Re: What do 'hooks' do and how do they do it?

[Dirk-Jan C. Binnema <djcb.bulk@gmail.com>]

Hi Bill,

>>>>> "Bill" == William Case <billlinux@rogers.com> writes:

    Bill> Hi;
    Bill> This is not an urgent question, it is more in the way of a request for
    Bill> an explanation by anyone who has the time and inclination to do a little
    Bill> teaching.

    Bill> I know at a high level what a 'hook' is and how to use it an elisp
    Bill> statement.  And, I have seen hooks used in other programs like SELinux.

    Bill> But I am curious about what is going on at the kernel level with a
    Bill> 'hook'.  If someone can give me a brief overview in relatively plain
    Bill> language, I would appreciate it.

    Bill> e.g. some of the kind of questions that spring to mind.
    Bill> Is it a process that is added to the task structure waiting to be
    Bill> called?
    Bill> How is it woken up?  And what kind of events might wake it?  etc.

I think Drew Adams gave a very clear answer about the Emacs implementation,
but let me add that the concept of a 'hook' is simply a programming technique:
the ability to set some function to be run whenever a particular event
happens.

The concept is in use in many places (such as SE-Linux), but how it's
implemented is quite different. In Emacs-Lisp, the hooks are simply Lisp
functions to be called -- no kernel involved (well...).

See: http://en.wikipedia.org/wiki/Hooking

Best wishes,
Dirk.

-- 
Dirk-Jan C. Binnema                  Helsinki, Finland
e:djcb@djcbsoftware.nl           w:www.djcbsoftware.nl
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