* Why doesn't Emacs have an `active-timer-p' command, or why can't I find it?
@ 2021-11-11 20:31 Alan Mackenzie
2021-11-11 20:37 ` Eli Zaretskii
0 siblings, 1 reply; 8+ messages in thread
From: Alan Mackenzie @ 2021-11-11 20:31 UTC (permalink / raw)
To: emacs-devel
Hello, Emacs.
There doesn't appear to be an easy way in a Lisp program to determine if
a timer object is active. Something like (active-timer-p TIMER), or
even (timerp TIMER t), where the t is an &optional argument meaning
"active" (a bit like the LIVE parameter in minibufferp).
Does such a function really not exist, or have I somehow not managed to
find it?
If it doesn't exist, what is the reason? The command timer-list clearly
manages to know this. The usefulness of active-timer-p is surely
obvious. (Well, it is to me, at least.)
At the very least, there could be a section in the Elisp manual
documenting why the function doesn't exist.
--
Alan Mackenzie (Nuremberg, Germany).
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: Why doesn't Emacs have an `active-timer-p' command, or why can't I find it?
2021-11-11 20:31 Why doesn't Emacs have an `active-timer-p' command, or why can't I find it? Alan Mackenzie
@ 2021-11-11 20:37 ` Eli Zaretskii
2021-11-11 21:08 ` Alan Mackenzie
0 siblings, 1 reply; 8+ messages in thread
From: Eli Zaretskii @ 2021-11-11 20:37 UTC (permalink / raw)
To: Alan Mackenzie; +Cc: emacs-devel
> Date: Thu, 11 Nov 2021 20:31:24 +0000
> From: Alan Mackenzie <acm@muc.de>
>
> There doesn't appear to be an easy way in a Lisp program to determine if
> a timer object is active.
What is an "active timer", and how does it differ from a non-active
one?
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: Why doesn't Emacs have an `active-timer-p' command, or why can't I find it?
2021-11-11 20:37 ` Eli Zaretskii
@ 2021-11-11 21:08 ` Alan Mackenzie
2021-11-11 21:24 ` Óscar Fuentes
0 siblings, 1 reply; 8+ messages in thread
From: Alan Mackenzie @ 2021-11-11 21:08 UTC (permalink / raw)
To: Eli Zaretskii; +Cc: emacs-devel
Hello, Eli.
On Thu, Nov 11, 2021 at 22:37:43 +0200, Eli Zaretskii wrote:
> > Date: Thu, 11 Nov 2021 20:31:24 +0000
> > From: Alan Mackenzie <acm@muc.de>
> > There doesn't appear to be an easy way in a Lisp program to determine if
> > a timer object is active.
> What is an "active timer", and how does it differ from a non-active
> one?
An active timer is one which will trigger its timer function at the
appropriate time.
A non-active timer is one which will not trigger any timer function -
for example, a non-repeating timer which has already triggered.
timerp returns t for both of these objects.
--
Alan Mackenzie (Nuremberg, Germany).
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: Why doesn't Emacs have an `active-timer-p' command, or why can't I find it?
2021-11-11 21:08 ` Alan Mackenzie
@ 2021-11-11 21:24 ` Óscar Fuentes
2021-11-12 2:49 ` Lars Ingebrigtsen
0 siblings, 1 reply; 8+ messages in thread
From: Óscar Fuentes @ 2021-11-11 21:24 UTC (permalink / raw)
To: emacs-devel
Alan Mackenzie <acm@muc.de> writes:
> Hello, Eli.
>
> On Thu, Nov 11, 2021 at 22:37:43 +0200, Eli Zaretskii wrote:
>> > Date: Thu, 11 Nov 2021 20:31:24 +0000
>> > From: Alan Mackenzie <acm@muc.de>
>
>> > There doesn't appear to be an easy way in a Lisp program to determine if
>> > a timer object is active.
>
>> What is an "active timer", and how does it differ from a non-active
>> one?
>
> An active timer is one which will trigger its timer function at the
> appropriate time.
>
> A non-active timer is one which will not trigger any timer function -
> for example, a non-repeating timer which has already triggered.
>
> timerp returns t for both of these objects.
Following the implicit definition on the docstring of `cancel-timer', an
active timer is a timer object contained in the list of active timers
(actually, either in `timer-list' or in `timer-idle-list'.)
An implementation would be
(defun timer-active-p (timer)
(timer--check timer)
(or (memq timer timer-list))
(memq timer timer-idle-list))
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: Why doesn't Emacs have an `active-timer-p' command, or why can't I find it?
2021-11-11 21:24 ` Óscar Fuentes
@ 2021-11-12 2:49 ` Lars Ingebrigtsen
2021-11-12 7:55 ` ๊Unsubscribe Sakesun Roykiattisak
2021-11-12 13:13 ` Why doesn't Emacs have an `active-timer-p' command, or why can't I find it? Rudolf Schlatte
0 siblings, 2 replies; 8+ messages in thread
From: Lars Ingebrigtsen @ 2021-11-12 2:49 UTC (permalink / raw)
To: Óscar Fuentes; +Cc: emacs-devel
Óscar Fuentes <ofv@wanadoo.es> writes:
> An implementation would be
>
> (defun timer-active-p (timer)
> (timer--check timer)
> (or (memq timer timer-list))
> (memq timer timer-idle-list))
Sounds useful to me.
--
(domestic pets only, the antidote for overdose, milk.)
bloggy blog: http://lars.ingebrigtsen.no
^ permalink raw reply [flat|nested] 8+ messages in thread
* ๊Unsubscribe
2021-11-12 2:49 ` Lars Ingebrigtsen
@ 2021-11-12 7:55 ` Sakesun Roykiattisak
2021-11-12 13:13 ` Why doesn't Emacs have an `active-timer-p' command, or why can't I find it? Rudolf Schlatte
1 sibling, 0 replies; 8+ messages in thread
From: Sakesun Roykiattisak @ 2021-11-12 7:55 UTC (permalink / raw)
To: emacs-devel
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^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: Why doesn't Emacs have an `active-timer-p' command, or why can't I find it?
2021-11-12 2:49 ` Lars Ingebrigtsen
2021-11-12 7:55 ` ๊Unsubscribe Sakesun Roykiattisak
@ 2021-11-12 13:13 ` Rudolf Schlatte
2021-11-12 14:12 ` Filipp Gunbin
1 sibling, 1 reply; 8+ messages in thread
From: Rudolf Schlatte @ 2021-11-12 13:13 UTC (permalink / raw)
To: emacs-devel
Lars Ingebrigtsen <larsi@gnus.org> writes:
> Óscar Fuentes <ofv@wanadoo.es> writes:
>
>> An implementation would be
>>
>> (defun timer-active-p (timer)
>> (timer--check timer)
>> (or (memq timer timer-list))
>> (memq timer timer-idle-list))
>
> Sounds useful to me.
Of course, the form
(when (timer-active-p my-timer)
(do-something-that-errors-when-timer-inactive my-timer))
can still throw an error, since the return value of `timer-active-p' is
outdated as soon as the function returns.. (Or can timers only fire
when Emacs is otherwise idle?)
Rudi
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: Why doesn't Emacs have an `active-timer-p' command, or why can't I find it?
2021-11-12 13:13 ` Why doesn't Emacs have an `active-timer-p' command, or why can't I find it? Rudolf Schlatte
@ 2021-11-12 14:12 ` Filipp Gunbin
0 siblings, 0 replies; 8+ messages in thread
From: Filipp Gunbin @ 2021-11-12 14:12 UTC (permalink / raw)
To: Rudolf Schlatte; +Cc: emacs-devel
On 12/11/2021 14:13 +0100, Rudolf Schlatte wrote:
> Lars Ingebrigtsen <larsi@gnus.org> writes:
>
>> Óscar Fuentes <ofv@wanadoo.es> writes:
>>
>>> An implementation would be
>>>
>>> (defun timer-active-p (timer)
>>> (timer--check timer)
>>> (or (memq timer timer-list))
>>> (memq timer timer-idle-list))
>>
>> Sounds useful to me.
>
> Of course, the form
>
> (when (timer-active-p my-timer)
> (do-something-that-errors-when-timer-inactive my-timer))
>
> can still throw an error, since the return value of `timer-active-p' is
> outdated as soon as the function returns.. (Or can timers only fire
> when Emacs is otherwise idle?)
From (elisp) Timers:
--8<---------------cut here---------------start------------->8---
Emacs cannot run timers at any arbitrary point in a Lisp program; it
can run them only when Emacs could accept output from a subprocess:
namely, while waiting or inside certain primitive functions such as
‘sit-for’ or ‘read-event’ which _can_ wait. Therefore, a timer’s
execution may be delayed if Emacs is busy. However, the time of
execution is very precise if Emacs is idle.
--8<---------------cut here---------------end--------------->8---
So it depends on what do-something-that-errors-when-timer-inactive does.
^ permalink raw reply [flat|nested] 8+ messages in thread
end of thread, other threads:[~2021-11-12 14:12 UTC | newest]
Thread overview: 8+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2021-11-11 20:31 Why doesn't Emacs have an `active-timer-p' command, or why can't I find it? Alan Mackenzie
2021-11-11 20:37 ` Eli Zaretskii
2021-11-11 21:08 ` Alan Mackenzie
2021-11-11 21:24 ` Óscar Fuentes
2021-11-12 2:49 ` Lars Ingebrigtsen
2021-11-12 7:55 ` ๊Unsubscribe Sakesun Roykiattisak
2021-11-12 13:13 ` Why doesn't Emacs have an `active-timer-p' command, or why can't I find it? Rudolf Schlatte
2021-11-12 14:12 ` Filipp Gunbin
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