public class Counter {
  int value = 0;

  // Non-atomic increment of value
  void increment() {
    int temp = value;     //read value
    HWinterrupt();
    value = temp + 1;     //write value
  }

  // Sometimes an interrupt happens and another thread is
  // scheduled to run
  void HWinterrupt() {
    try {
      if (Math.random()>0.80)
	Thread.sleep((int)(Math.random()*500));
    } catch(InterruptedException e ) {e.printStackTrace();}
  }
  
  int getValue() {
    return value;
  }

  public static void main(String args[]){
    Counter test = new Counter();
    Trd t1 = new Trd(test);
    Trd t2 = new Trd(test);

    t1.start();
    t2.start();

    // Wait for the Threads to finish
    try {
      t1.join();
      t2.join();
    } catch(InterruptedException e ) {e.printStackTrace();}
    
    System.out.println( "Value should be: 40, but is: " + test.getValue() );
  }
}

class Trd extends Thread {
  Counter counter;

  public Trd(Counter c) {
    counter = c;
  }

  // Call increment on the counter 20 times
  public void run() {
    for (int i = 0; i < 20; i++) {
      counter.increment();
    }
  }
}