Java并发编程之ThreadGroup

ThreadGroup是Java提供的一种对线程进行分组管理的手段，可以对所有线程以组为单位进行操作，如设置优先级、守护线程等。

线程组也有父子的概念，如下图：

线程组的创建

 public class ThreadGroupCreator {

     public static void main(String[] args) {
         //获取当前线程的group
         ThreadGroup currentGroup = Thread.currentThread().getThreadGroup();
         //在当前线程执行流中新建一个Group1
         ThreadGroup group1 = new ThreadGroup("Group1");
         //Group1的父线程,就是main线程所在Group
         System.out.println(group1.getParent() == currentGroup);
         //定义Group2, 指定group1为其父线程
         ThreadGroup group2 = new ThreadGroup(group1, "Group2");
         System.out.println(group2.getParent() == group1);
     }
 }

线程组的基本操作

注意：后添加进线程组的线程，其优先级不能大于线程组的优先级

 public class ThreadGroupBasic {

     public static void main(String[] args) throws InterruptedException {

         ThreadGroup group = new ThreadGroup("group1");
         Thread thread = new Thread(group, () -> {
             while(true) {
                 try {
                     TimeUnit.SECONDS.sleep(1);
                 } catch (InterruptedException e) {
                     e.printStackTrace();
                 }
             }
         }, "thread");
         thread.setDaemon(true);
         thread.start();

         TimeUnit.MILLISECONDS.sleep(1);

         ThreadGroup mainGroup = Thread.currentThread().getThreadGroup();
         //递归获取mainGroup中活跃线程的估计值
         System.out.println("activeCount = " + mainGroup.activeCount());
         //递归获mainGroup中的活跃子group
         System.out.println("activeGroupCount = " + mainGroup.activeGroupCount());
         //获取group的优先级, 默认为10
         System.out.println("getMaxPriority = " + mainGroup.getMaxPriority());
         //获取group的名字
         System.out.println("getName = " + mainGroup.getName());
         //获取group的父group, 如不存在则返回null
         System.out.println("getParent = " + mainGroup.getParent());
         //活跃线程信息全部输出到控制台
         mainGroup.list();
         System.out.println("----------------------------");
         //判断当前group是不是给定group的父线程, 如果两者一样,也会返回true
         System.out.println("parentOf = " + mainGroup.parentOf(group));
         System.out.println("parentOf = " + mainGroup.parentOf(mainGroup));

     }

 }

线程组的Interrupt

 ublic class ThreadGroupInterrupt {

     public static void main(String[] args) throws InterruptedException {
         ThreadGroup group = new ThreadGroup("TestGroup");
         new Thread(group, () -> {
             while(true) {
                 try {
                     TimeUnit.MILLISECONDS.sleep(2);
                 } catch (InterruptedException e) {
                     //received interrupt signal and clear quickly
                     System.out.println(Thread.currentThread().isInterrupted());
                     break;
                 }
             }
             System.out.println("t1 will exit");
         }, "t1").start();
         new Thread(group, () -> {
             while(true) {
                 try {
                     TimeUnit.MILLISECONDS.sleep(2);
                 } catch (InterruptedException e) {
                     //received interrupt signal and clear quickly
                     System.out.println(Thread.currentThread().isInterrupted());
                     break;
                 }
             }
             System.out.println("t2 will exit");
         }, "t2").start();
         //make sure all threads start
         TimeUnit.MILLISECONDS.sleep(2);

         group.interrupt();
     }

 }

线程组的destroy

 public class ThreadGroupDestroy {

     public static void main(String[] args) {
         ThreadGroup group = new ThreadGroup("TestGroup");
         ThreadGroup mainGroup = Thread.currentThread().getThreadGroup();
         //before destroy
         System.out.println("group.isDestroyed=" + group.isDestroyed());
         mainGroup.list();

         group.destroy();
         //after destroy
         System.out.println("group.isDestroyed=" + group.isDestroyed());
         mainGroup.list();
     }

 }

线程组设置守护线程组

线程组设置为守护线程组，并不会影响其线程是否为守护线程，仅仅表示当它内部没有active的线程的时候，会自动destroy

 public class ThreadGroupDaemon {

     public static void main(String[] args) throws InterruptedException {
         ThreadGroup group1 = new ThreadGroup("group1");
         new Thread(group1, () -> {
             try {
                 TimeUnit.SECONDS.sleep(1);
             } catch (InterruptedException e) {
                 e.printStackTrace();
             }
         }, "group1-thread1").start();
         ThreadGroup group2 = new ThreadGroup("group2");
         new Thread(group2, () -> {
             try {
                 TimeUnit.SECONDS.sleep(1);
             } catch (InterruptedException e) {
                 e.printStackTrace();
             }
         }, "group1-thread2").start();
         group2.setDaemon(true);

         TimeUnit.SECONDS.sleep(3);
         System.out.println(group1.isDestroyed());
         System.out.println(group2.isDestroyed());
     }
 }