Android Lock锁实现原理详细分析

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
            }
        }
    }

public interface Lock {
    // 加锁
    void lock()；
    // 尝试获取锁
    boolean tryLock();
    boolean tryLock(long time, TimeUnit unit) throws InterruptedException;
    // 解锁
    void unlock();
}

    // 默认构造方法，非公平锁
    public ReentrantLock() {
        sync = new NonfairSync();
    }
    // 构造方法，公平锁
    public ReentrantLock(boolean fair) {
        sync = fair ? new FairSync() : new NonfairSync();
    }
    // 加锁
    public void lock() {
        sync.lock();
    }