Re: How do I initialize globalized minor mode only once?

[Dmitry Gutov <dgutov@yandex.ru>]

Barry Margolin <barmar@alum.mit.edu> writes:

> In article <mailman.4534.1341975266.855.help-gnu-emacs@gnu.org>,
>  Dmitry Gutov <dgutov@yandex.ru> wrote:
>
>> Hi all,
>> 
>> I have written a globalized minor mode which has a relatively costly
>> initialization (external process call), which I need to do when the mode
>> is enabled.
>> 
>> But the turn-on function is getting called twice for each new opened
>> buffer, once in default major mode, and once in the final major mode.
>> 
>> What's the best way to turn on the minor mode only once?
>> Currently I'm comparing major-mode value to the default value, but
>> that's probably not the best solution, since the minor mode in question
>> can apply to some fundamental-mode (or other default mode) buffers, too.
>
> Why not just set a variable saying whether you've done the 
> initialization:
>
> (defvar *my-mode-initialized* nil)
> ...
>
>   (if (not *my-mode-initialized*)
>       (progn
>         ... 
>         (setq *my-mode-initialized* t)))

My first reaction was "because major mode change kills all local variables",
but that's not exactly true - with enough sprinkling of 'permanent-local
and 'permanent-local-hook properties, this might work.

But what if the user tries to turn off and on the minor mode, or the
global mode, or both? I'd want the initialization performed in these
cases. When or where would I set the variable to nil?