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Re: Strange performance hit for insert-file-contents-literally()

From: Nordlöw
Subject: Re: Strange performance hit for insert-file-contents-literally()
Date: Fri, 27 Nov 2009 00:26:53 -0800 (PST)
User-agent: G2/1.0

On Nov 27, 8:58 am, Nordlöw <address@hidden> wrote:
> I am implementing a package for doing recursive file system magic-
> detect and scan/search/grep for pattern.
> In this process I have stumbled across a strange performance problem;
> If I want to grep for raw binary (literal) patterns, I thought that
>   (benchmark-run 1 (with-temp-buffer (buffer-disable-undo) (insert-
> file-contents-literally "~/pnw.tar.gz" nil)))
> would given optimal performance but it turns out that
>   (benchmark-run 1 (save-excursion (set-buffer (find-file-noselect "~/
> pnw.tar.gz" t t))))
> is about 11 times faster on my laptop PC (the first time its called of
> course, the second time it reuses the open buffer so that doesn't
> count)!.
> As find-file-noselect() uses insert-file-contents-literally() it must
> disable some stuff that find-file-literally() doesn't. The question is
> what?
> I would prefer no to be forced to use find-file-noselect() as this
> does other unneccessary stuff I don't need.
> It also reuses the buffer if its already open which is not always what
> I want with compressed files for example.
> My logic namely detects the file magic headers for compressed files
> and then reopens them non-literally using jka-compr in order to detect
> their underlying (decompressed) type like the unix program "file"
> does.
> Is this maybe a bug?
> I am currently using Emacs CVS.
> Thanks in advance for all tips,
> Nordlöw

I also need the sub-file aspect (BEG END) of  insert-file-contents-

I could get by with
- find-file-noselect() when I want to scan the whole file a la grep
- insert-file-contents-literally() when I only want to open a part
(typically beginning or end) when I want to detect its contents/type a
al file.

How can I detect if a file is already opened before calling find-file-
noselect() on it?
Reason: I don't want files that don't match my grep pattern to remain
opened (kill its buffer).

Please help! This package I am writing will soon be release to the
public (EmacsWIki) and will be really useful!
It is an elegant (I think) merge of the UNIX command line tools find,
tree, file, grep and file all implemented in pure emacs lisp (making
it independent of underlying OS read it will work on windows) with its
own nice colored presentation/hit-navigation mode. It is compatible
with TRAMP and does auto-compression (jka) of files that are being
searched and supports emacs-style regexps (of course) making it simply
the ultimate file system scanning tool for Emacs users.


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