How to implement a reentrant spin lock in java

Explanation

1. It means that the thread trying to obtain the lock will not be blocked, but will obtain the lock through a loop.

2. Advantages: Reduce the consumption of context switching.

Disadvantages: Loop consumes CPU.

Example

public class ReentrantSpinLock {
 
 
    private AtomicReference<Thread> owner = new AtomicReference<>();
 
    // 可重入次数
    private int count = 0;
 
    // 加锁
    public void lock() {
        Thread current = Thread.currentThread();
        if (owner.get() == current) {
            count++;
            return;
        }
        while (!owner.compareAndSet(null, current)) {
            System.out.println("--我在自旋--");
        }
    }
 
    //解锁
    public void unLock() {
        Thread current = Thread.currentThread();
        //只有持有锁的线程才能解锁
        if (owner.get() == current) {
            if (count > 0) {
                count--;
            } else {
                //此处无需CAS操作，因为没有竞争，因为只有线程持有者才能解锁
                owner.set(null);
            }
        }
    }
 
    public static void main(String[] args) {
        ReentrantSpinLock spinLock = new ReentrantSpinLock();
        Runnable runnable = () -> {
            System.out.println(Thread.currentThread().getName() + "开始尝试获取自旋锁");
            spinLock.lock();
            try {
                System.out.println(Thread.currentThread().getName() + "获取到了自旋锁");
                Thread.sleep(4000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                spinLock.unLock();
                System.out.println(Thread.currentThread().getName() + "释放了了自旋锁");
            }
        };
        Thread thread1 = new Thread(runnable);
        Thread thread2 = new Thread(runnable);
        thread1.start();
        thread2.start();
    }
}

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