今天看到深入理解JVM第367页多线程volatile部分照着书本敲着代码发现了一个问题 Thread.activeCount()会一直大于2

public class VolatileTest {public static volatile int race = 0;public static void increase() {    race++;}private static final int THREADS_COUNT = 20;public static void main(String[] args) {    Thread[] threads = new Thread[THREADS_COUNT];    for (int i = 0; i < THREADS_COUNT; i++) {        threads[i] = new Thread(new Runnable() {            @Override            public void run() {                for (int i = 0; i < 10000; i++) {                    increase();                }            }        });        threads[i].start();    }    while (Thread.activeCount() > 1) {        Thread.yield();    }    System.out.println(race);}}

陷入了死循环.......why？

Thread.yield();//应该主线程先让出cpu使用权

问题在这Thread.activeCount() 还有个守护线程！！！所以就会一直陷入无限循环。

加了一句Thread.currentThread().getThreadGroup().list();

while (Thread.activeCount() > 1) {        Thread.currentThread().getThreadGroup().list();        Thread.yield();    }