/*
Taken from "The Art of Multiprocessor Programming" by Herlihy, Maurice and Shavit, Nir and slightly modified.
*/
import java.util.concurrent.locks.ReentrantLock ;

public class CounterLock {
  private int value ;
  private ReentrantLock mutex = new ReentrantLock() ;             // to protect critical section

  public CounterLock (int c) {    // constructor
    value = c ;
  }

  // get method for the value
  public int getValue() {
    return value;
  }

  // increment and return prior value
  public int getAndIncrement() {
    mutex.lock() ;             // enter critical section
    int temp = 0 ;
    try {
      // start of critical section
      temp = value ;         
      System.out.println("temp: " + temp);
      value = temp + 1 ;      
      // end of critical section
    } finally {
      mutex.unlock() ;         // exit critical section
    }
    return temp ;
  }

 
  public static void main (String args[]) throws InterruptedException {
    Thread[] thread = new Thread[200] ;
    CounterLock counter = new CounterLock(0) ;    // shared by all threads

    // create threads
    for (int i = 0; i < thread.length; i++) {
      thread[i] = new Thread(new Runnable() {
        public void run() {
          int n = counter.getAndIncrement();
        }
      }) ;
    }

    // start threads
    for (int i = 0; i < thread.length; i++) {
      thread[i].start() ;
    }

    // wait for threads to finish
    for (int i = 0; i < thread.length; i++) {
      thread[i].join();
    }

    System.out.println("final value of counter: "+ counter.getValue());
  }
}