request_stop() return value is invalid

[Vlad]

request_stop() method in stop_source should return

true if the stop_source object has a stop-state and this invocation made a stop request, otherwise false.

But your method returns false in case of successful request for the invocation.

The same logic I see in the NVIDIA project

P.S. Also why did you skip unlock()? Is it really safe for 2 threads that make the stop_request ?