用Java原子变量的CAS方法实现一个自旋锁

实现：

package sjq.mylock;

import java.util.concurrent.atomic.AtomicReference;

public class SpinLock {
    private AtomicReference<Thread> owner = new AtomicReference<>(); //不调用有参构造函数，则实例为null

    public void lock(){
        Thread currentThread = Thread.currentThread();
        while(!owner.compareAndSet(null, currentThread)){  // owner == null ，则compareAndSet返回true，否则为false。
            //拿不到owner的线程，不断的在死循环
        }
    }

    public void unLock(){
        owner.set(null);
        // 也可以这样写，太麻烦，没必要
        /*
        Thread cur = Thread.currentThread();  
        owner.compareAndSet(cur, null);
         */
    }

}

 

 

测试：

package sjq.mylock;

import java.util.concurrent.CountDownLatch;

import org.junit.Test;

public class TestSpinLock {

    final static int THREAD_NUM = 100;
    static int x = 0;

    @Test
    public void testLock() throws InterruptedException {
        CountDownLatch latch = new CountDownLatch(THREAD_NUM);

        // 锁
        SpinLock spinLock = new SpinLock();

        for (int i = 0; i < THREAD_NUM; i++) {
            // 启动子线程
            new Thread(() -> {

                // 每个线程循环多次，频繁上锁，解锁。
                for (int n = 0; n < 100; n++) {
                    spinLock.lock();
                    x++;
                    spinLock.unLock();
                }

                latch.countDown();    // 子线程通知主线程，工作完毕。
            }).start();
        }
        latch.await();    // 主线程等待所有子线程结束。

        System.out.println(x);    // 最终打印结果：10000 ，未出现线程不安全的异常。
    }
}