weak_ptr::lock() thread safety

[Gennady Proskurin <gpr@…>]

Imagine the following code:

shared_ptr<T> sp(new ...);
weak_ptr<T> wp(sp);

sp.reset(); // thread A
shared_ptr<T> sp1 = wp.lock(); // thread B

It is not clear from documentation, whether it is safe to call shared_ptr::reset() and weak_ptr::lock() concurrently in different threads. It is very frequently asked question and should be documented explicitly.