Destroy Thread group

ThreadGroup class provides destroy method, to destroy a ThreadGroup, if the thread group empty. Empty mean, it don't have any active threads and all the sub groups also empty.

public final void destroy()

Destroys this thread group and all of its subgroups. This thread group must be empty, indicating that all threads that had been in this thread group have since stopped.

class GroupDestroyEx extends Thread{

 public void run(){
  try{
   Thread.currentThread().sleep(2000);
  }
  catch(Exception e){
  }
 }

 GroupDestroyEx(ThreadGroup grp, String name){
  super(grp, name);
 }

 public static void main(String args[])throws Exception{
  ThreadGroup group1 = new ThreadGroup("group1");
  ThreadGroup group2 = new ThreadGroup(group1, "group2");

  GroupDestroyEx thread1 = new GroupDestroyEx(group1, "thread1");
  GroupDestroyEx thread2 = new GroupDestroyEx(group1, "thread2");

  thread1.start();
  thread2.start();

  thread1.join();
  thread2.join();

  group1.destroy();
  System.out.println("Is group1 destroyed " + group1.isDestroyed());
  System.out.println("Is group1 destroyed " + group2.isDestroyed());
 }
}

   

Output

Is group1 destroyed true
Is group1 destroyed true

Some Points to Remember

1. IllegalThreadStateException thrown, when you tries to destroy a group, which has some active threads or active sub groups in it.

class GroupDestroyEx extends Thread{

 public void run(){
  try{
   Thread.currentThread().sleep(2000);
  }
  catch(Exception e){
  }
 }

 GroupDestroyEx(ThreadGroup grp, String name){
  super(grp, name);
 }

 public static void main(String args[])throws Exception{
  ThreadGroup group1 = new ThreadGroup("group1");
  ThreadGroup group2 = new ThreadGroup(group1, "group2");

  GroupDestroyEx thread1 = new GroupDestroyEx(group1, "thread1");
  GroupDestroyEx thread2 = new GroupDestroyEx(group1, "thread2");

  thread1.start();
  thread2.start();

  group1.destroy();

  System.out.println("Is group1 destroyed " + group1.isDestroyed());
  System.out.println("Is group1 destroyed " + group2.isDestroyed());
 }
}

   

Output

Exception in thread "main" java.lang.IllegalThreadStateException
  at java.lang.ThreadGroup.destroy(Unknown Source)
  at GroupDestroyEx.main(GroupDestroyEx.java:26)

   

Daemon Thread Group                                                 TimeUnit Class                                                 Home

Daemon Thread Group

public final void setDaemon(boolean daemon)

If the parameter daemon is set to true, then changes the daemon status of this thread group. A daemon thread group is automatically destroyed when its last thread is stopped or its last thread group is destroyed.

If the thread group is not daemon, then the group is not destroyed even when its last thread stopped. A daemon thread group can contain daemon and Non daemon threads in it.

Example

class DaemonGroupEx extends Thread{
 DaemonGroupEx(ThreadGroup grp, String name){
  super(grp, name);
 }

 public void run(){
  Thread local = Thread.currentThread();
  System.out.println(local.getName() + " is daemon " + local.isDaemon());
 }

 public static void main(String args[])throws Exception{
  ThreadGroup group1 = new ThreadGroup("group1");
  DaemonGroupEx t1 = new DaemonGroupEx(group1, "thread1");
  t1.start();
  t1.join();
  System.out.println("Is group1 destroyed " + group1.isDestroyed());
 }
}

Output

thread1 is daemon false
Is group1 destroyed false

A daemon thread group is automatically destroyed when its last thread is stopped or its last thread group is destroyed.

Example

class DaemonGroupEx extends Thread{
 DaemonGroupEx(ThreadGroup grp, String name){
  super(grp, name);
 }

 public void run(){
  Thread local = Thread.currentThread();
  System.out.println(local.getName() + " is daemon " + local.isDaemon());
 }

 public static void main(String args[])throws Exception{
  ThreadGroup group1 = new ThreadGroup("group1");
  group1.setDaemon(true);

  DaemonGroupEx t1 = new DaemonGroupEx(group1, "thread1");
  t1.start();
  t1.join();

  System.out.println("Is group1 destroyed " + group1.isDestroyed());
 }
}

Output  

thread1 is daemon false
Is group1 destroyed true

   

Related Posts

https://self-learning-java-tutorial.blogspot.com/2014/03/daemon-threads.html

Interrupt Thread Group                                                 Destroy Thread Group                                                 Home