// Unrolled and not inlined version with 2 readers and 2 writers
// No data structure used for readers and writers to work with
// No priorities given or policies used in this example

class RWempty {
  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()
}

final class Controller {
  protected int activeReaders = 0;  
  protected boolean writerPresent = false;  

  protected boolean writeCondition() {
    return activeReaders == 0 && !writerPresent;
  }

  protected boolean readCondition() {
    return !writerPresent;
  }

  protected synchronized void startRead() {
    while (!readCondition())
      try { wait(); } catch (InterruptedException ex) {}
    ++activeReaders;
  }

  protected synchronized void stopRead()  { 
    --activeReaders;
    notifyAll();
  }

  protected synchronized void startWrite() {
    while (!writeCondition()) 
      try { wait(); } catch (InterruptedException ex) {}
    writerPresent = true;
  }

  protected synchronized void stopWrite() { 
    writerPresent = false;
    notifyAll();
  }
}