java Thread yield()方法的理解

时间 2019-12-14

标签 java thread yield 方法理解栏目 Java 繁體版

原文原文链接

先看一下源码 yield()是一个native方法也就是说是C或者C++实现的java

/**
     * A hint to the scheduler that the current thread is willing to yield
     * its current use of a processor. The scheduler is free to ignore this
     * hint.
     *
     * <p> Yield is a heuristic attempt to improve relative progression
     * between threads that would otherwise over-utilise a CPU. Its use
     * should be combined with detailed profiling and benchmarking to
     * ensure that it actually has the desired effect.
     *
     * <p> It is rarely appropriate to use this method. It may be useful
     * for debugging or testing purposes, where it may help to reproduce
     * bugs due to race conditions. It may also be useful when designing
     * concurrency control constructs such as the ones in the
     * {@link java.util.concurrent.locks} package.
     */
    public static native void yield();

概念：当调用Thread.yield()的时候，会给线程调度器一个当前线程愿意出让CPU的使用的暗示，可是线程调度器可能会忽略这个暗示。app

代码ide

public class Demo3 {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i < 10; i++) {
                    System.out.println("当前线程为: "+ Thread.currentThread().getName()+ i);
                    if (i == 5){
                        Thread.yield();
                    }
                }
            }
        };

        Thread thread = new Thread(runnable,"A");
        Thread thread1 = new Thread(runnable,"B");
        thread.start();
        thread1.start();
    }
}

第一次执行结果this

当前线程为: A0
当前线程为: B0
当前线程为: A1
当前线程为: B1
当前线程为: A2
当前线程为: B2
当前线程为: A3
当前线程为: B3
当前线程为: A4
当前线程为: B4
当前线程为: A5
当前线程为: B5
当前线程为: A6
当前线程为: B6
当前线程为: A7
当前线程为: B7
当前线程为: B8
当前线程为: A8
当前线程为: A9
当前线程为: B9
第二次执行结果线程

当前线程为: B0
当前线程为: B1
当前线程为: B2
当前线程为: B3
当前线程为: B4
当前线程为: B5
当前线程为: B6
当前线程为: B7
当前线程为: B8
当前线程为: B9
当前线程为: A0
当前线程为: A1
当前线程为: A2
当前线程为: A3
当前线程为: A4
当前线程为: A5
当前线程为: A6
当前线程为: A7
当前线程为: A8
当前线程为: A9
第三次执行结果debug

当前线程为: A0
当前线程为: A1
当前线程为: A2
当前线程为: A3
当前线程为: A4
当前线程为: A5
当前线程为: A6
当前线程为: A7
当前线程为: A8
当前线程为: A9
当前线程为: B0
当前线程为: B1
当前线程为: B2
当前线程为: B3
当前线程为: B4
当前线程为: B5
当前线程为: B6
当前线程为: B7
当前线程为: B8
当前线程为: B9
第四次执行结果code