GNU bug report logs - #17328
dfa.c will fail if used on more than one DFA

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Aharon Robbins <arnold <at> skeeve.com>
Subject: bug#17328: closed (Re: bug#17328: dfa.c will fail if used on more
 than one DFA)
Date: Wed, 23 Apr 2014 19:50:04 +0000

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Your bug report

#17328: dfa.c will fail if used on more than one DFA

which was filed against the grep package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 17328 <at> debbugs.gnu.org.

-- 
17328: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=17328
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Aharon Robbins <arnold <at> skeeve.com>, 17328-done <at> debbugs.gnu.org
Subject: Re: bug#17328: dfa.c will fail if used on more than one DFA
Date: Wed, 23 Apr 2014 12:49:29 -0700

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Thanks for reporting that.  That static variable was the result of a 
recent optimization.  I guess we'll need to optimize in a different 
way.  I noticed another static variable that dfaexec also uses, namely 
'mbs'; this needs to be moved into the struct dfa, for the benefit of 
any applications that really need stateful encodings.  A bonus is that I 
expect this'll make the dfa code run a bit faster. I installed the 
attached patch, which I hope addresses the issues you raised along with 
the mbs issue.

The code still needs more work in this area.  There shouldn't be any 
static variables at all, even when parsing, though this would change the 
API.  And the code isn't consistent about referring to dfa->mb_cur_max 
versus MB_CUR_MAX; not sure why that is.

[0001-dfa-omit-static-variables-that-limited-dfaexec-to-on.patch (text/x-patch, attachment)]

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From: Aharon Robbins <arnold <at> skeeve.com>
To: bug-grep <at> gnu.org
Subject: dfa.c will fail if used on more than one DFA
Date: Wed, 23 Apr 2014 21:36:11 +0300

Hello.

There is a built-in assumption that the routines in dfa.c will only
be used on one struct dfa.  This is true for grep but not true for gawk.
I found this when trying to update gawk's dfa with all the changes that
have been coming through.  The patch is below.

Thanks,

Arnold
-----------------------
diff --git a/src/dfa.c b/src/dfa.c
index 65fc03d..85ab9bd 100644
--- a/src/dfa.c
+++ b/src/dfa.c
@@ -3244,15 +3244,10 @@ dfaexec (struct dfa *d, char const *begin, char *end,
 
   if (d->mb_cur_max > 1)
     {
-      static bool mb_alloc = false;
       memset (&mbs, 0, sizeof (mbstate_t));
-      if (!mb_alloc)
-        {
-          d->mb_match_lens = xnmalloc (d->nleaves, sizeof *d->mb_match_lens);
-          d->mb_follows = xmalloc (sizeof *d->mb_follows);
-          alloc_position_set (d->mb_follows, d->nleaves);
-          mb_alloc = true;
-        }
+      d->mb_match_lens = xnmalloc (d->nleaves, sizeof *d->mb_match_lens);
+      d->mb_follows = xmalloc (sizeof *d->mb_follows);
+      alloc_position_set (d->mb_follows, d->nleaves);
     }
 
   for (;;)
@@ -3434,8 +3429,13 @@ free_mbdata (struct dfa *d)
     {
       free (d->mb_follows->elems);
       free (d->mb_follows);
+      d->mb_follows = NULL;
+    }
+  if (d->mb_match_lens)
+    {
+      free (d->mb_match_lens);
+      d->mb_match_lens = NULL;
     }
-  free (d->mb_match_lens);
 }
 
 /* Initialize the components of a dfa that the other routines don't

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