3，ThreadGroup 的使用场景以及用法

1 一个大型任务，可分成多个独立的子线程并发进行，最后等待所有的子线程执行结束然后继续往下执行，

使用场景比如

要查找某个用户的最近三个月的通话记录，起 3 个子线程，分别查找最近三个月的记录，然后通过

                int activeCount = tgroup.activeCount();
                while ( activeCount >  ) {
                    System.out.println("activeCount=" + activeCount );
                    try {
                        Thread.sleep();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    activeCount = tgroup.activeCount();
                }

阻塞住主线程，直到三个子线程全部执行结束，activeCount() == 0，继续玩下执行

2，一个大型任务，可分成多个独立的子线程并发进行，只要其中的某个子线程完成了任务条件，就算任务完成，则调用 threadGroup.interrupt() 方法 其他的子线程就可以停止了

使用场景如

用户表按用户ID分成了10个表，这时候想通过用户昵称找到这个用户，则这时候就可以使用threadGroup中的 interrupt 来实现了

 package com.zyguo.thread;

 public class SearchRunnable implements Runnable{
     private int sleepTime;
     public SearchRunnable( int sleepTime ){
         this.sleepTime = sleepTime;
     }

     @Override
     public void run() {
         try {
             System.out.println( Thread.currentThread() + " begin search "  );
             Thread.sleep( sleepTime );
             System.out.println( Thread.currentThread() + " end search, 耗时 " + this.sleepTime );
         } catch (InterruptedException e) {
             System.out.println( Thread.currentThread() + " 被中断 "  );
             //e.printStackTrace();
         }
     }

 }

package com.zyguo.thread;

import java.util.ArrayList;

public class ThreadGroup_interrupt {
    public static void main(String[] args) {
        int threadNum = ;
        final ThreadGroup tgroup = new ThreadGroup("search-threadgroup");
        ArrayList<Thread> tList = new ArrayList<>();
        //定义10个线程
        for( int i = ; i < threadNum; i++ ){
            Thread t = new Thread( tgroup, new SearchRunnable(  + i*) ,"search-thread-" + i);
            tList.add( t );
            t.start();
            System.out.println("start thread = " + t );
        }

        //监控线程的活动的子线程数
        Thread t = new Thread( new Runnable() {
            @Override
            public void run() {
                int activeCount = tgroup.activeCount();
                while ( activeCount >  ) {
                    System.out.println("activeCount=" + activeCount );
                    if( activeCount <  ){
                        System.out.println("找到了需要的文件，开始终止其他的子线程"   );
                        tgroup.interrupt();
                        break;
                    }
                    try {
                        Thread.sleep();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    activeCount = tgroup.activeCount();
                }
            }
        });

        t.start();

    }
}

结果如下

start thread = Thread[search-thread-,,search-threadgroup]
Thread[search-thread-,,search-threadgroup] begin search
start thread = Thread[search-thread-,,search-threadgroup]
Thread[search-thread-,,search-threadgroup] begin search
start thread = Thread[search-thread-,,search-threadgroup]
Thread[search-thread-,,search-threadgroup] begin search
start thread = Thread[search-thread-,,search-threadgroup]
Thread[search-thread-,,search-threadgroup] begin search
start thread = Thread[search-thread-,,search-threadgroup]
Thread[search-thread-,,search-threadgroup] begin search
Thread[search-thread-,,search-threadgroup] begin search
start thread = Thread[search-thread-,,search-threadgroup]
start thread = Thread[search-thread-,,search-threadgroup]
Thread[search-thread-,,search-threadgroup] begin search
start thread = Thread[search-thread-,,search-threadgroup]
Thread[search-thread-,,search-threadgroup] begin search
start thread = Thread[search-thread-,,search-threadgroup]
Thread[search-thread-,,search-threadgroup] begin search
start thread = Thread[search-thread-,,search-threadgroup]
Thread[search-thread-,,search-threadgroup] begin search
activeCount=
activeCount=
activeCount=
activeCount=
activeCount=
Thread[search-thread-,,search-threadgroup] end search, 耗时
activeCount=
Thread[search-thread-,,search-threadgroup] end search, 耗时
activeCount=
Thread[search-thread-,,search-threadgroup] end search, 耗时
activeCount=
Thread[search-thread-,,search-threadgroup] end search, 耗时
activeCount=
Thread[search-thread-,,search-threadgroup] end search, 耗时
activeCount=
Thread[search-thread-,,search-threadgroup] end search, 耗时
activeCount=
找到了需要的文件，开始终止其他的子线程
Thread[search-thread-,,search-threadgroup] 被中断
Thread[search-thread-,,search-threadgroup] 被中断
Thread[search-thread-,,search-threadgroup] 被中断
Thread[search-thread-,,search-threadgroup] 被中断