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Date:	Tue, 13 Feb 2001 14:22:21 -0500
To:	jik-cygwin AT curl DOT com
From:	"Larry Hall (RFK Partners, Inc)" <lhall AT rfk DOT com>
Subject:	Re: Optimizing away "ReadFile" calls when Make calls stat()
Cc:	cygwin AT cygwin DOT com
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At 02:17 PM 2/13/2001, jik-cygwin AT curl DOT com wrote:
> >  Date: Tue, 13 Feb 2001 14:08:58 -0500
> >  From: "Larry Hall (RFK Partners, Inc)" <lhall AT rfk DOT com>
> >  
> >  >1) The cache would have to be automatically invalidated whenever the
> >  >    file is changed, and you'd thus need to check if a file has changed
> >  >    before using the cache, and those checks would themselves take
> >  >    time.
> >  
> >  I'd submit that while this may be true in general, it shouldn't be in the
> >  case of symbolic links and executables.  These attributes don't really change
> >  or, if they do, they change in a very defined way which should make it 
> >  possible to track.
>
>Yikes, I don't agree with that at all.
>
>Non-deterministic behavior is *much* worse than slow behavior.  It
>would be *impossible* for Cygwin to track every single change to
>symbolic links and/or executable files, since people can modify such
>files without going through Cygwin at all (e.g., modifying them
>directly with a Windows app, or modifying such a file on a SAMBA mount
>through Linux).
>
>Since it's impossible for Cygwin to know when such files are changed
>out from under it, it *must* check them, or at least check if they
>have been changed, each time they are accessed.


Again, in general, I agree with you.  Still, it depends on what attributes
are being cached.  If we limit ourselves to checking for executables and
symbolic links, I don't see a major problem.  The only thing that this won't 
catch is places which someone changes their executable file to a 
non-executable or vice versa (same for symbolic link files).  Assuming the 
cache ages relatively quickly, this shouldn't be an issue.  Your point is
taken however.



Larry Hall                              lhall AT rfk DOT com
RFK Partners, Inc.                      http://www.rfk.com
118 Washington Street                   (508) 893-9779 - RFK Office
Holliston, MA 01746                     (508) 893-9889 - FAX



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