Java锁之自旋锁

向右看齐 2022-01-26 03:11 334阅读 0赞

# Java锁之自旋锁 #

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## 目录 ##

1.  java锁之自旋锁理论知识
2.  java锁之自旋锁代码验证

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### 1. java锁之自旋锁理论知识 ###

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1.  自旋锁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

### 2. java锁之自旋锁代码验证 ###

代码验证：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，知道A释放锁后B随后抢到。

import java.util.concurrent.TimeUnit;
    import java.util.concurrent.atomic.AtomicReference;
    
    public class SpinLockDemo {
        
        //原子引用线程
        AtomicReference<Thread> atomicReference = new AtomicReference<>();
    
        public void myLock(){
        
            Thread thread = Thread.currentThread();
            System.out.println(Thread.currentThread().getName()+"\t come in ");
            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(1);
            } catch (InterruptedException e) {
        
                e.printStackTrace();
            }
    
            new Thread(() -> {
        
                spinLockDemo.myLock();
                try {
        
                    TimeUnit.SECONDS.sleep(1);
                } catch (InterruptedException e) {
        
                    e.printStackTrace();
                }
                spinLockDemo.myUnlock();
            },"BB").start();
        }
    }

编译结果：

![在这里插入图片描述][20190527235633582.png]

[20190527235633582.png]: /images/20220126/6ecab547cf08434a9f36248a5f99a89e.png