Finding weak_ptrs referring to a shared_ptr

Is there a way to find out the number of weak_ptrs a shared_ptr is being referred by?

unique()/use_count() could be used for finding the shared_ptrs but is there a similar construct for finding the referring weak_ptrs.

I want to release the resource held by the shared_ptr only if there are no weak_ptrs referring to it. So that sometime in future if I try creating a shared_ptr from this weak_ptr, I shouldn't end up with a nullptr.

Is this possible currently in C++11?