C++ Mutable Mutex

Question

I have multi threading program with enable state and queue concurently, so i will use mutex method like bellow

{std::lock_guard<std::mutex> lock_en(eventLogMutex);en = enable;}

my question, should i use different mutex lock guard for enable and queue, like

{
  std::lock_guard<std::mutex> lock_queue(eventLogMutex);
  ....
}

and

{
  std::lock_guard<std::mutex> lock_en(eventLogMutex);
  ...
}

Thank's

Answer 1

Yes, you should. A lock_guard relies on RAII to lock and unlock the mutex - when it goes out of scope, the mutex is automatically released. If you make the lock_guard a member variable, using it will be pointless. You should define the lock_guard in a scope as closest to the protected code as possible - initialize it right before you actually need the lock, and have it go out of scope right after you're done with the mutex.