[MIT-Scheme-devel] Edwin slow file save over WebDAV

[Richard Loveland]

On Tuesday, December 11, 2012, Taylor R Campbell  wrote:
> Whoops, looks like I neglected to answer this last month.
>
>
>    Date: Thu, 1 Nov 2012 10:05:13 -0400
>    From: Richard Loveland <address@hidden>
>
>    My layman's interpretation is:
>
>    1. write the file (quick)
>    2. do something called `thread_selfid' (slow)
>    3. stat the `Invoice Service.txt' file (quick, it exists)
>    4. stat the `.git' directory, which does not exist (slow)
>
>    The dtruss output is littered with these stat calls to non-existent
>    version control directories -- I'm guessing they just correspond to
>    `file-exists?' type procedures?
>
> Sounds about right: vc is trying to detect whether you're using any
> revision control system by statting the revision control files and
> directories.  Unfortunately, at the moment, there's no good way to
> turn this off...  Perhaps we ought to have a variable controlling
> whether vc autodetection happens, which VC-HOOK:FIND-FILE would check,
> or something like that.

I've created a patch (attached) that solves this issue for me. Rather than turn off VC-HOOK:FIND-FILE, I've enabled a quicker check in VC-HOOK:AFTER-SAVE of whether a buffer has the 'VC-MASTER property when the file is saved. The previous version of VC-HOOK:AFTER-SAVE was calling the same procedure (BUFFER-VC-MASTER) as VC-HOOK:FIND-FILE. Unfortunately, BUFFER-VC-MASTER calls several nested procedures, each of which perform loops. I suspect that this heavy checking is worthwhile when opening a file, since the buffer's 'VC-MASTER property doesn't exist yet, but seems unnecessary in the VC-HOOK:AFTER-SAVE case (since VC-HOOK:FIND-FILE should already have run and set 'VC-MASTER).

This results in a speedup of factor 5 or so when saving files mounted via WebDAV (~30 seconds down to ~6). Now Edwin's performance is directly on par with GNU Emacs when saving these files on my system.

Please let me know if this patch is acceptable. If so I'm happy to sign papers, etc. as needed.

vc.patch
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