java 自旋锁

基本实现

/**
 * 自旋实现锁
 */
public class MyLock implements ILock {
    private volatile int status = 0;

    public void lock() {
        while (!compareAndSwap(1)) {
            System.out.println(Thread.currentThread().getName() + "waiting");
            //v1  自旋+yeild  让出CPU，还是有很大几率被CPU重新调度，CPU消耗大
            //Thread.yield();
            //sleep + 自旋   让出CPU，但是sleep时长难以确定
            try {
                TimeUnit.MILLISECONDS.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

        }
        System.out.println(Thread.currentThread().getName() + "lock,");
    }

    private boolean compareAndSwap(int newValue) {
        if (0 == status) {
            status = newValue;
            return true;
        }
        return false;
    }

    public void unlock() {
        status = 0;
        System.out.println(Thread.currentThread().getName() + "unlock");
    }
}

park实现

/**
 * park+自旋
 */
public class ParkLock implements ILock {
    private volatile int status = 0;
    private Queue<Thread> queue = new ConcurrentLinkedQueue<>();

    public void lock() {
        while (!compareAndSwap(1)) {
            System.out.println(Thread.currentThread().getName() + "waiting");
            threadPark();
        }
        System.out.println(Thread.currentThread().getName() + "lock,");
    }

    private void threadPark() {
        queue.add(Thread.currentThread());
        status = 1;
        LockSupport.park();
    }

    private boolean compareAndSwap(int newValue) {
        if (0 == status) {
            status = newValue;
            return true;
        }
        return false;
    }

    public void unlock() {
        status = 0;
        Thread poll = queue.poll();
        LockSupport.unpark(poll);
        System.out.println(Thread.currentThread().getName() + "unlock");
    }
}

测试代码

public class CountRun implements Runnable {
    private static ParkLock lock = new ParkLock();
    private final CountDownLatch latch;

    public CountRun(CountDownLatch latch) {
        this.latch = latch;
    }

    @Override
    public void run() {
        lock.lock();
        for (int i = 0; i < 100; i++) {
            CountMain.INIT_VALUE++;
            try {
                Thread.sleep(20);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        lock.unlock();
        latch.countDown();
    }
}

public class CountMain {
    public static int INIT_VALUE = 0;
    public static final int LIMIT = 3;

    public static void main(String[] args) throws InterruptedException {
        CountDownLatch countDownLatch = new CountDownLatch(LIMIT);
        new Thread(new CountRun(countDownLatch)).start();
        new Thread(new CountRun(countDownLatch)).start();
        new Thread(new CountRun(countDownLatch)).start();
        countDownLatch.await();
        System.out.println(Thread.currentThread().getName() + ":" + CountMain.INIT_VALUE);
    }
}