Re: making software with Emacs and Elisp

[Pascal J. Bourguignon]

Emanuel Berg <embe8573@student.uu.se> writes:

> "Pascal J. Bourguignon" <pjb@informatimago.com> writes:
>
>> emacs does manage memory, or schedule processor time
>> for the various functions running in emacs.
>
> So it does? Then it *is* an OS within the OS, at the
> very least, like a Chinese box or those Russian
> dolls. 

Indeed.


> But - when does this happen? 
> And how is it done?


> For example, if I write an interactive defun, I always
> thought that was executed sequentially upon
> invocation. Is that so?  And, how do I code a defun that
> is interactive in the sense it can be invoked by the
> user, but "batch" in the sense that it is run in the
> background, perhaps as an infinite loop? And if I make
> two such defuns, can I give them different priorities,
> and otherwise like the PCBs of a "real" OS, to setup how
> they should relate to everything else?

If you want to run processes in the outer system you can call
start-process amongst a few other functions.


But you can have code scheduled to run in emacs.  It is not a preemptive
system, but a collaborative one, where each task must release the CPU
quickly enough for the rest of the system to stay responsive.  But a lot
of tasks are scheduled this way in emacs (eg. background font-locking,
semantic incremental parses, etc). See: run-with-idle-timer


Things like priorities or "how things relate to everything else" are
notions specific to a given system.  Eg. emacs run-with-idle-timer
doesn't deal with priorities, only with timing. 


>> Also, "Operating System" doesn't mean unix-like
>> architecture.  You can have very different
>> architectures.
>
> Yeah, I guess that's just a schoolbook issue anyway.
>
>> $ emacs -Q --batch -l myprogram.el
>> ...
>>     $ cat myprogram
>>     #!/bin/sh
>>     exec emacs -Q --batch -l myprogram.el
>
> Great!

-- 
__Pascal Bourguignon__
http://www.informatimago.com/