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Re: substantial 'glob' speedup ...

From: Michael Meeks
Subject: Re: substantial 'glob' speedup ...
Date: Fri, 08 Apr 2011 17:08:31 +0100

Hi Paul,

On Thu, 2011-04-07 at 08:53 -0400, Paul Smith wrote:
> That's interesting.  I wonder why the glob expansion is so inefficient;

        Oh - because it is also testing for existence :-) and also doing a
chunk of dynamic memory management with it I suspect.

> I would expect it to do the same kinds of checks that you're doing (that
> is, basically be a string-walk unless a glob character is found).

> Why not just use strpbrk()?

        I had no idea it existed ? :-) it would be preferable of course. I
tried a somewhat differet approach (patch appended).

        before      orig. patch GLOB_NOMAGIC
real    0m5.795s    0m2.634s    0m3.569s
user    0m3.513s    0m2.526s    0m3.450s
sys     0m2.274s    0m0.101s    0m0.113s

        But but apparently the malloc / free overhead from our 700k 'glob'
calls burns rather a lot of extra CPU here, the patch is slightly
simpler (though hardly if you use strpbrk).

        So - I'd rather prefer my original; with the glob scope indented to
avoid the glob_free having an ugly condition, and using strpbrk; but
that's just me.

        HTH !


diff --git a/read.c b/read.c
index a3ad88e..81ca7cd 100644
--- a/read.c
+++ b/read.c
@@ -2904,6 +2904,7 @@ parse_file_seq (char **stringp, unsigned int size, int 
       const char *name;
       const char **nlist = 0;
       char *tildep = 0;
+      int glob_flags;
 #ifndef NO_ARCHIVES
       char *arname = 0;
       char *memname = 0;
@@ -3112,7 +3113,10 @@ parse_file_seq (char **stringp, unsigned int size, int 
 #endif /* !NO_ARCHIVES */
-      switch (glob (name, GLOB_NOSORT|GLOB_ALTDIRFUNC, NULL, &gl))
+      glob_flags = GLOB_NOSORT|GLOB_ALTDIRFUNC;
+      if (!(flags & PARSEFS_EXISTS))
+       glob_flags |= GLOB_NOMAGIC;
+      switch (glob (name, glob_flags, NULL, &gl))
        case GLOB_NOSPACE:
          fatal (NILF, _("virtual memory exhausted"));

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