Java多线程(4)线程组

Java并发 API里有个有趣的方法是把线程分组。这个方法允许我们按线程组作为一个单位来处理。例如，你有一些线程做着同样的任务，你想控制他们，无论多少线程还在运行，他们的状态会被一个call 中断。

【类比就是你想控制一批人，利用这些线程来完成一些任务，进行统一的管理和监控】

例子：

public class ThreadGroupTest {

    public static void main(String args[]) throws Exception {
        ThreadGroup tg = new ThreadGroup("My Group");
        MyThread thrd = new MyThread(tg, "MyThread #1");
        MyThread thrd2 = new MyThread(tg, "MyThread #2");
        MyThread thrd3 = new MyThread(tg, "MyThread #3");
        thrd.start();
        thrd2.start();
        thrd3.start();
        Thread.sleep(1000);
        System.out.println(tg.activeCount() + " threads in thread group.");
        Thread thrds[] = new Thread[tg.activeCount()];
        tg.enumerate(thrds);
        for (Thread t : thrds)
            System.out.println(t.getName());
        thrd.myStop();
        Thread.sleep(1000);
        System.out.println(tg.activeCount() + " threads in tg.");
        System.out.println(tg.activeCount());
        tg.interrupt();
    }
}


class MyThread extends Thread {
    boolean stopped;
    MyThread(ThreadGroup tg, String name) {
        super(tg, name);
        stopped = false;
    }
    public void run() {
        System.out.println(Thread.currentThread().getName() + " starting.");
        try {
            for (int i = 1; i < 1000; i++) {
                System.out.print(".");
                Thread.sleep(250);
                synchronized (this) {
                    if (stopped)break;
                }
            }
        } catch (Exception exc) {
            System.out.println(Thread.currentThread().getName() + " interrupted.");
        }
        System.out.println(Thread.currentThread().getName() + " exiting.");
    }
    synchronized void myStop() {
        stopped = true;
    }
}

需要说明的是，一旦某个线程加入了一个线程组是不能进行更改的。线程组提供了中断所有进程，返回活动线程数目等相关的API