Thread Groups

In this article we will learn what is a thread group? How to work with thread groups in Java along with example program.

A thread group is a collection of threads. A thread group allows the programmer to maintain a group of threads more effectively. To support thread groups Java provides a class named ThreadGroup available in java.lang package.

Some of the constructors available in ThreadGroup class are:

ThreadGroup(String group-name)

ThreadGroup(ThreadGroup parent, String group-name)

After creating a thread group using one of the above constructors, we can add a thread to the thread group using one of the following Thread constructors:

Thread(ThreadGroup ref, Runnable obj)

Thread(ThreadGroup ref, String thread-name)

Thread(ThreadGroup ref, Runnable obj, String thread-name)

Following are some of the methods available in ThreadGroup class:

• getName() – To get the name of the thread group
• setMaxPriority() – To set the maximum priority of all the threads in the group
• setMinPriority() – To set the minimum priority of all the threads in the group
• start() – To start the execution of all the threads in the group
• list() – To print information of the thread group and the threads in the group.

Below program demonstrates the use of thread groups in Java:

class ChildThread implements Runnable
{
	Thread t;
	ChildThread(ThreadGroup g, String name)
	{
		t = new Thread(g,this,name);
		g.setMaxPriority(8);
		System.out.println(t.getName()+" belongs to the group: "+g.getName());
		System.out.println("Maximum priority of "+g.getName()+" is: "+g.getMaxPriority());
		t.start();
	}
	public void run()
	{
		try
		{
			for(int i=1;i<=10;i++)
			{
				System.out.println(t.getName()+":"+i);
				Thread.sleep(1000);
			}
		}
		catch(InterruptedException e)
		{
			System.out.println(t.getName()+" is interrupted");
		}
	}
}

public class Driver
{	
	public static void main(String[] args) throws InterruptedException
	{
		ThreadGroup tg1 = new ThreadGroup("Group A");
		ChildThread one = new ChildThread(tg1, "First Thread");
		ChildThread two = new ChildThread(tg1, "Second Thread");
		try
		{
			Thread.sleep(3000);
			System.out.println("All the threads in the group will be stopped");
			tg1.stop();
		}
		catch(InterruptedException e)
		{
			System.out.println("main thread is interrupted");
		}
		tg1.list();		
	}
}

Output of the above program is:

First Thread belongs to the group: Group A
Maximum priority of Group A is: 8
Second Thread belongs to the group: Group A
Maximum priority of Group A is: 8
First Thread:1
Second Thread:1
First Thread:2
Second Thread:2
Second Thread:3
First Thread:3
All the threads in the group will be stopped
java.lang.ThreadGroup[name=Group A,maxpri=8]
Thread[First Thread,5,Group A]
Thread[Second Thread,5,Group A]

Suryateja Pericherla

Suryateja Pericherla, at present is a Research Scholar (full-time Ph.D.) in the Dept. of Computer Science & Systems Engineering at Andhra University, Visakhapatnam. Previously worked as an Associate Professor in the Dept. of CSE at Vishnu Institute of Technology, India.

He has 11+ years of teaching experience and is an individual researcher whose research interests are Cloud Computing, Internet of Things, Computer Security, Network Security and Blockchain.

He is a member of professional societies like IEEE, ACM, CSI and ISCA. He published several research papers which are indexed by SCIE, WoS, Scopus, Springer and others.