http://stackoverflow.com/questions/20516773/stdunique-lockstdmutex-or-stdlock-guardstdmutex

 

The difference is that you can lock and unlock a std::unique_lock. std::lock_guard will be locked only once on construction and unlocked on destruction.

So for usecase B you definitely need a std::unique_lock for the condition variable. In case A it depends whether you need to relock the guard.

std::unique_lock has other features that allow it to e.g.: be constructed without locking the mutex immediately but to build the RAII wrapper (see ).

Lock guards can be used when you simply need a wrapper for a limited scope, e.g.: a member function:

void member_foo() { std::lock_guard
    
      lock(this->my_mutex); ... }
    

To clarify a question by chmike, by default std::lock_guard and std::unique_lock are the same. So in the above case, you could replace std::lock_guard with std::unique_lock. However, std::unique_lock might have a tad more overhead.