SDSU CS 596: Client-Server Programming
Spring Semester, 1997
Doc 9, Threads part 2

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San Diego State University -- This page last updated Feb 25, 1997
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Contents of Doc 9, Threads part 2

    1. The End of an Application
    2. Ending Thread Execution
      1. The Preferred Way
      2. Stop
      3. destroy
    3. Debugging Threads
Doc 9, Threads part 2 Slide # 1

The End of an Application


When an program creates threads, what happens when the main ends before the other threads?
Types of Threads: user and daemon

A program ends when the last user thread is finished

All daemon threads running when the program ends are stopped

Doc 9, Threads part 2 Slide # 2
Daemon example 
class Test
   {
   public  static  void  main( String  args[] ) throws Exception{
      InfinityThread  shortLived      = new InfinityThread( );
      shortLived.setDaemon( true );
      shortLived.start();
      Thread.currentThread().sleep( 10 );
      System.out.println( "Bye");
      }
   }

class  InfinityThread  extends Thread
   {
   public  void run()
      {
      while (true)
         {
         System.out.println(  "From: " + getName()  );
         System.out.flush();
         yield();
         }
      }
   }
Output 
From: Thread-4
From: Thread-4
From: Thread-4
From: Thread-4
From: Thread-4
From: Thread-4
From: Thread-4
From: Thread-4
From: Thread-4
Bye


Doc 9, Threads part 2 Slide # 3

Ending Thread Execution


A thread ends when its run method returns
Forcing a Thread to Quit

The Preferred Way


Running thread checks to see if it is time to stop 
class Test {
   public  static  void  main( String  args[] ) throws Exception{
      NiceThread  missManners  = new NiceThread( );
      missManners.setPriority( 2 );
      missManners.start();
      Thread.currentThread().sleep( 5 );
      missManners.pleaseStop();
   }
}

class  NiceThread  extends Thread {
   protected boolean stopRequested = false;
   
   public void pleaseStop() { stopRequested = true; }

   public void run() {
      while (!stopRequested)
         System.out.println(  "From: " + getName()  );
      System.out.println( "The End" );
   }
}
Output 
From: Thread-2
From: Thread-2
From: Thread-2
From: Thread-2
From: Thread-2
The End


Doc 9, Threads part 2 Slide # 4
Forcing a Thread to Quit

Stop

class Test
   {
   public  static  void  main( String  args[] ) throws Exception
      {
      NotPoliteThread  outOfMyWay      = new NotPoliteThread( );
      outOfMyWay.setPriority( 2 );
      outOfMyWay.start();
      Thread.currentThread().sleep( 5 );
      outOfMyWay.stop();
      }
   }

class  NotPoliteThread  extends Thread
   {
   public void run()
      {
      while (1 < 2)
         {
         System.out.println(  "From: " + getName()  );
         System.out.flush();
         }
      System.out.println( "The End" );
      }
   }
Output 
From: Thread-2
From: Thread-2
From: Thread-2
From: Thread-2
From: Thread-2

Doc 9, Threads part 2 Slide # 5
Forcing a Thread to QuitThe Rambo Way

destroy


Do to the violent nature of destroy, no examples will be shown

Avoid using destroy, it does not allow any clean up to be done

Using destroy can leave other threads blocked forever

Doc 9, Threads part 2 Slide # 6

Debugging Threads


Some useful methods in Thread for debugging


public static void dumpStack()
Prints a stack trace for the current thread on System.out


public String toString()
Returns a String representation of the Thread, including the thread's name, priority and thread group.


public int countStackFrames()
Returns the number of stack frames in this Thread. The Thread must be suspended when this method is called.

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