// A handshake implemented using general semaphores.
//
// SGM 28/10/99

class handshake1 {

   private Object local ;
   semaphore2 semin = new semaphore2(0) ;
   semaphore2 semout = new semaphore2(0) ;

   public void send(Object x) {
     local = x ;               // Write message.
     semin.V() ;               // Signal that message is now written.
     semout.P() ;              // Wait here until message has been read.
   }

   public Object receive() {
     semin.P() ;               // Wait here until message has been written.
     semout.V() ;              // Signal that message has been read.
     return(local) ;           // Read message.  (Note : Java insists that the
                               // `return' must be the last statement in a 
                               // returning method, which is why the last two
                               // statements appear to be the wrong way round.)
   }
}