import java.util.concurrent.TimeUnit;

import java.util.concurrent.locks.AbstractQueuedSynchronizer;

import java.util.concurrent.locks.Condition;

import java.util.concurrent.locks.Lock;

public class MyLock implements Lock {

    private Helper helper = new Helper();

    @Override

    public void lock() {

        helper.acquire(1);

    }

    @Override

    public void lockInterruptibly() throws InterruptedException {

        helper.acquireInterruptibly(1);

    }

    @Override

    public boolean tryLock() {

        return helper.tryAcquire(1);

    }

    @Override

    public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {

        return helper.tryAcquireNanos(1, unit.toNanos(time));

    }

    @Override

    public void unlock() {

        helper.release(1);

    }

    @Override

    public Condition newCondition() {

        return helper.newCondition();

    }

    private class Helper extends AbstractQueuedSynchronizer {

        @Override

        protected boolean tryAcquire(int arg) {

            //如果第一个线程进来，可以拿到锁，返回true

            //如果第二个线程进来，拿不到锁，返回false,有种特例，如果当前进来的线程和当前保存的线程是同一个线程，则可以拿到锁，但是要更新状态值

            //如何判断是第一个线程进来还是其他线程进来

            int state = getState();

            Thread t = Thread.currentThread();

            if (state == 0) {//判断是否是第一个线程

                if (compareAndSetState(0, arg)) {

                    setExclusiveOwnerThread(Thread.currentThread());

                    return true;

                }

            } else if(getExclusiveOwnerThread() == t) {//判断当前进来的线程和当前保存的线程是否是同一个线程，实现重入锁，因为锁的是对象，所以只要是同一个Helper对象线程就是同一个线程

                setState(state + 1);

                return true;

            }

            return false;

        }

        @Override

        protected boolean tryRelease(int arg) {

            //锁的获取和释放肯是一一对应的，那么调用此方法的线程一定是当前线程

            if (Thread.currentThread() != getExclusiveOwnerThread()) {

                throw new RuntimeException();

            }

            int state = getState() - arg;

            setState(state);

            if (state == 0) {

                setExclusiveOwnerThread(null);

                return true;

            }

            return false;

        }

        protected ConditionObject newCondition() {

            return new ConditionObject();

        }

    }

}

public class TestMyLock {

    private int value;

    private MyLock myLock = new MyLock();

    public int getValue() {

        myLock.lock();

        try {

            Thread.sleep(10);

        } catch (InterruptedException e) {

            e.printStackTrace();

        }

        value ++;

        myLock.unlock();

        return value;

    }

    public void a() {

        myLock.lock();

        System.out.println("a");

        b();

        myLock.unlock();

    }

    public void b() {

        myLock.lock();

        System.out.println("b");

        myLock.unlock();

    }

    public static void main(String[] args) {

        TestMyLock testMyLock = new TestMyLock();

        //检测是否会并发

        Runnable runnable = () -> {

          for (int i = 0; i<100; i++) {

              System.out.println(Thread.currentThread().getId()+",值：" + testMyLock.getValue());

          }

        };

        new Thread(runnable).start();

        new Thread(runnable).start();

        new Thread(runnable).start();

        //检测重入锁

        Runnable runnable1 = () -> testMyLock.a();

        new Thread(runnable1).start();

    }

}