/**
  * Copyright (c): Uwe Schmidt, FH Wedel
  *
  * You may study, modify and distribute this source code
  * FOR NON-COMMERCIAL PURPOSES ONLY.
  * This copyright message has to remain unchanged.
  *
  * Note that this document is provided 'as is',
  * WITHOUT WARRANTY of any kind either expressed or implied.
  */

/** a Test for synchronised
  * access of a buffer with 2 variables
  * and sequential producer consumer access
  */

//----------------

class Resource {

  // the empty/full flag
  public
  boolean empty = true;

  public
  int i,j;

  public
  Resource() {
    i = 0;
    j = 0;
  }
}

//----------------

public
class SyncTest {

  // the shared global resource buffer
  // used by both threads
  // both buffer variables i and j
  // always contain the same value

  public static
  Resource buffer = new Resource();

  //----------------

  // the main method
  public static
  void main(String[] argv) {
    Thread producer =
      new Producer(buffer);

    Thread consumer =
      new Consumer(buffer);

    producer.setName("producer");
    consumer.setName("consumer");

    producer.start();
    consumer.start();
  }
}

//----------------

abstract
class SleepyThread extends Thread {

  public
  void sleepAWhile() {
    try {
      sleep( (int)(Math.random() * 500) );
    }
    catch ( InterruptedException e ) { }
  }

  //----------------

  public
  abstract
  void doIt();

  //----------------

  public
  void run() {
    System.out.println(getName() + " started");

    for (int i = 0;
	 i < 10;
	 ++ i ) {
      doIt();
      sleepAWhile();
    }

    System.out.println(getName() + " finished");
  }
}

//----------------

class Producer extends SleepyThread {

  // the shared buffer
  private
  Resource buffer;

  public Producer(Resource buffer) {
    super();
    this.buffer = buffer;
  }

  //----------------

  public
  void doIt() {
    synchronized ( buffer ) {

      while ( ! buffer.empty ) {
	// producer must wait until buffer empty
	try {
	  System.out.println(getName() + " waiting");
	  buffer.wait();
	}
	catch ( InterruptedException e ) { }
	System.out.println(getName() + " notified");
      }

      System.out.println(getName() + " incrementing i");
      // modify 1. variable
      ++ buffer.i;

      // simulate some complex computations
      sleepAWhile();

      System.out.println(getName() + " incrementing j");
      // modify 2. variable
      ++ buffer.j;

      buffer.empty = false;

      buffer.notify();
    }
  }
}

//----------------

class Consumer extends SleepyThread {

  // the shared buffer
  private
  Resource buffer;

  public Consumer(Resource buffer) {
    super();
    this.buffer = buffer;
  }

  //----------------

  public
  void doIt() {
    synchronized ( buffer ) {
      int i,j;

      while ( buffer.empty ) {
	// consumer must wait until buffer is full
	try {
	  System.out.println(getName() + " waiting");
	  buffer.wait();
	}
	catch ( InterruptedException e ) { }
	System.out.println(getName() + " notified");
      }

      System.out.println(getName() + " reading i");
      // read 1. variable
      i = buffer.i;

      // simulate some complex computations
      sleepAWhile();

      System.out.println(getName() + " reading j");
      // reading 2. variable
      j = buffer.j;

      System.out.println(getName() + " i,j = " + i + "," + j);

      buffer.empty = true;

      buffer.notify();
    }
  }
}