自旋锁

自旋锁

• A线程进来没问题，不解锁的情况下，B线程进来会空循环等待A解锁

package Lock.SpinlockDemo;

import java.util.concurrent.atomic.AtomicReference;

public class SpinlockA {
    // int 0
    //thread  null
    AtomicReference<Thread> atomicReference = new AtomicReference<>();

    //加锁
    public void lock() {
        Thread thread = Thread.currentThread();
        //自旋锁
        // compareAndSet() 如果符合条件，就会set值。
        // 返回true set成功
        // 返回false 没set
        boolean setSuccessful = atomicReference.compareAndSet(null, thread);
        while (!setSuccessful) {
            //第二个线程进来，setSuccessful为false，一直空循环
        }
        System.out.println(Thread.currentThread().getName() + "-->myLock");
    }

    //解锁
    public void unlock() {
        Thread thread = Thread.currentThread();
        System.out.println(Thread.currentThread().getName() + "-->myUnLock");

        atomicReference.compareAndSet(thread, null);
    }
}

package Lock.SpinlockDemo;

import java.util.concurrent.TimeUnit;

public class Test {
    public static void main(String[] args) throws InterruptedException {
        SpinlockA spinlockA = new SpinlockA();

        new Thread(() -> {
            spinlockA.lock();
            try {
                TimeUnit.SECONDS.sleep(3);
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                spinlockA.unlock();
            }
        }, "A").start();

        TimeUnit.SECONDS.sleep(1);
        new Thread(() -> {
            spinlockA.lock();
            try {
                TimeUnit.SECONDS.sleep(1);
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                spinlockA.unlock();
            }
        }, "B").start();
    }
}