Java中常见的锁-----＞自旋锁_java 常见的自旋锁-优快云博客

本文链接：https://blog.youkuaiyun.com/NotRepent/article/details/124278462

本文探讨了自旋锁的概念，展示了Java Unsafe中的getAndAddInt方法，并手写了自旋锁示例。通过AtomicReference实现线程安全的锁，以减少上下文切换。同时介绍了如何在多线程环境中使用SplitLockDemo进行同步操作。

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自旋锁

是指尝试获取锁的线程不会立即被阻塞而是采用循环的方式去获取锁，这样的好处是减少上下文切换消耗，缺点是循环会消耗CPU...

Unsafe

 public final int getAndAddInt(Object var1, long var2, int var4) {
        int var5;
        do {
            var5 = this.getIntVolatile(var1, var2);
        } while(!this.compareAndSwapInt(var1, var2, var5, var5 + var4));

        return var5;
    }

手写自旋锁

上代码

package com.example.demo;

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

public class SplitLockDemo {

    //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 invock MyUnLock");
    }

    public static void main(String[] args) {

        SplitLockDemo splitLockDemo = new SplitLockDemo();
        new Thread(() -> {
            try {
                splitLockDemo.myLock();
                try {
                    TimeUnit.SECONDS.sleep(5);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
            splitLockDemo.MyUnLock();
        }, "AAA").start();

        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (Exception e) {
            e.printStackTrace();
        }

        new Thread(() -> {
            try {
                splitLockDemo.myLock();
                 try {
                       TimeUnit.SECONDS.sleep(1);
                      } catch (Exception e) {
                       e.printStackTrace();
                   }
                splitLockDemo.MyUnLock();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }, "BBB").start();
    }
}