Re: Temporarily disable `timer-event-handler'

[Alexander Shukaev <emacs@Alexander.Shukaev.name>]

On 03/02/2020 16:44, Eli Zaretskii wrote:
> [I removed help-gnu-emacs from the CC list.]
> 
>> From: Stefan Monnier <monnier@iro.umontreal.ca>
>> Date: Mon, 03 Feb 2020 09:01:47 -0500
>> Cc: help-gnu-emacs@gnu.org, emacs-devel@gnu.org
>>
>>> Finally, what's the motivation behind this design?  This looks fragile and
>>> error-prone to run some arbitrary code in the middle of execution of another
>>> code without separating their "stacks" (environment scopes),
>>
>> It's a direct consequence of the implementation, rather than the result
>> of design, AFAICT.
> 
> There's also the need to run a timer as close to its expected time as
> possible, so waiting for any Lisp to return might delay timers too
> much.
> 

Right, the current implementation looks more like coroutines, where 
certain built-in functions yield for timers to run on occasion.  This is 
indeed likely to be more performent and even useful at times, i.e. 
example from Stefan

> But there can also be cases where A does want/need B to be processed
> before A ends.

Nonetheless, given the availability of dynamic binding, I find this 
error-prone.  Is there currently a way in Emacs Lisp to run a function 
within a separate stack, i.e. free of any "user-defined" dynamic 
bindings?  I would imagine that this may be the right solution to fire 
timer events in this manner as it then does not matter whether they run 
in the middle of other routines.

Additionally, I believe the solution to fulfill

> The expectation is that `B' strictly runs after `A' finishes execution.

is also missing.  Some sort of macro (aka `ignore-timers') which 
essentially forbids yielding during the execution of the enclosed body, 
while `let'-binding both `timer-list' and `timer-idle-list' as a naive 
implementation of such does not really scale, since any inner calls to 
`cancel-timer' or otherwise scheduling other (new) timer events would 
have bad side effects.  Otherwise, should be something simple and 
similar to `inhibit-redisplay', aka `inhibit-timers' and 
`inhibit-idle-timers'.