bug#16737: Question about wait_reading_process_output

[Alex Bennée]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Stefan Monnier <monnier@iro.umontreal.ca>
>> Date: Sun, 14 Jun 2015 23:47:42 -0400
>> Cc: emacs-devel <emacs-devel@gnu.org>
>> 
>> > I've been digging into the code trying to get an idea of why bug#16737
>> > fires. My question is where in wait_reading_process_output does it
>> > ensure the various terminal socket reads are run?
>> 
>> I see noone replied yet.  I can't really help you because I don't know
>> this code at all, but I really hope someone else will come along to
>> help,
>
> I will try.
>
> The terminal socket reads are run in gobble_input, which is called
> from detect_input_pending (via a few intermediaries).  Emacs calls
> detect_input_pending when the pselect call in
> wait_reading_process_output finds that some input has arrived, and
> wait_reading_process_output was called with READ_KBD or WAIT_FOR_CELL
> arguments having values that tell it to do so.
>
> Does this answer your question?

Sort of. One thing that's confusing is there are two pselect() calls in
the function:

          if ((pselect (max (max_process_desc, max_input_desc) + 1,
                        &Atemp,
#ifdef NON_BLOCKING_CONNECT
                        (num_pending_connects > 0 ? &Ctemp : NULL),
#else
                        NULL,
#endif
                        NULL, &timeout, NULL)
               <= 0))

and

#if defined (HAVE_NS)
          nfds = ns_select
#elif defined (HAVE_GLIB)
          nfds = xg_select
#else
          nfds = pselect
#endif
            (max (max_process_desc, max_input_desc) + 1,
             &Available,
             (check_write ? &Writeok : 0),
             NULL, &timeout, NULL);

Why the two? Could there be a case where one is triggering handling so
that the second never gets evaluated?

Am I right in thinking all incoming X messages (such as those associated
with cut/paste) will come in via the X terminals gobble_input?

-- 
Alex Bennée