std::unique_lock or std::lock_guard?

Question

I have two use cases.

A. I want to synchronise access to a queue for two threads.

B. I want to synchronise access to a queue for two threads and use a conditio

Answer 1

Use lock_guard unless you need to be able to manually unlock the mutex in between without destroying the lock.

In particular, condition_variable unlocks its mutex when going to sleep upon calls to wait. That is why a lock_guard is not sufficient here.