Thread.yeild方法详解

Thread.yeild方法详解

从原理上讲其实Thread.yeild方法其实只是给线程调度机制一个暗示：我的任务处理的差不多了，可以让给相同优先级的线程CPU资源了；不过确实只是一个暗示，没有任何机制保证它的建议将被采纳；

看一个例子就知道了；

public class LiftOff implements Runnable {

    protected int countDown = 5;

    private static int taskCount = 0;

    private final int id = taskCount++;

    public LiftOff() {

    }

    public LiftOff(int countDown) {

        this.countDown = countDown;

    }

    public String status() {

        // System.out.println(Thread.currentThread().getName());

        return Thread.currentThread().getName() + "#" + id + "(" + (countDown > 0 ? countDown + ")" : "Liftoff!" + ")");

    }

    @Override

    public void run() {

        // TODO Auto-generated method stub

        /*

         * --countDown：先减去，再赋值

         * countDown--先赋值，再减去

         */

        while (countDown-- > 0) {

            System.out.println(status());

            Thread.yield();// 让步【表示我的任务处理的差不多了，可以让步给其他线程资源了】；CPU资源给其他线程使用；t.join当前线程挂起，直到t线程调用结束后切回

            /*

             * try {

             * TimeUnit.MILLISECONDS.sleep(100);

             * } catch (InterruptedException e) {

             * // TODO Auto-generated catch block

             * // e.printStackTrace();

             * System.err.println("异常终止...");

             * }

             */

        }

    }

public class ExecuteMethodPool {

    public static void main(String[] args) {

        ExecutorService executorService = Executors.newCachedThreadPool();// 无界队列：将为每个任务创建一个线程

        // ExecutorService executorService = Executors.newFixedThreadPool(2);// 有限线程数队列

        // ExecutorService executorService = Executors.newSingleThreadExecutor();// 有限线程数队列

        for (int i = 0; i < 3; i++) {

            executorService.execute(new LiftOff());

        }

        executorService.shutdown();

    }

}

响应结果打印:

p.p1 { margin: 0; font: 12px Menlo }

pool-1-thread-2#1(4)

pool-1-thread-1#0(4)

pool-1-thread-3#2(4)

pool-1-thread-2#1(3)

pool-1-thread-3#2(3)

pool-1-thread-3#2(2)

pool-1-thread-1#0(3)

pool-1-thread-2#1(2)

pool-1-thread-3#2(1)

pool-1-thread-1#0(2)

pool-1-thread-2#1(1)

pool-1-thread-3#2(Liftoff!)

pool-1-thread-1#0(1)

pool-1-thread-2#1(Liftoff!)

pool-1-thread-1#0(Liftoff!)

以上标注的两个一样的线程先后执行 并没有遵守yeild给线程调度的建议