/**
 * <p>This program demonstrates the use of Java monitor through
 * the "synchronized" method.</p>
 *
 * <p>When tring out the program, if the "synchronized" keyword
 * is commented out in the Counter.increment() method, then
 * the Counter object is not protected by the monitor, the resulting
 * value of the counter will be incorrect, especially with large
 * number of threads (e.g., 500).</p>
 *
 * <p>For CSCI 315 class demonstration.</p>
 * 
 * @author Xiannong Meng
 * @date 09-27-2013
 */
public class CounterDemo  extends Thread {

    public static final int SIZE = 50;
    public static int finishCount = 0;

    /* The test program */
    public static void main(String [] args)  {

	CounterDemo demo = new CounterDemo();
	demo.runDemo();
    }

    public void runDemo() {

	Counter b = new Counter(0);    // Shared counter among threads

	Worker w[] = new Worker[SIZE]; // create an array of threads
	for (int i = 0; i < SIZE; i ++)
	    w[i] = new Worker(b, i);   // create each Worker()

	for (int i = 0; i < SIZE; i ++)
	    w[i].start();              // start each thread

	// busy waiting for all threads to finish, 
	// didn't find a better and easier mechanism
	// should be improved
	while (finishCount < SIZE) {   
	    try {
		Thread.sleep(10);
	    } catch (InterruptedException e) {}
	}
	System.out.println("value after " + b.get());
    }
}

class Worker extends Thread {

    private Counter value;
    private int id;
     
    Worker(Counter b, int id) { value = b; this.id = id;}

    public void run() {
	for(int i = 0; i < 10; i++) {
	    this.value.increment();
	}

	CounterDemo.finishCount ++;
	//     System.out.println("value " + this.value.get() + " in thread " + this.id);
    }
}    


class Counter {

    private int count;
    Counter(int init) { this.count = init; }
    
    /*
     * Toggle between "synchronized" or not one would test
     * the effects of the monitor.
     * Without "synchronized" the result will be incorrect.
     */
    public synchronized void increment() {
	//    public void increment() {
	this.count ++;
    }

    public int get() {
	return this.count;
    }
}