并发编程学习笔记（六、线程组）

目录：

• 线程组概念
• 一级关联
• 多级关联
• 线程组自动归属特性
• 批量管理线程

线程组概念：

线程组其实就是线程的一个集合，其中可以包含线程，也可以包含线程组，它和树形结构非常相似。

线程组可以有效的组织线程和线程组。

一级关联：

父对象中有子对象，但不存在孙子对象。

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

public class OneLevelDemo {
    public static void main(String[] args) {
        TestThread testThread1 = new TestThread();
        TestThread testThread2 = new TestThread();
        ThreadGroup threadGroup = new ThreadGroup("新建线程组1");
        Thread t0 = new Thread(threadGroup, testThread1);
        Thread t1 = new Thread(threadGroup, testThread2);
        t0.start();
        t1.start();
        System.out.println("活动的线程数为：" + threadGroup.activeCount());
        System.out.println("线程组的名称为：" + threadGroup.getName());
    }
}

多级关联：

父对象中有子对象，也存在孙子对象；但这种级别的线程组是不推荐的，因为维护的成本过高。

public class LevelsDemo {
    public static void main(String[] args) {
        ThreadGroup threadGroup1 = new ThreadGroup("线程组1");
        ThreadGroup threadGroup2
                = new ThreadGroup(threadGroup1, "线程组2");
        ThreadGroup threadGroup3
                = new ThreadGroup(threadGroup1, "线程组3");
        TestThread testThread1 = new TestThread();
        TestThread testThread2 = new TestThread();
        TestThread testThread3 = new TestThread();
        Thread t0 = new Thread(threadGroup1, testThread1);
        Thread t1 = new Thread(threadGroup2, testThread2);
        Thread t2 = new Thread(threadGroup3, testThread3);
        t0.start();
        t1.start();
        t2.start();
        System.out.println("threadGroup1线程组的名称为：" + threadGroup1.getName());
        System.out.println("threadGroup1活动的线程数为：" + threadGroup1.activeCount());
        System.out.println("threadGroup1活动的线程组数为：" + threadGroup1.activeGroupCount());
        System.out.println("threadGroup2线程组的名称为：" + threadGroup2.getName());
        System.out.println("threadGroup2活动的线程数为：" + threadGroup2.activeCount());
        System.out.println("threadGroup3线程组的名称为：" + threadGroup3.getName());
        System.out.println("threadGroup3活动的线程数为：" + threadGroup3.activeCount());
    }
}

线程组自动归属特性：

若线程组未指定则归属到初始化时所处于的线程中。

public class ThreadGroupAuto {
    public static void main(String[] args) {
        System.out.println("当前线程：" + Thread.currentThread().getName() 
                + ", 所属线程组：" + Thread.currentThread().getThreadGroup().getName()
                + ", 线程组中有线程组数量：" + Thread.currentThread().getThreadGroup().activeGroupCount());
        // 没有指定线程组，那么自动归到当前线程所属的线程组中
        ThreadGroup group = new ThreadGroup("新的组");
        System.out.println("线程组中有线程组数量："
                + Thread.currentThread().getThreadGroup().activeGroupCount());
    }
}

批量管理线程：

通过interrupt()方法中断那些长时间还未执行完的线程。

public class BatchThread extends Thread {
    public BatchThread(ThreadGroup tg, String name) {
        super(tg, name);
    }

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

public class ThreadGroupBatchDemo {
    public static void main(String[] args) throws InterruptedException {
        int batch = 5;
        ThreadGroup threadGroup = new ThreadGroup("我的线程组");
        for (int i = 0; i < batch; i++) {
            BatchThread batchThread
                    = new BatchThread(threadGroup, "线程" + i);
            batchThread.start();
        }
        Thread.sleep(10000);
        threadGroup.interrupt();
        System.out.println("调用了ThreadGroup.interrupt()方法");
    }
}