class ALock implements Lock {
	ThreadLocal<Integer> mySlotIndex = new ThreadLocal<Integer> (){
		protected Integer initialValue(){
			return 0;
		}
	};
	AtomicInteger tail;
	PaddedPrimitiveNonVolatile<Boolean>[] flag;
	PaddedPrimitive<Boolean> memFence = new PaddedPrimitive<Boolean>(false);
	int size;

	public ALock(int capacity){
		size = capacity;
		tail = new AtomicInteger(0);
		flag = (PaddedPrimitiveNonVolatile<Boolean>[]) new PaddedPrimitiveNonVolatile[capacity];
		for (int i = 0; i < capacity; i++)
		{
			flag[i] = new PaddedPrimitiveNonVolatile<Boolean>(false);
		}
		flag[0].value = true;
		memFence.value = true;
	}
	public void lock(){
		int slot = tail.getAndIncrement() % size;
		mySlotIndex.set(slot);
		while(! flag[slot].value) {};
	}
	public void unlock(){
		int slot = mySlotIndex.get();
		flag[slot].value = false;
		flag[(slot+1)%size].value = true;
		memFence.value = true;
	}
	@Override
	public boolean tryLock() {
		int slot = tail.get() % size;

	    if( flag[slot].value ) {    // check first if it the lock is free
	        this.lock();      // grab it
	        return true;
	      }
	    else
	        return false;
	}
}