class Peterson {
    // thread-local index, 0 or 1
    private var flag:Array[Boolean]{self.rank==1};
    private var victim:Int;
    
    public def this() {
	flag = new Array[Boolean](2,false);
	victim = 0;
    }

    public def lock(i:Int) {
	assert(i ==  0 | i == 1);
	val j:Int = 1 - i;
	flag(i) = true;                    // I'm interested
	victim = i;                        // you go first
	while (flag(j) && victim == i) {}; // wait
  }
    
    public def unlock(i:Int) {
	flag(i) = false;
    }
}