Question

我在采访中被问到这个问题：伪代码是好的

//Assume you have a list or A Queue
//1 - How do you make Sure pushing to list is safe?
//1 - My Ans: 
        void push(Element e){
            Synchronized(this){
               list.push(e);
              }
             }
//2- Interviewer said Ok, there is better way to do this without Synchronized word
          void push(Element e){
              writeLock.Lock();
              list.push(e);
              writeLock.UnLock();
             }
//3- He said Ok, but wouldn't work if there are 16 threads, How can I make sure only one thread can write?  His answer was more like a "Semaphore"
       void push(Element e){
             readLock.lock(16), //meaning get read lock on all 16 thrds
              writeLock.Lock(); //then allow to write
              list.push(e);
              writeLock.UnLock();
              readLock.Unlock()
             }

我不确定我是否理解他在＃3的解决方案，任何人都需要解释和阐述？

Answer 1

理念是读者只有在没有写入的情况下才能阅读。换句话说，读取是无同步的。所以16个线程可以同时读取。但是，当您想要写入时，锁定所有内容（读取和写入过程）并仅执行写入操作。 Interviewer可能已经从ConcurrentHashMap中获取了这个想法，因为concurrencyLevel的默认值是16。

我建议您查看http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ConcurrentHashMap.html

在Java（面试）中使用Locks的最佳实践是什么？

1 个答案: