java线程－自旋锁的实现

public class SpinLock implements Lock {
	
	private final AtomicReference owner = new AtomicReference();

	private AtomicInteger holdCount = new AtomicInteger(1);

	public void lock() {
		if (owner.get() == Thread.currentThread()) {
			holdCount.incrementAndGet();
			return ;
		}
		while (!owner.compareAndSet(null, Thread.currentThread())) {

		}
		holdCount.set(1);
	}

	public void lockInterruptibly throws InterruptedException {
		if (owner.get() == Thread.currentThread()) {
			holdCount.incrementAndGet();
			return ;
		}
		while (!(owner.compareAndSet(null, Thread.currentThread()))) {
			if (owner.isInterrupted()) {
				owner.interrupt();
			}
		}
		holdCount.set(1);
	}

	public boolean tryLock() {
		if (owner == Thread.currentThread()) {
			holdCount.incrementAndGet();
			return true;
		}
		boolean flag = owner.compareAndSet(null, Thread.currentThread());
		if (flag) {
			holdCount.set(1);
		}
		return flag;
	}

	public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {
		if (owner == Thread.currentThread()) {
			holdCount.incrementAndGet();
			return true;
		}
		long start = System.nanoTime();
		long timeout = unit.toNanos(time);
		while (!owner.compareAndSet(null, Thread.currentThread)) {
			if (owner.isInterrupted()) {
				owner.interrupt();
			} 
			long elapsedTime = System.nanoTime() - start;
			if (elapsedTime >= timeout) {
				return false;
			}
		}
		holdCount.set(1);
		return true;
	}

	public void unlock() {
		if (owner != Thread.currentThread())
			throw new IllegalMonitorStateException();
		if (--holdCount == 0) {
			owner.set(null);
		}
	}
}