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Date: Wed, 14 Feb 2001 11:08:38 +0300
From: Egor Duda <deo AT logos-m DOT ru>
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To: cygwin AT cygwin DOT com
Subject: Re: Optimizing away "ReadFile" calls when Make calls stat()
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Hi!

Tuesday, 13 February, 2001 Christopher Faylor cgf AT redhat DOT com wrote:

CF> On Tue, Feb 13, 2001 at 02:54:01PM -0500, DJ Delorie wrote:
>>> But it does nothing at all for the "usual case" I'm trying to
>>> optimize, which is Make stat()ing a file but never reading it.
>>
>>It does, because stat() reads the file twice, once to see if it's a
>>symlink, and once to see if the executable bit needs to be set.

CF> If it is actually doing this, then that's a bug.  I went to some effort
CF> a year or so ago to do away with the second read.

not  meaning to be too pushy ;), but i'd like to bring the thread

http://sources.redhat.com/ml/cygwin-developers/2000-03/msg00077.html

back to life. I have to say, that not only ReadFile() is slowing things
up,  but  CreateFile()  too.  i tend to think that cygwin- (or win32-)
specific  parts  in  ported  applications  are  unavoidable  evil (and
"make"   sources   are   already   full   of them).

quick  grep  through "make"  sources  reveals  that  we  need  st_mode
only to check in for S_ISREG(m)  or  S_ISDIR(m). So application porter
can  use  this  info to give  stat a hint, and stat won't need to read
file, and even open it. 

giving  porter  a single universal tool to be more specific about what
he  wants  to  get from stat() has one more benefit. otherwise, porter
will  tend  to use different native win32 calls such as GetFileTime(),
GetFileAttributes(),  GetFileSize()  etc.  which are harder to find in
large  source  tree  when needed. with stat_lite he had just to do the
simple grep.

the  only problem with this approach i can see is that if we introduce
new  API  and applications start to use it we became "bound" to it and
it'll  be  not too easy to deprecate ad remove it afterwards. OTOH, we
can  always  make stat_lite() a simple wrapper to stat() if the latter
become fast enough.

i'm ready to submit an appropriate patch against current sources.

Egor.            mailto:deo AT logos-m DOT ru ICQ 5165414 FidoNet 2:5020/496.19



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