手写了一个锁

十月 20, 2020 2215

尝试着用park+自旋手写实现一把锁

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public class syncTest {
     static volatile  int status = 0;
     static Queue<Thread> parkQueue = new LinkedList<>();

    public static void main(String[] args) {
        Thread t1 = new Thread(){
            @Override
            public void run() {
                synctest();
            }
        };


        Thread t2 = new Thread(){
            @Override
            public void run() {
                synctest();
            }
        };

        t1.setName("t1");
        t2.setName("t2");
        t1.start();
//        try {
//            Thread.sleep(2000);
//        } catch (InterruptedException e) {
//            e.printStackTrace();
//        }
        t2.start();

        System.out.println("ThreadMain-----------");
    }

    //自旋  上锁 让出内存
    public static void lock() {
        while(!compareAndSet(0,1)){
            park();
        }
    }
    //唤醒
    public static void unlock(){
        status = 0;
        lock_notify();
    }
    //阻塞线程并将阻塞线程写入队列
    public static void park(){
        parkQueue.offer(Thread.currentThread());
        LockSupport.park();
    }
    //从队列里拿出线程并唤醒 再次尝试获得锁
    private static void lock_notify() {
        if(parkQueue.size() != 0){
            Thread t = parkQueue.poll();
            LockSupport.unpark(t);
        }

    }

    private static boolean compareAndSet(int i, int j) {
        if(status == i){
            status = j;
            return true;
        }else{
            return false;
        }
    }

    //测试方法
    public static void synctest() {
        lock();
        System.out.println(Thread.currentThread().getName() +"-------st");
        try {
            Thread.sleep(8000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        System.out.println(Thread.currentThread().getName() +"-------ed");
        unlock();
    }
}

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