自旋锁 SPIN LOCK
当线程尝试获取某个锁时，如果该锁已被其他线程占用，就一直循环检测锁是否被释放，而不是进入线程挂起或睡眠状态。
自旋锁适用于锁竞争不激烈很快能获取到锁的场景
否则会陷入长时间的循环检测等待，白白消耗cpu


简单实现关键代码

private AtomicReference owner = new AtomicReference();

	public void lock() {
		Thread currentThread = Thread.currentThread();
		// 抢占锁成功，设置当前线程为锁的拥有者
		while (!owner.compareAndSet(null, currentThread)) {
		}
	}

	public void unlock() {
		Thread currentThread = Thread.currentThread();
		// 只有锁的拥有者才能释放锁
		owner.compareAndSet(currentThread, null);
	}

测试输出结果

thread-5 get lock success,1557290490243
thread-5 run done,time=40,1557290490287


thread-3 get lock success,1557290490287
thread-3 run done,time=230,1557290490522


thread-6 get lock success,1557290490522
thread-6 run done,time=380,1557290490902


成对输出 



简单实现及测试完整代码




import java.util.Random;
import java.util.concurrent.atomic.AtomicReference;

public class SimpleSpinLock {

	private static final SimpleSpinLock lock = new SimpleSpinLock();

	private static final Random rand = new Random();

	public static void main(String[] args) throws Exception {
		
		int num = 10;
		
		for(int i=0;i owner = new AtomicReference();

	public void lock() {
		Thread currentThread = Thread.currentThread();
		// 抢占锁成功，设置当前线程为锁的拥有者
		while (!owner.compareAndSet(null, currentThread)) {
		}
	}

	public void unlock() {
		Thread currentThread = Thread.currentThread();
		// 只有锁的拥有者才能释放锁
		owner.compareAndSet(currentThread, null);
	}

	private static class SpinLockTestThread extends Thread {

		public SpinLockTestThread(int index) {
			setName("thread-" + index);
		}

		public void run() {

			while (true) {
				lock.lock();
				System.out.println(getName()+" get lock success,"+System.currentTimeMillis());
				try {
					// 模拟业务方法执行耗时
					long time = 5 + rand.nextInt(500);
					Thread.sleep(time);
					System.out.println(getName()+" run done,time="+time+","+System.currentTimeMillis()+"\n\n");
				} catch (Throwable e) {
					System.out.println(getName()+" run error,"+System.currentTimeMillis()+","+e+"\n\n");	
				}
				
				lock.unlock();
			}
		}
	}

}