/*
 * SynchRácer.java
 *
 * 1.0
 *
 * 000908
 *
 * Leif Lindbäck.
 *
 */


/**
 * A runnable used to cause a race condition.
 */
public class SynchRacer implements Runnable {
    private UpdateMe um;
    private final int NO_OF_UPDATES = 200000;
    
    /**
     * Constructs a SynchRacer that will update the specified UpdateMe object.
     */
    public SynchRacer( UpdateMe um ) {
	this.um = um;
    }
    
    /**
     * Updates um NO_OF_UPDATES times and print the result.
     */
    public void run() {
	
	System.out.println( Thread.currentThread() + " starting");
	for (int i = NO_OF_UPDATES; i>0; i--) {
	    um.addToValue( 10 );
	}
	for (int i = NO_OF_UPDATES; i>0; i--) {
	    um.addToValue( -10 );
	}
	System.out.println( Thread.currentThread() + " done");

    }

    public static void main( String[] args ) throws InterruptedException {

	/* Create some threads that will update the same field. */
	UpdateMe um = new UpdateMe();
	SynchRacer r = new SynchRacer( um );
	Thread theThreads[] = new Thread[5];

	System.out.println( "before update, value = " + um.getValue() );

	for(int i=0; i<theThreads.length; i++) {
	    theThreads[i] = new Thread( r );
	    theThreads[i].start();
	}

	/* Wait for all threads to finnish. */
	for(int i=0; i<theThreads.length; i++) {
	    theThreads[i].join();
	}

	System.out.println( "after update, value = " + um.getValue() );
	
    }

}

/**
 * A simple class with one field that is used to illustrate a race condition.
 */
class UpdateMe {
    private int value = 0;
    
    /**
     * Adds to the value.
     */
    public synchronized void addToValue( int i ) {
	int v = value;
	v += i;
	value = v;
    }

    /**
     * Returns the value.
     */
    public int getValue() {
	return value;
    }

}