bug#23002: 25.0.92; sluggish M-x

[YAMAMOTO Mitsuharu]

>>>>> On Tue, 15 Mar 2016 10:21:36 -0400, Stefan Monnier 
>>>>> <monnier@iro.umontreal.ca> said:

>> However, the sluggishness during the evaluation of
>> execute-extended-command--shorter is common to the both ports on OS X,
>> or non-interrupt-driven systems that use polling with SIGALRM for
>> quit/while-no-input handling, in general.  I'm thinkng about applying
>> the following patch to the Mac port, but it might also be useful for
>> other systems.

> Hmm... this seems to indicate that while-no-input is just not really
> working in those systems.

At least, not in a responsive way.  I first tried to shorten the
polling interval in start_polling if Vthrow_on_input is non-nil.  But
let-binding throw-on-input as in the definition of while-no-input was
not enough and we would need some explicit function call to activate
start_polling.

>> +      ;; On non-interrupt-driven systems, while-no-input polls for
>> +      ;; input every `polling-period' (default 2) seconds, and that is
>> +      ;; not frequent enough.  So we call input-pending-p manually.
>> +      (if (and use-polling (input-pending-p))
>> +          (signal 'quit nil))

> Hmm... I'm not sure I understand: if input-pending-p returns non-nil,
> why are we still in this loop?

> IOW, I get the impression that the above call to input-pending-p will
> end up triggering a kind of "poll" to fetch new input, so we should be
> able to arrange for this fetching to trigger whatever should normally be
> triggered by incoming input (e.g. getting out of the while-no-input
> loop), so we could just reduce the above 2 lines to a single call to
> `input-pending-p'.
> I understand this may not seem like a big progress, but "every bit
> counts" ;-) tho more seriously, I'm asking this mostly to better
> understand what's going on (but also because I get the impression that
> (signal 'quit nil) is not always the right thing to do).

Indeed.  (if use-polling (input-pending-p)) does work.

                                     YAMAMOTO Mitsuharu
                                mituharu@math.s.chiba-u.ac.jp