Subject: Re: bug#33839: 26.1.90; Emacs occasionally fails to receive asynchronous subprocess output in batch mode

From: Eli Zaretskii <[email-masked]>
Date: Sun, 23 Dec 2018 18:54:15 +0200

> From: Philipp Stephani <[email-masked]>
> Date: Sun, 23 Dec 2018 17:45:31 +0100
> Cc: [email-masked]
> 
> Am So., 23. Dez. 2018 um 16:22 Uhr schrieb Eli Zaretskii <[email-masked]>:
> >
> > > From: Philipp <[email-masked]>
> > > Date: Sun, 23 Dec 2018 03:28:53 +0100
> > >
> > > (with-temp-buffer
> > >   (let ((proc (make-process :name "test"
> > >                             :command '("bash" "-c" "echo stdout; echo stderr >&2")
> > >                             :buffer (current-buffer)
> > >                             :connection-type 'pipe
> > >                             :sentinel #'ignore
> > >                             :noquery t
> > >                             :coding '(utf-8-unix . utf-8-unix))))
> > >     (when (process-live-p proc)
> > >       (process-send-eof proc))
> > >     (while (process-live-p proc)
> > >       (accept-process-output proc))
> > >     (cl-assert (equal (buffer-string) "stdout\nstderr\n") :show-args)))
> > >
> > > Then evaluate this form repeatedly.  Occasionally the buffer is empty
> > > and the assertion triggers.
> >
> > Isn't there an inherent race condition here?
> 
> Maybe? If so, then it should be documented, with an explanation how to
> write this in a race-free manner.

Can you tell why you used the process-live-p condition for calling
accept-process-output?  What happens if you do that unconditionally?