4 ms·

I'd be very surprised if GCC actually used locks for unique_ptr. A unique_ptr owns the object it points to, so we know for a fact that it doesn't need to check

• throwaway81523 5y ago
  You might be right about that, i.e. I probably derped up. It's been a long while since I looked at it, and the issue might only be with shared_ptr. I'm starting to remember finding out that shared_ptr was surprisingly expensive even in single threaded programs. It looks like some finer grained versions of shared_ptr (like atomic_shared_ptr) arrived recently. I haven't checked into them yet.
  • BenFrantzDale 5y ago
    Typically unique_ptr is represented as a pointer (check sizeof). For shared_ptr, there’s an atomic refcount but no locks. Operations on the shared_ptr object itself aren’t threadsafe (you can’t have the same shared_ptr assigned by two threads at the same time without locking), just like int, but the reference count is atomic, so copies of shared_ptr can safely be shared among threads. Atomic_shared_ptr adds atomicity to the pointer itself. I believe that usually uses locks.