Re: request: make-frame-visible hook

[Kim F. Storm]

Miles Bader <address@hidden> writes:

> Lynbech Christian <address@hidden> writes:
>> Alternatively you can consider using post-command-hook, this is run all
>> the time and this particular problem should not pose a performance
>> problem.
>
> Using post-command-hook _will_ pose a performance problem if everybody
> and their dog gets in the habit of using it... 

I know people are repeating this claim again and again as "gospel truth".

However, I strongly doubt this is really true in practice.
The amount of lisp code executed in the post-command-hook is not nearly
comparable to the amount of work done in redisplay for every (non-trivial)
keypress...  

E.g. just hitting RET performs - I would guess - 1000 times the code anybody
has every put into the post-command-hook...

IMO, the real problem using post-command-hook is that there is no way to
control the sequence of things that is done via that hook - so if you have
two packages putting stuff on the hook - and they both do something which
modifies either buffer contents or visual appearence - then users may see
different results depending on which package is loaded first.

So I agree that using post-command-hook is not a good thing
.. unfortunately there are not many hooks in Emacs which can do global
things - and there seem to be a reluctance to adding "necessary" hooks
(in the sense that the alternative is to use post-commmand-hook).

E.g. where is:
 before-modify-buffer-hook  (run before changing buffer)
 after-modify-buffer-hook  (run after changing buffer)
 before-cursor-move-hook
 after-cursor-move-hook
 before-window-buffer-change-hook
 after-window-buffer-change-hook
 focus-window-hook
 unfocus-window-hook
 enter-buffer-hook
 exit-buffer-hook
etc. etc. etc.

I'm not going to discuss semantics of those hooks here, but these things
are typically used for stuff that would currently involve pre-command-hook and
post-command-hook code to notice and react to specific state changes.

-- 
Kim F. Storm <address@hidden> http://www.cua.dk