具有单独读取器和写入器线程的单个队列是否需要锁定？

Question

I have a shared queue (implemented using a singleton queue wrapper) and a reader thread and a writer thread. I also have a mechanism to inform the reader thread when writer thread adds elements (enqueue) to the queue. Reader thread dequeue only one element when informed. Is there a necessity of a Read Write Lock in this scenario.

Since writer is only enqueing and reader dequeing I feel like there is no need for a lock, if reader checks the queue size when dequeing.

Answer 1

I assume you mean a stl::queue and no most operations on stl containers are not thread save. For an discussion on exceptions see C++11 STL containers and thread safety . STL prefers speed over security (eg range check for array indices etc.) assuming that developers will implement their own checks.

Answer 2

Since writer is only enqueing and reader dequeing I feel like there is no need for a lock, if reader checks the queue size when dequeing.

Among other problems that operation alone is already unsafe, when the queue is modified by another thread. In c++, any unsynchronized access to a non-atomic shared variable (with at least one of them is a write) is a data race and hence UB.