C++11 reentrant class locking strategy

Question

I have an interface using the pimpl idiom, however the interface needs to be reentrant. Calling threads do not need to be aware of the locking, however. This is

Answer 1

Using a Pimpl idiom, the mutex should be part of the implementation. This will let you to master when the lock is started.

BTW, why using a unique_lock when a lock_guard will be enough?

I don't see any advantage to make impl public.

std::unique_ptr should be as efficient as a pointer for most of the moderns compilers. Not verified however.

I would forward the const char[N] foo_set not as

  template
  bool foo_set(const char (&new_val)[N]) { return foo_set(std::string(new_val, N)); }

but like

  template
  bool foo_set(const char (&new_val)[N]) { return foo_set(N, new_val); }

This avoids the string creation on the header file and let the implementation do whatever is needed.