// Unrolled and not inlined version with 2 readers and 2 writers
// No data structure used for readers and writers to work with
// Specific notification locks are used to improve performance

class RWnotif {
  static Controller ctl;

  public static void main (String argv[]) {
    ctl = new Controller();

      new Reader1(ctl).start();
      new Reader2(ctl).start();
      new Writer1(ctl).start();
      new Writer2(ctl).start();
  }
}


final class Reader1 extends Thread {
  protected Controller ctl;

  public Reader1(Controller c) { ctl = c;}

  public void run()
  {
    while (true) {
      ctl.startRead();
      System.out.println("reader reading:");
      System.out.println("done reading");
      ctl.stopRead();
    }

  } // end public void run()
}
final class Reader2 extends Thread {
  protected Controller ctl;

  public Reader2(Controller c) { ctl = c;}

  public void run()
  {
    while (true) {
      ctl.startRead();
      System.out.println("reader reading:");
      System.out.println("done reading");
      ctl.stopRead();
    }
  } // end public void run()
}

final class Writer1 extends Thread {
  protected Controller ctl;

  public Writer1(Controller c) { ctl = c;}  

  public void run()  
  {  
    while (true) {
      ctl.startWrite();
      System.out.println("writer writing:");
      System.out.println("done writing");
      ctl.stopWrite();
    }
  } // end public void run()
}

final class Writer2 extends Thread {
  protected Controller ctl;
    
  public Writer2(Controller c) { ctl = c;}

  public void run()
  {
    while (true) {
      ctl.startWrite();
      System.out.println("writer writing:");
      System.out.println("done writing");
      ctl.stopWrite();
    }
  } // end public void run()
}


class Controller
{
    private int nr = 0;
    private int nw = 0;
    private Object or = new Object();
    private Object ow =  new Object();
   
    public void startRead()
    {
	synchronized(or)
	{
	    while(!checkRead())
		try{or.wait();
		   }catch(InterruptedException e){}
	}
    }

    private synchronized boolean checkRead()
    {
	if(nw == 0)
	{
	    nr++;
	    return true;
      	}
	else return false;
    }

    public void stopRead()
    {
	synchronized(this){nr--;}
	synchronized(ow){ow.notify();}
    }

    public void startWrite()
    {
	synchronized(ow)
	{
	    while(!checkWrite())
		try{ow.wait();
		   }catch(InterruptedException e) {}
	}
    }

    private synchronized boolean checkWrite()
    {
	if((nw == 0) && (nr == 0))
	{
	    nw++;
	    return true;
	}
	else return false;
    }

    public void stopWrite()
    {
	synchronized(this){nw--;}
	synchronized(or){or.notifyAll();}
	synchronized(ow){ow.notify();}
    }
}