Re: [Tarantool-patches] [PATCH v2] core: handle fiber cancellation for fiber.cond

[Alexander Turenko <alexander.turenko@tarantool.org>]

> > diff --git a/src/lib/core/fiber_cond.c b/src/lib/core/fiber_cond.c
> > index 904a350d9..cc59eaafb 100644
> > --- a/src/lib/core/fiber_cond.c
> > +++ b/src/lib/core/fiber_cond.c
> > @@ -108,6 +108,11 @@ fiber_cond_wait_timeout(struct fiber_cond *c, double timeout)
> >   		diag_set(TimedOut);
> >   		return -1;
> >   	}
> > +	if (fiber_is_cancelled()) {
> > +		if (diag_is_empty(diag_get()))
> > +                        diag_set(FiberIsCancelled);
> 
> I read your argumentation. AFAIU sounds like:"We have a lot of tests
> that check an error in the diag in such case. Also, some user
> applications can check the diag in a similar way. And stack diag can be used
> only in the new versions of tarantool." So, it's true.
> What I propose to think about:
> - this is not simple logic. If a fiber has been cancelled, maybe an error
> will be added to the diag, maybe no - 50/50.
> - this behavior should be documented.
> - ask Mons or Turenko for advice: "What do they think about it?"
> All this up to you.

The fiber_channel implementation (C level) convinced me. It is good to
have the similar behaviour in fiber_cond and fiber_channel.

I would only ask to document this subtle difference in our web
documentation. Python document subtle changes (at least some of them)
and it is nice for users. Example:

Python 2:

 | Popen.send_signal(signal)
 |
 | Sends the signal `signal` to the child.

Python 3:

 | Popen.send_signal(signal)
 |
 | Sends the signal `signal` to the child.
 |
 | Do nothing if the process completed.

(It would be better to mark it with 'Since Python x.y.z', though.)

That is the place, where Python 2 and Python 3 behaviour actually
differs (when the popen implementation aware about a process
termination, i.e. after <popen object>.poll()).

It is important, when you writting a code that must work on both Python
2 and Python 3: you should catch OSError here.