Examples and methods of using thread groups in Java

Thread group in Java (ThreadGroup class)

The ThreadGroup class is used in Java to represent a thread group, which represents a collection of threads and can manage a batch of threads and thread groups. Threads can be assigned to a certain thread group. There can be thread objects in the thread group, there can also be thread groups, and there can also be threads in the group. This organizational structure is somewhat similar to the form of a tree, as shown in the figure.

All threads created by the user belong to the specified thread group. If no thread group is explicitly specified, the thread belongs to the default thread group (ie, main thread group). By default, the child thread and the parent thread are in the same thread group.

In addition, the thread group to which a thread belongs can only be specified when the thread is created. The thread group to which it belongs cannot be changed while the thread is running. That is to say, the thread group to which a thread belongs cannot be changed once it is specified.

2. Why use thread groups

1.Safety

Threads in the same thread group can modify each other's data. But if they are in different thread groups, then the data cannot be modified "cross-thread groups", and data security can be guaranteed to a certain extent.

2. Batch management

Threads or thread group objects can be managed in batches to effectively organize or control threads or thread group objects.

3. Thread group usage example

1. Thread association thread group: first-level association

The so-called first-level association means that the parent object has child objects, but no grandchild objects are created. For example, create a thread group, and then assign the created threads to the group to effectively manage these threads. The code example is as follows:

public class ThreadGroupTest {
 public static void main(String[] args) {
 ThreadGroup rootThreadGroup = new ThreadGroup("root线程组");
 Thread thread0 = new Thread(rootThreadGroup, new MRunnable(), "线程A");
 Thread thread1 = new Thread(rootThreadGroup, new MRunnable(), "线程B");
 thread0.start();
 thread1.start();
 }
}
class MRunnable implements Runnable {
 @Override
 public void run() {
 while (!Thread.currentThread().isInterrupted()) {
 System.out.println("线程名: " + Thread.currentThread().getName() 
+ ", 所在线程组: " + Thread.currentThread().getThreadGroup().getName()) ;
 try {
 Thread.sleep(1000);
 } catch (InterruptedException e) {
 e.printStackTrace();
 }
 }
 }
}
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The execution results are as follows:

线程名: 线程A, 所在线程组: root线程组
线程名: 线程B, 所在线程组: root线程组
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2. Thread association thread group: multi-level association

The so-called multi-level association means that the parent object has child objects, and creating a grandchild object in the child object will have the effect of descendants. For example, use the second construction method in the figure below to attribute the sub-thread group to a certain thread group, and then attribute the created thread to the sub-thread group. This will have the effect of a thread tree.

The code example is as follows:

public class ThreadGroupTest {
 public static void main(String[] args) {
 ThreadGroup rootThreadGroup = new ThreadGroup("root线程组");
 Thread thread0 = new Thread(rootThreadGroup, new MRunnable(), "线程A");
 Thread thread1 = new Thread(rootThreadGroup, new MRunnable(), "线程B");
 thread0.start();
 thread1.start();
 ThreadGroup threadGroup1 = new ThreadGroup(rootThreadGroup, "子线程组");
 Thread thread2 = new Thread(threadGroup1, new MRunnable(), "线程C");
 Thread thread3 = new Thread(threadGroup1, new MRunnable(), "线程D");
 thread2.start();
 thread3.start();
 }
}
class MRunnable implements Runnable {
 @Override
 public void run() {
 while (!Thread.currentThread().isInterrupted()) {
 System.out.println("线程名: " + Thread.currentThread().getName()
 + ", 所在线程组: " + Thread.currentThread().getThreadGroup().getName()
 + ", 父线程组: " + Thread.currentThread().getThreadGroup().getParent().getName());
 try {
 Thread.sleep(1000);
 } catch (InterruptedException e) {
 e.printStackTrace();
 }
 }
 }
}
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The execution results are as follows:

线程名: 线程A, 所在线程组: root线程组, 父线程组: main
线程名: 线程B, 所在线程组: root线程组, 父线程组: main
线程名: 线程C, 所在线程组: 子线程组, 父线程组: root线程组
线程名: 线程D, 所在线程组: 子线程组, 父线程组: root线程组
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3. Batch management of threads in the group

Naturally, using a thread group requires batch management of threads. For example, you can batch interrupt threads in the group. The code example is as follows:

public class ThreadGroupTest {
 public static void main(String[] args) {
 ThreadGroup rootThreadGroup = new ThreadGroup("root线程组");
 Thread thread0 = new Thread(rootThreadGroup, new MRunnable(), "线程A");
 Thread thread1 = new Thread(rootThreadGroup, new MRunnable(), "线程B");
 thread0.start();
 thread1.start();
 ThreadGroup threadGroup1 = new ThreadGroup(rootThreadGroup, "子线程组");
 Thread thread2 = new Thread(threadGroup1, new MRunnable(), "线程C");
 Thread thread3 = new Thread(threadGroup1, new MRunnable(), "线程D");
 thread2.start();
 thread3.start();
 rootThreadGroup.interrupt();
 System.out.println("批量中断组内线程");
 }
}
class MRunnable implements Runnable {
 @Override
 public void run() {
 while (!Thread.currentThread().isInterrupted()) {
 System.out.println("线程名: " + Thread.currentThread().getName()
 + ", 所在线程组: " + Thread.currentThread().getThreadGroup().getName()
 + ", 父线程组: " + Thread.currentThread().getThreadGroup().getParent().getName());
 try {
 Thread.sleep(1000);
 } catch (InterruptedException e) {
 e.printStackTrace();
 break;
 }
 }
 System.out.println(Thread.currentThread().getName() + "执行结束");
 }
}
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The execution result is as follows:

线程名: 线程A, 所在线程组: root线程组, 父线程组: main
线程名: 线程B, 所在线程组: root线程组, 父线程组: main
线程名: 线程C, 所在线程组: 子线程组, 父线程组: root线程组
线程名: 线程D, 所在线程组: 子线程组, 父线程组: root线程组
批量中断组内线程
线程A执行结束
线程B执行结束
线程C执行结束
线程D执行结束
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