深入理解Java中的锁（二）

public class GetLockDemo {
  // 公平锁  // static Lock lock =new ReentrantLock(true);
  // 非公平锁  static Lock lock = new ReentrantLock();
  public static void main(String[] args) throws InterruptedException {
    // 主线程 拿到锁    lock.lock();
    Thread thread =
        new Thread(
            () -> {
              // 子线程 获取锁（不死不休）              System.out.println("begain to get lock...");
              lock.lock();
              System.out.println("succeed to get lock...");
              //              // 子线程 获取锁(浅尝辄止)
              //              boolean result = lock.tryLock();
              //              System.out.println("是否获得到锁：" + result);
              //
              //              // 子线程 获取锁(过时不候)
              //              try {
              //                boolean result1 = lock.tryLock(5, TimeUnit.SECONDS);
              //                System.out.println("是否获得到锁：" + result1);
              //              } catch (InterruptedException e) {
              //                e.printStackTrace();
              //              }
              //
              //              // 子线程 获取锁（任人摆布）              //              try {
              //                System.out.println("start to get lock Interruptibly");
              //                lock.lockInterruptibly();
              //              } catch (InterruptedException e) {
              //                e.printStackTrace();
              //                System.out.println("dad asked me to stop...");
              //              }
            });
    thread.start();
    Thread.sleep(10000L);
    lock.unlock();
  }
}

public class ConditionDemo {
  static Lock lock = new ReentrantLock();
  static Condition condition = lock.newCondition();
  public static void main(String[] args) throws InterruptedException {
    Thread thread =
        new Thread(
            () -> {
              lock.lock();
              System.out.println("condition.await()");
              try {
                condition.await();
                System.out.println("here i am...");
              } catch (InterruptedException e) {
                e.printStackTrace();
              } finally {
                lock.unlock();
              }
            });
    thread.start();
    Thread.sleep(2000L);
    lock.lock();
    condition.signalAll();
    lock.unlock();
  }
}

public class MyReentrantLock implements Lock {
  // 标记重入次数的count值  private AtomicInteger count = new AtomicInteger(0);
  // 锁的拥有者  private AtomicReference<Thread> owner = new AtomicReference<>();
  // 等待队列  private LinkedBlockingDeque<Thread> waiters = new LinkedBlockingDeque<>();
  @Override
  public boolean tryLock() {
    // 判断count是否为0，若count！=0，说明锁被占用    int ct = count.get();
    if (ct != 0) {
      // 判断锁是否被当前线程占用，若被当前线程占用，做重入操作，count+=1
      if (owner.get() == Thread.currentThread()) {
        count.set(ct + 1);
        return true;
      } else {
        // 若不是当前线程占用，互斥，抢锁失败，return false
        return false;
      }
    } else {
      // 若count=0， 说明锁未被占用，通过CAS（0，1） 来抢锁      if (count.compareAndSet(ct, ct + 1)) {
        // 若抢锁成功，设置owner为当前线程的引用        owner.set(Thread.currentThread());
        return true;
      } else {
        return false;
      }
    }
  }
  @Override
  public void lock() {
    // 尝试抢锁    if (!tryLock()) {
      // 如果失败，进入等待队列      waiters.offer(Thread.currentThread());
      // 自旋      for (; ; ) {
        // 判断是否是队列头部，如果是        Thread head = waiters.peek();
        if (head == Thread.currentThread()) {
          // 再次尝试抢锁          if (!tryLock()) {
            // 若抢锁失败，挂起线程，继续等待            LockSupport.park();
          } else {
            // 若成功，就出队列            waiters.poll();
            return;
          }
        } else {
          // 如果不是队列头部，就挂起线程          LockSupport.park();
        }
      }
    }
  }
  public boolean tryUnlock() {
    // 判断，是否是当前线程占有锁，若不是，抛异常    if (owner.get() != Thread.currentThread()) {
      throw new IllegalMonitorStateException();
    } else {
      // 如果是，就将count-1  若count变为0 ，则解锁成功      int ct = count.get();
      int nextc = ct - 1;
      count.set(nextc);
      // 判断count值是否为0
      if (nextc == 0) {
        owner.compareAndSet(Thread.currentThread(), null);
        return true;
      } else {
        return false;
      }
    }
  }
  @Override
  public void unlock() {
    // 尝试释放锁    if (tryUnlock()) {
      // 获取队列头部， 如果不为null则将其唤醒      Thread thread = waiters.peek();
      if (thread != null) {
        LockSupport.unpark(thread);
      }
    }
  }
  @Override
  public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {
    return false;
  }
  @Override
  public void lockInterruptibly() throws InterruptedException {}
  @Override
  public Condition newCondition() {
    return null;
  }
}