线程组

线程组可以批量管理线程和线程组对象。

一级关联

例子如下，建立一级关联。

public class MyThread43 implements Runnable{
    public void run()
    {
        try
        {
            while (!Thread.currentThread().isInterrupted())
            {
                System.out.println("ThreadName = " + Thread.currentThread().getName());
                Thread.sleep(3000);
            }
        }
        catch (InterruptedException e)
        {
            e.printStackTrace();
        }
    }

    public static void main(String[] args)
    {
        MyThread43 mt0 = new MyThread43();
        MyThread43 mt1 = new MyThread43();
        ThreadGroup tg = new ThreadGroup("新建线程组1");
        Thread t0 = new Thread(tg, mt0);
        Thread t1 = new Thread(tg, mt1);
        t0.start();
        t1.start();
        System.out.println("活动的线程数为：" + tg.activeCount());
        System.out.println("线程组的名称为：" + tg.getName());
    }
}

输出结果如下

活动的线程数为：2
线程组的名称为：新建线程组1
ThreadName = Thread-0
ThreadName = Thread-1
ThreadName = Thread-0
ThreadName = Thread-1
ThreadName = Thread-1
ThreadName = Thread-0
ThreadName = Thread-1
ThreadName = Thread-0
······

每隔三秒输出两个线程名称，符合预期。

线程组自动归组属性

public class ThreadDomain49 {
    public static void main(String[] args) {
        System.out.println("A处线程：" + Thread.currentThread().getName() + ", 所属线程：" + Thread.currentThread().getThreadGroup().getName() +
                ", 组中有线程组数量：" + Thread.currentThread().getThreadGroup().activeGroupCount());
        ThreadGroup group = new ThreadGroup("新的组");
        System.out.println("B处线程：" + Thread.currentThread().getName() + ", 所属线程：" + Thread.currentThread().getThreadGroup().getName() +
                ", 组中有线程组数量：" + Thread.currentThread().getThreadGroup().activeGroupCount());
        ThreadGroup[] tg = new ThreadGroup[Thread.currentThread().getThreadGroup().activeGroupCount()];
        Thread.currentThread().getThreadGroup().enumerate(tg);
        for (int i = 0; i < tg.length; i++)
            System.out.println("第一个线程组名称为：" + tg[i].getName());
    }
}

输出结果如下

A处线程：main, 所属线程：main, 组中有线程组数量：0
B处线程：main, 所属线程：main, 组中有线程组数量：1
第一个线程组名称为：新的组

没有指定线程组，则归属到当前线程所属的组。

根线程组

public class ThreadDomain50 {


    public static void main(String[] args)
    {
        System.out.println(Thread.currentThread().getThreadGroup().getParent().getName());
        System.out.println(Thread.currentThread().getThreadGroup().getParent().getParent().getName());
    }


}

运行结果

system
Exception in thread "main" java.lang.NullPointerException
    at com.advance.MultiThread3.MyThread.ThreadDomain50.main(ThreadDomain50.java:14)

当前线程的线程组的父线程组是系统线程组；系统线程组的父线程组不存在；系统线程组就是根线程组。

批量停止组内线程
请看示例

public class MyThread44 extends Thread{

    public MyThread44(ThreadGroup tg, String name)
    {
        super(tg, name);
    }

    public void run()
    {
        System.out.println("ThreadName = " + Thread.currentThread().getName() +
                "准备开始死循环了");
        while (!this.isInterrupted()){}
        System.out.println("ThreadName = " + Thread.currentThread().getName() +
                "结束了");
    }

    public static void main(String[] args) throws InterruptedException {
        ThreadGroup tg = new ThreadGroup("我的线程组");
        MyThread44 mt = null;
        for (int i = 0; i < 3; i++)
        {
            mt = new MyThread44(tg, "线程" + i);
            mt.start();
        }
        Thread.sleep(5000);
        tg.interrupt();
        System.out.println("调用了interrupt()方法");
    }
}

输出结果如下

ThreadName = 线程0准备开始死循环了
ThreadName = 线程1准备开始死循环了
ThreadName = 线程2准备开始死循环了
调用了interrupt()方法
ThreadName = 线程0结束了
ThreadName = 线程2结束了
ThreadName = 线程1结束了

可以看到，ThreadGroup的interrupt方法批量中断线程组的线程。