加深对AQS原理的理解示例二：自己设计一个同步工具，同一时刻最多只有两个线程能访问，超过线程将被阻塞

/**
 *@Desc 设计一个同步工具，同一时刻最多只有两个线程能访问，超过线程将被阻塞<br>
 *     思路分析：
 *     1.共享锁 两个线程及以内能成功获取到锁
 *     2.
 *@Author zhangfengshi
 *@Date 2021/4/5 3:26 下午
 *@Version 1.0
 */
public class TwinsLock implements Lock {

    public Sync sync=new Sync(2);

    public static class Sync extends AbstractQueuedSynchronizer {

        public Sync(int count){
            if(count<=0){
                throw new RuntimeException("error");
            }
            setState(count);
        }

        /**
         *
         * @param reduceCount
         * @return -1获取共享锁失败 0-只能成功一次 后续将获取失败 正数-可以获取锁
         */
        @Override
        protected int tryAcquireShared(int reduceCount) {

            for(;;){
                int currentCount=this.getState();
                int newCount=currentCount-reduceCount;
                //newCount<0代表currentCount=0
                if(newCount<0||compareAndSetState(currentCount,newCount)){
                    return newCount;
                }
            }
        }

        @Override
        protected boolean tryReleaseShared(int returnCount) {
            for(;;){
                int currentCount=this.getState();
                int newCount=currentCount+returnCount;
                if(compareAndSetState(currentCount,newCount)){
                    return true;
                }
            }
        }
    }
    @Override
    public void lock() {
        sync.acquireShared(1);
    }
    @Override
    public void unlock() {
        sync.releaseShared(1);
    }
    @Override
    public void lockInterruptibly() throws InterruptedException {

    }

    @Override
    public boolean tryLock() {
        int result= sync.tryAcquireShared(1);
        return result>0;
    }

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

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

}