手写自旋锁——SpinLock

手写自旋锁

import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.locks.ReentrantLock;

public class SpinLock {
    AtomicReference<Thread> atomicReference = new AtomicReference<>();

    public void lock() {
        Thread thread = Thread.currentThread();
        while (!atomicReference.compareAndSet(null, thread)) {}

    }

    public void unlock() {
        Thread thread = Thread.currentThread();
        atomicReference.compareAndSet(thread, null);
    }
}

使用自旋锁

import java.util.concurrent.TimeUnit;

public class SpinLockTest {
    public static void main(String[] args) {
        SpinLock lock = new SpinLock();
        new Thread(() -> {
            lock.lock();
            try {
                TimeUnit.SECONDS.sleep(3);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            lock.unlock();
        }).start();

        new Thread(() -> {
            lock.lock();
            try {
                TimeUnit.SECONDS.sleep(3);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            lock.unlock();
        }).start();
    }
}

自旋锁的优缺点

• 自旋锁是反复检查锁变量是否可用，因此也是一个忙等待
• 自旋锁节省了线程上下文的切换
• 自旋锁会导致CPU增加负担
• 自旋锁一般用于会堵塞时间短的操作

此处锁的对象是当前线程，是为了方式其他线程解锁