.start();
        }

    }
}

运行结果：

thread1 [5]:3
thread1 [5]:4
thread1 [5]:5
thread1 [5]:6
thread1 [5]:7
thread2 [5]:3
thread2 [5]:4
thread2 [5]:5
thread2 [5]:6
thread2 [5]:7

结果说明：
(01) wait()是让线程由“运行状态”进入到“等待(阻塞)状态”，yield()是让线程由“运行状态”进入到“就绪状态”。
(02) wait()是会线程释放它所持有对象的同步锁，而yield()方法不会释放锁。