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());
}
}