/*
			     Condition Variables
				  Using DSS
				 Demo Program

				    CS509
				 Winter 1995
				 G. Lindstrom

*/

import sim.*;
import queues.*;
import random.*;

/*				   globals
*/

class cond_demo {

static int stop_time;				// simulation stop time
static urand interleave;			// simulates "truer" concurrency
static buffer buf;				// one globally declared buffer

public static void main(String av[])
{
  buf = new buffer(2, true);
  stop_time = 75;
  interleave = new urand(0, 2);

  scheduler.activate(new writer("writer 1", 100));
  scheduler.activate(new reader("reader A"));
  scheduler.activate(new writer("writer 2", 200));
  scheduler.activate(new reader("reader B"));
  scheduler.activate(new writer("writer 3", 300));
  scheduler.activate(new reader("reader C"));
  scheduler.activate(new writer("writer 4", 400));
  scheduler.activate(new reader("reader D"));

  scheduler.run_simulation();
}

}
/*			      class declarations
*/

/* buff_elem not needed */

/*			   buffer member functions
*/
class buffer extends Queue {		// buffer class; hide inherited get/put
  int size;				// maximum number of elements
  boolean verbose;				// show trace?
  resource  mutex;			// mutex guarding this buffer
  condition_var not_empty;		// writers signal readers
  condition_var not_full;		// readers signal writers

  buffer(int s, boolean v)
  {
    size = s; verbose = v;
    mutex = new resource("buffer mutex");
    not_empty = new condition_var("buffer not empty", verbose);
    not_full = new condition_var("buffer not full", verbose);
  }

  public void Enqueue(Object o)		// redefined for "interleaving"
  {
      scheduler.hold(cond_demo.interleave.draw());

      mutex.request();

      while (Length() == size) {    // current process holds mutex
	scheduler.hold(cond_demo.interleave.draw());

	not_full.wait(mutex);	// mutex temporarily released within wait

	// current process again holds mutex
      }

      // buffer not full now; current process has lock
      scheduler.hold(cond_demo.interleave.draw());

      super.Enqueue(o);		// safely do put
      scheduler.hold(cond_demo.interleave.draw());

      not_empty.signal();		// signal a waiting reader (if any)
      scheduler.hold(cond_demo.interleave.draw());

      mutex.release();
  }

  public Object Dequeue()		// redefined for "interleaving"
  {
      Object result;
      scheduler.hold(cond_demo.interleave.draw());

      mutex.request();

      while (Length() == 0) {    // current process holds mutex
	scheduler.hold(cond_demo.interleave.draw());

	not_empty.wait(mutex);	// mutex temporarily released within wait

	// current process again holds mutex
      }

      // buffer not empty now; current process has lock
      scheduler.hold(cond_demo.interleave.draw());

      result = super.Dequeue();	// safely do get
      scheduler.hold(cond_demo.interleave.draw());

      not_full.signal();		// signal a waiting writer (if any)
      scheduler.hold(cond_demo.interleave.draw());

      mutex.release();
      return result;
  }
};

/*			   writer member functions
*/

class writer extends process 
{
    int base;

writer(String n, int b)
{
  super(n);
  base = b;
}

void body() {
  while ( scheduler.clock < cond_demo.stop_time ) {
    scheduler.hold(cond_demo.interleave.draw());

    base++;
    System.out.println("Time " + scheduler.clock + ": " + 
	name + " initiates write of " + base);

			// all concurrency control hidden
    cond_demo.buf.Enqueue(new Integer(base));	

    System.out.println("Time " + scheduler.clock + ": " + 
	name + " completes write of " + base);
  }  
}

}

/*			   reader member functions
*/

class reader extends process
{

reader(String n)
{
    super(n);
}

void body() {
  Integer be;
  while ( scheduler.clock < cond_demo.stop_time ) {
    scheduler.hold(cond_demo.interleave.draw());

    System.out.println("Time " + scheduler.clock + ": " + 
	name + " initiates read");
			// all concurrency control hidden
    be = (Integer)cond_demo.buf.Dequeue();	

    System.out.println("Time " + scheduler.clock + ": " + 
	name + " completes read of " + be);

  }
}

}