Suspend Resume Thread Java

Introduction to Suspend Resume Thread

When the sleep() method time is over, the thread becomes implicitly active. sleep() method is preferable when the inactive time is known earlier. Sometimes, the inactive time or blocked time may not be known to the programmer earlier; to come to the task here comes suspend() method. The suspended thread will be in blocked state until resume() method is called on it. These methods are deprecated, as when not used with precautions, the thread locks, if held, are kept in inconsistent state or may lead to deadlocks.

Note: You must have noticed, in the earlier sleep() method, that the thread in blocked state retains all its state. That is, attribute values remains unchanged by the time it comes into runnable state.

Suspend Resume Thread: Program explaining the usage of suspend() and resume() methods

public class SRDemo extends Thread   
{
 public static void main( String args[ ] )   
 {
   SRDemo srd1 = new SRDemo();   
   SRDemo srd2 = new SRDemo();   
   srd1.setName("First");
   srd2.setName("Second");
   srd1.start();      
   srd2.start();
   try   
   {
     Thread.sleep( 1000 );
     srd1.suspend();
     System.out.println("Suspending thread First");
     Thread.sleep( 1000 );
     srd1.resume();
     System.out.println("Resuming thread First");

     Thread.sleep(1000);
     srd2.suspend();
     System.out.println("Suspending thread Second");
     Thread.sleep(1000);
     srd2.resume();
     System.out.println("Resuming thread Second");
   }
   catch(InterruptedException e)   
   {  
     e.printStackTrace();   
   }
 }
 public void run()   
 {                  		
  try  
  {
   for(int i=0; i<7; i++)   
   {
     Thread.sleep(500);
     System.out.println( this.getName() + ":  " + i );
   }
  }
  catch(InterruptedException e)   
  { 
    e.printStackTrace();  
  }
 }
}  

Output screen on Suspend Resume Thread Java

Observe the screenshot, when no thread is suspended both threads are under execution. When First thread goes into suspended state, the Second thread goes into action. Similarly, when the Second goes to suspended state, the First is executed.

Note: When you compile this program, you will get deprecated warning. But the program works happily.

Note: Depending on the microprocessor speed and OS architecture, you may get a different output or different outputs at different times of execution. But do not worry.