Re: Why doesn't Emacs have an `active-timer-p' command, or why can't I find it?

[Óscar Fuentes]

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))