[sorry if you're getting this twice Stefan, i forgot to cc everyone else]

On Thu, Oct 5, 2017 at 2:11 PM, Stefan Monnier <monnier@iro.umontreal.ca>
wrote:
>
> >> :sentinel
> >> (lambda (p _ev)

> > way to do this is to check if 'p' is 'eq' to the buffer-local value of
> > clang-flymake--procress.
>
> While I agree that it should check whether `p` is obsolete (just in case
> something went wrong elsewhere), `p` should have been killed when the
> other process was launched,

I believe the code examples presented here already do that:

>> (when (process-live-p gcc--flymake-proc)
>>    (kill-process gcc--flymake-proc))

> so this sentinel should only be called with an obsolete `p` in response
to such a kill.

But while a "killed" 'p' is obsolete, the reverse isn't true. When lauching
B, the
process A might have already have exited cleanly. Hence A it is not live
anymore, and can't be killed. But A's sentinel might not have had a chance
to run yet. When it does run, A's sentinel must notice that it is obsolete
by
some means, and checking for eqness seems the easiest (in flymake-proc.el
I set an 'obsolete' property in the proc).

> BTW, it should also check `ev` in case the event is just that someone
> suspended/resumed the background process.

That is true.

We should come up with a canonic way to launch flymake processes
and then either hide that behind an abstraction or document it.

João