简单实现自己的显示锁

你的名字 2022-11-29 03:05 94阅读 0赞

## 实现的目标 ##

**实现自己的锁，使线程同步。提供了两个lock方法一个带有参数（timeout）当固定时间内没有执行的线程就不让他去执行了。**  
1.创建接口 Lock定义了超时异常，当等待强锁的时间超过timeout让他超时异常

public interface Lock { 
        class TimeoutException extends Exception{ 
            TimeoutException(String message){ 
                super(message);
            }
        }
    
        void lock() throws InterruptedException;
    
        void lock(long timeout) throws InterruptedException, TimeoutException;
    
        void unlock();
    }

2.创建接口的实现类MyLock

> 定义有个waitSet来存放阻塞线程。定义isHold来决定是不是当前的锁已经被持有了。当isHold为true表示当前的显示锁被拿走了，其他线程就得等着进入waitSet队列。当线程拿到锁了，就立刻将isHold给置为true  
> 在释放锁的时候就需要将所有线程notify()让其他线程争抢显示锁。（其实就是通过isHold中间变量来控制是不是拿到锁了！为什么不用volatile？肯定要给方法加锁防止逻辑乱掉，加锁方法里面就不用volatile了啊）

public class MyLock implements Lock { 
        private boolean isHold = false;
    
        private final List<Thread> WAIT_SET = new LinkedList<>();
    
        private Thread currentThread;
    
        @Override
        public synchronized void lock() throws InterruptedException { 
    
            while(isHold){ 
                this.wait();
                WAIT_SET.add(Thread.currentThread());
            }
            currentThread = Thread.currentThread();
            WAIT_SET.remove(Thread.currentThread());
            isHold = true;
    
        }
    
        @Override
        public synchronized void lock(long timeout) throws InterruptedException,TimeoutException { 
            Long hasRmaining = timeout;
            Long endTime = System.currentTimeMillis() + timeout;
            while(isHold){ 
                if(hasRmaining <= 0)
                { 
                    throw new TimeoutException("超时异常");
                }
                WAIT_SET.add(Thread.currentThread());
                this.wait(timeout);
                hasRmaining = endTime - System.currentTimeMillis();
            }
            WAIT_SET.remove(Thread.currentThread());
            currentThread = Thread.currentThread();
            isHold = true;
        }
    
        public Collection getWitSet(){ 
            return Collections.unmodifiableCollection(WAIT_SET);
        }
        @Override
        public synchronized void unlock() { 
            if(currentThread == Thread.currentThread()){ 
                isHold = false;
                this.notifyAll();
            }
    
        }
    }