浅析JAVA Lock锁原理

static Lock lock = new ReentrantLock();public static void main(String[] args) throws InterruptedException {


    lock.lock();//其他没拿到锁的卡住不动

    Thread thread = new Thread(new Runnable() {
      @Override
      public void run() {
        System.out.println("start to get lock Interruptibly");
        lock.unlock(); //看看会发生什么，注释掉再看看
        lock.lock();
        System.out.println("拿到锁");
        lock.unlock();
        System.out.println("释放锁");
      }
    });
    thread.start();

    Thread.sleep(3000);
    lock.unlock();
  }

public class MyLock implements Lock {
  //多并发调用 0-未占用 大于0-占用
  AtomicInteger state = new AtomicInteger();

  Thread ownerThread = new Thread();

  //等待锁的队列
  LinkedBlockingQueue<Thread> waiters = new LinkedBlockingQueue();

  @Override
  public void lock() {
    if (!tryLock()) { //先抢锁，所以是非公平锁
      //没拿到锁,放到队列中去进行排队
      waiters.add(Thread.currentThread());
      //等待被唤醒
      for (; ; ) {
        if (tryLock()) { //非公平锁情况下，唤醒过来继续获取锁
          waiters.poll(); //获取锁成功把自己从队列中取出来
          return;
        } else  //获取锁失败
          LockSupport.park(); //线程阻塞
      }
    }
  }


  @Override
  public boolean tryLock() {
    if (state.get() == 0) { //如果锁没被占用
      if (state.compareAndSet(0, 1)) { //如果成功拿到锁
        ownerThread = Thread.currentThread();  //占用锁线程改为当前线程
        return true;
      }
    }
    return false;
  }

  @Override
  public void unlock() {

    if (ownerThread != Thread.currentThread()) //占用锁线程不是当前线程无法释放锁
      throw new RuntimeException("非法调用,当前锁不属于你");

    if (state.decrementAndGet() == 0) //如果成功释放锁
      ownerThread = null; //占用锁线程置空
    //通知其他线程
//    Thread thread = null;
//
//    while ((thread = waiters.peek()) != null)
//      LockSupport.unpark(thread);
    Thread thread = waiters.peek(); //获取队列头部线程，线程还留在队列中
    if (thread != null) {
      LockSupport.unpark(thread); //取消阻塞
    }
  }



  @Override
  public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {
    return false;
  }


  @Override
  public Condition newCondition() {
    return null;
  }

  @Override
  public void lockInterruptibly() throws InterruptedException {

  }
}

@Override
  public void lock() {
    checkQueue（）;//线程来的时候先不获取锁，而是先检查队列中有没有等待的线程，如果有，直接放入队列，如果没有，再去获取锁
    if (!tryLock()) { //先抢锁，所以是非公平锁
      //没拿到锁,放到队列中去进行排队
      waiters.add(Thread.currentThread());
      //等待被唤醒
      for (; ; ) {
        if (tryLock()) { //非公平锁情况下，唤醒过来继续获取锁
          waiters.poll(); //获取锁成功把自己从队列中取出来
          return;
        } else  //获取锁失败
          LockSupport.park(); //线程阻塞
      }
    }
  }