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:
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
原文：https://www.cnblogs.com/zhangfengshi/p/9538954.html
