From: Eli Zaretskii <eliz@gnu.org>
To: Antoine Levitt <antoine.levitt@gmail.com>
Cc: lennart.borgman@gmail.com, joakim@verona.se, emacs-devel@gnu.org
Subject: Re: Emacs inotify support?
Date: Sat, 12 Sep 2009 22:45:50 +0300 [thread overview]
Message-ID: <83my50ymj5.fsf@gnu.org> (raw)
In-Reply-To: <6fa54e4e0909121026t797ee747yc2ac395314c3cc40@mail.gmail.com>
> Date: Sat, 12 Sep 2009 19:26:14 +0200
> From: Antoine Levitt <antoine.levitt@gmail.com>
> Cc: lennart.borgman@gmail.com, joakim@verona.se, emacs-devel@gnu.org
>
> > > Date: Sat, 12 Sep 2009 18:36:47 +0200
> > > From: Antoine Levitt <antoine.levitt@gmail.com>
> > > Cc: lennart.borgman@gmail.com, joakim@verona.se, emacs-devel@gnu.org
> > >
> > > If possible, polling should be avoided, though.
> >
> > Why?
>
> Well, I don't know much about file systems, but isn't it always better
> to be notified than to poll ?
But (AFAIU) inotify works by giving the application a file descriptor
that the application needs to pass to `select' or `poll' in order to
get notifications. This is exactly the kind of ``polling'' Emacs does
with any external event (except for signals).
So we are up for polling anyway.
> First, having a notification system
> means it's instantaneous. Second, I'd imagine querying the state of a
> file has a cost (especially if it can't be cached and needs a real
> access to the hard drive). Third, it'd avoid a waste of CPU resources
> (which may be important for power consumption, since, from what I
> understood, the more a program has fixed timers, the more it wakes the
> CPU from sleep). Fourth, being notified is more high-level, since the
> notification itself can be implemented by polling. One could imagine a
> notification API where the backend would use inotify if available,
> polling if not.
You seem to be thinking of some signal-like mechanism. But that's not
how these notifications work (nor do I think it's a good idea for them
to work like that in Emacs, where interrupting code at an arbitrary
moment is not a good idea).
As for wasting CPU time, system calls like `select' and `poll' don't
waste them too much.
next prev parent reply other threads:[~2009-09-12 19:45 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-09-11 20:34 Emacs inotify support? joakim
2009-09-11 21:28 ` Lennart Borgman
2009-09-11 22:54 ` Antoine Levitt
2009-09-11 23:00 ` Lennart Borgman
2009-09-12 13:32 ` Eli Zaretskii
2009-09-12 16:36 ` Antoine Levitt
2009-09-12 16:55 ` Eli Zaretskii
2009-09-12 17:26 ` Antoine Levitt
2009-09-12 19:45 ` Eli Zaretskii [this message]
2009-09-12 20:04 ` Antoine Levitt
2009-09-12 21:24 ` Giuseppe Scrivano
2009-09-13 16:39 ` Richard Stallman
2009-09-13 17:28 ` joakim
2009-09-13 19:42 ` Eli Zaretskii
2009-09-13 22:28 ` Lennart Borgman
2009-09-14 5:47 ` joakim
2009-09-14 18:08 ` Eli Zaretskii
2009-09-12 16:46 ` Richard Stallman
2009-09-13 2:27 ` Miles Bader
2009-09-13 9:33 ` David Kastrup
2009-09-12 16:46 ` Richard Stallman
2009-09-14 7:39 ` Paul R
2009-09-15 7:17 ` Richard Stallman
2009-09-17 15:12 ` Juri Linkov
2009-09-18 9:49 ` Richard Stallman
2009-09-18 12:10 ` David Kastrup
2009-09-18 17:14 ` Stefan Monnier
2009-09-18 18:38 ` joakim
2009-09-21 21:45 ` Dired auto-revert (was: Emacs inotify support?) Juri Linkov
2009-09-21 22:29 ` Drew Adams
2009-09-23 9:05 ` Dired auto-revert Juri Linkov
2009-12-04 0:11 ` Proced revert (Re: Dired auto-revert) Juri Linkov
2009-12-04 2:17 ` Stefan Monnier
2009-12-04 22:21 ` Roland Winkler
2009-12-04 0:09 ` Dired auto-revert Juri Linkov
2009-12-04 2:15 ` Stefan Monnier
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