JUC之自旋锁

谁借莪１个温暖的怀抱￠ 2023-06-21 07:17 9阅读 0赞

# 自旋锁（spinlock）： #

是指尝试获取锁的线程不会立即阻塞，而是采用循环的方式去尝试获取锁，这样的好处是减少线程上下文切换的消耗，缺点是循环会消耗CPU

问题：手写一个自旋锁

题目：实现一个自旋锁

自旋锁好处：循环比较获取直到成功为止，没有类似wait的阻塞

通过CAS操作完成自旋锁，A线程先进来调用myLock方法自己持有锁5秒钟，B随后进来后发现

当前有线程持有锁，不是null，所以只能通过自旋等待，直到A释放锁后B随后抢到。

### 代码 ###

package Lock;
    
    import java.util.concurrent.TimeUnit;
    import java.util.concurrent.atomic.AtomicReference;
    
    public class SpinLockDemo {
    
        //原子引用类
        AtomicReference<Thread> atomicReference=new AtomicReference<>();
    
        public  void myLock(){
            Thread thread =Thread.currentThread();
            System.out.println(Thread.currentThread().getName() + "\t come in 0(n_n)0");
            while (atomicReference.compareAndSet(null,thread)){
    
            }
        }
    
        public  void myUnlock(){
            Thread thread =Thread.currentThread();
            atomicReference.compareAndSet(thread,null);
            System.out.println(Thread.currentThread().getName() + "\t invoked myUnLock()");
        }
        public static void main(String[] args) {
        SpinLockDemo spinLockDemo =new SpinLockDemo();
    
        new Thread(()->{
            spinLockDemo.myLock();
            try {
                TimeUnit.SECONDS.sleep(5);
            }catch (InterruptedException e){e.printStackTrace();}
            spinLockDemo.myUnlock();
        },"AA").start();
            try {
                TimeUnit.SECONDS.sleep(3);
            }catch (InterruptedException e){e.printStackTrace();}
    
    
            new Thread(()->{
                spinLockDemo.myLock();
                spinLockDemo.myUnlock();
            },"BB").start();
    
        }
    }

AA	 come in 0(n_n)0
    BB	 come in 0(n_n)0
    BB	 invoked myUnLock()
    AA	 invoked myUnLock()
    
    Process finished with exit code 0