Race condition in set_state

[alexstanovoy]

Code link

Let's imagine we have not only Active and Paused states, but also some valid Active2 state. Steps to reproduce:

1. self.current_state() returns Active for the first thread.
2. self.current_state() returns Active for the second thread.
3. The first thread changes the state to Paused according to the match.
4. The second thread changes the state to Active2 according to the match.

Without the Active2 state, it's currently impossible to reproduce. But it could be a problem when the new state appears.

[LizardWizzard]

Related WIP PR: #2665. TLDR: we can use send_if_modified to perform the match under watchs internal RWLock

[hlinnaka]

Is this the same as #2003 ?

[koivunej]

Noted that this issue no longer points to any sensible location in code. The Sender::send_modify is now being used through out per earlier comment #2727 (comment).

[hlinnaka]

The code has changed a lot since this issue was created. Closing.