Main thread in Java

Software Development
#1

Hello Everyone,

Java provides built-in support for multithreaded programming. A multi-threaded program contains two or more parts that can run concurrently. Each part of such a program is called a thread, and each thread defines a separate path of execution.

Main Thread

When a Java program starts up, one thread begins running immediately. This is usually called the main thread of our program, because it is the one that is executed when our program begins.

Properties :

  • It is the thread from which other “child” threads will be spawned.
  • Often, it must be the last thread to finish execution because it performs various shutdown actions

How to control Main thread

The main thread is created automatically when our program is started. To control it we must obtain a reference to it. This can be done by calling the method currentThread( ) which is present in Thread class. This method returns a reference to the thread on which it is called. The default priority of Main thread is 5 and for all remaining user threads priority will be inherited from parent to child.

// Java program to control the Main Thread

public class Test extends Thread

{

public static void main(String[] args)

{

// getting reference to Main thread

Thread t = Thread.currentThread();

// getting name of Main thread

System.out.println( "Current thread: " + t.getName());

// changing the name of Main thread

t.setName( "Geeks" );

System.out.println( "After name change: " + t.getName());

// getting priority of Main thread

System.out.println( "Main thread priority: " + t.getPriority());

// setting priority of Main thread to MAX(10)

t.setPriority(MAX_PRIORITY);

System.out.println( "Main thread new priority: " + t.getPriority());

for ( int i = 0 ; i < 5 ; i++)

{

System.out.println( "Main thread" );

}

// Main thread creating a child thread

ChildThread ct = new ChildThread();

// getting priority of child thread

// which will be inherited from Main thread

// as it is created by Main thread

System.out.println( "Child thread priority: " + ct.getPriority());

// setting priority of Main thread to MIN(1)

ct.setPriority(MIN_PRIORITY);

System.out.println( "Child thread new priority: " + ct.getPriority());

// starting child thread

ct.start();

}

}

// Child Thread class

class ChildThread extends Thread

{

@Override

public void run()

{

for ( int i = 0 ; i < 5 ; i++)

{

System.out.println( "Child thread" );

}

}

}

Output:

Current thread: main After name change: Geeks Main thread priority: 5 Main thread new priority: 10 Main thread Main thread Main thread Main thread Main thread Child thread priority: 10 Child thread new priority: 1 Child thread Child thread Child thread Child thread Child thread

Deadlocking with use of Main Thread(only single thread)

We can create a deadlock by just using Main thread, i.e. by just using a single thread. The following java program demonstrate this.

// Java program to demonstrate deadlock

// using Main thread

public class Test

{

public static void main(String[] args)

{

try

{

System.out.println( "Entering into Deadlock" );

Thread.currentThread().join();

// the following statement will never execute

System.out.println( "This statement will never execute" );

}

catch (InterruptedException e)

{

e.printStackTrace();

}

}

}

Output:

Entering into Deadlock

Explanation :
The statement “Thread.currentThread().join()”, will tell Main thread to wait for this thread(i.e. wait for itself) to die. Thus Main thread wait for itself to die, which is nothing but a deadlock.