import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.TimeUnit;

public class MySpinLock implements Lock {
    private AtomicReference<Thread> held = new AtomicReference<Thread>(null);
    private int count = 0;
    public void lock() {
	Thread me = Thread.currentThread();
	Thread owner = held.get();
	if (owner == me) {
	    count++;
	    return;
	}
	// wait until I am the owner
	while (!held.compareAndSet(null, me));
	// now I am the owner
	count++;
	return;
    }
    public void unlock() {
	Thread me = Thread.currentThread();
	Thread owner = held.get();
	if (owner == me) {
	    count--;
	    if (count == 0)
		held.set(null);
	    return;
	}
	// else do nothing
    }
    public boolean tryLock() { return false; }
    public boolean tryLock(long time, TimeUnit unit) { return false; }
    public Condition newCondition() { return null; }
    public void lockInterruptibly() throws InterruptedException { throw new InterruptedException(); }
}