gistfile1.txt

import java.util.concurrent.Semaphore;


public class Sem1 implements Runnable
{
   private int num;
   private static Semaphore sem = new Semaphore( 0, true );


   Sem1( int num ) 
   {
      this.num = num;
   }

   public void run() {
      System.out.println( "Thread " + num + " waiting" );
      try
      {
         sem.acquire();
      }
      catch (InterruptedException e)
      {
      }
      System.out.println( "Thread " + num + " resuming" );
   }

   public static void post()
   {
      sem.release();
   }

   public static void main(String args[])
   {
      int i=0;
      final int NUMTHREADS = 10;

      Sem1 thr[] = new Sem1[NUMTHREADS];
      Thread myThread[] = new Thread[NUMTHREADS];

      // create threads
      for( i = 0; i < NUMTHREADS; ++i ) 
      {
         thr[i] = new Sem1(i);
         myThread[i] = new Thread( thr[i] );
         myThread[i].start();
      }

      try
      {
         Thread.sleep(2000);
      }
      catch (InterruptedException e)
      {
      }

      // awaken threads
      for( i = 0; i < NUMTHREADS; ++i )  {
	      System.out.println("Posting from main");
         post(); 
      }

      for( i = 0; i < NUMTHREADS; ++i )  {
	     try   {
	        myThread[i].join();
	     }
	     catch (InterruptedException e) {
	     }
      }
   }
}