Re: [perl #59516] Memory leak with regex in 5.10.0

[Marcus Holland-Moritz <mhx-perl@gmx.net>]

On 2008-10-04, at 15:02:32 +0100, Dave Mitchell wrote:

> On Sat, Oct 04, 2008 at 02:51:09PM +0100, Nicholas Clark wrote:
> > On Sat, Oct 04, 2008 at 12:55:04PM +0100, Dave Mitchell wrote:
> > 
> > > The leak appears to be somewhere in the compilation of character classes.
> > > The following code leaks like a sieve on 5.10.0 and bleed, but not 5.8.8:
> > > 
> > >     while (1) {
> > > 	qr/[a]/;
> > >     }
> > 
> > Are you sure that it's character classes?
> > 
> > ./perl -le 'while (1) { qr// }'
> > 
> > merrily chews through memory like it's going out of fashion. However, all
> > memory is freed at the end of the program:
> 
> Hmm, maybe I reduced the original code too much, and threw out the
> original bug but gained a new one.
> 
> 
> This doesn't leak:
> 
>     my $n = 1;
>     while (1) {
> 	$n = 1 - $n;
> 	"abc" =~ /$n/;
>     }
> 
> This does:
> 
>     my $n = 1;
>     while (1) {
> 	$n = 1 - $n;
> 	"abc" =~ /[a]${n}/;
>     }
> 
> (The non-constant $n is to defeat regex compilation caching).

Fixed with the following change:

Change 34507 by mhx@mhx-r2d2 on 2008/10/18 18:11:57

	Fix memory leak in // caused by single-char character class
	optimization. This was most probably introduced with #28262.
	This change fixes perl #59516.

Affected files ...

... //depot/perl/regcomp.c#660 edit

Differences ...

==== //depot/perl/regcomp.c#660 (text) ====

@@ -8350,6 +8350,9 @@
         *STRING(ret)= (char)value;
         STR_LEN(ret)= 1;
         RExC_emit += STR_SZ(1);
+	if (listsv) {
+	    SvREFCNT_dec(listsv);
+	}
         return ret;
     }
     /* optimize case-insensitive simple patterns (e.g. /[a-z]/i) */


-- 
Langsam's Laws:
	(1) Everything depends.
	(2) Nothing is always.
	(3) Everything is sometimes.

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References to:

"robin.hill@biowisdom.com (via RT)" <perlbug-followup@perl.org>
Dave Mitchell <davem@iabyn.com>
Nicholas Clark <nick@ccl4.org>
Dave Mitchell <davem@iabyn.com>

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