class SafeRace extends Thread {
    private int count;
    private SafeAccumulate acc;

    public SafeRace( int count, SafeAccumulate acc ) {
	this.count = count;
	this.acc = acc;
    }
    public void run() {
	for( int i = 0; i < count ; i++ ) {
	    acc.inc();
	}
    }
    public static void main( String[] args )  {
        if ( args.length != 1 ) {
            System.out.println("java SafeRace loops");
            System.exit( 1 );
        }
        int loops = Integer.parseInt( args[0] );
        long t = System.currentTimeMillis();
	SafeAccumulate acc = new SafeAccumulate( loops );
	Thread t1 = new SafeRace( 9000, acc );
	Thread t2 = new SafeRace( 8000, acc );
	t1.start();
	t2.start();
	try {
	    t1.join();
	    t2.join();
	}
	catch( InterruptedException ex ) {
	}
	System.out.println( acc.getCount() + " == " + 17000 );
        t = System.currentTimeMillis() - t;
	System.out.println( "elapsed = " + t );
    }
}

class SafeAccumulate {
    private int sum;
    private int loops;

    public SafeAccumulate(int loops ) {
	this.sum = 0;
        this.loops = loops;
    }
    // the only difference is synchronized
    public synchronized void inc() {
	int s = sum;
	for( int i = 0 ; i < loops ; i++ ) 
	    ; // do nothing
	sum = s + 1;
    }
    public int getCount() {
	return sum;
    }
}