John Torjo wrote:
Ben Hutchings wrote:
expired() may read the count as still being 1 and so return false, but I believe the wnd_shared_ptr constructor will catch the fact that the pointer really has expired. Unfortunately I can't yet see the code to confirm this!
By looking at the code, I would think not. But I may be wrong.
As the comment says, the if( expired() ) test is only an optimization. Remove it if it makes you feel better. ;-) The main idea is that a weak_ptr can never transition by itself from an expired() state back to a !expired() state unless you explicitly assign to it. Because you are in weak_ptr::lock at the moment - a read access - you know that no other threads assign to *this, because this would be a violation of the "basic thread safety" requirements. Therefore, if expired() returns true, it will continue returning true for the foreseeable future, and you can skip the rest of lock().