RE: memory leak in DBI XS bootstrap code


Did you try the other suggestions?
How much improvement did each give? (when testing by destroying the
interpreter)

Yeah, sorry I didn't give more detail on that. Here goes:

The first change (Doru Petrescu):
No change, still leaks 4 per connect/prepare/execute/fetch/disconnect loop.

The (av_len(av) % 120 == 0) change:
That does reduce it to 3 per loop, but I am not sure what you mean that it is not a leak - when it leaks 4, it's 4 every time - it's not stabilizing after some time, or jumping back down once in a while, or only leaking 3 sometimes, just going up and up by 4 every time. So how is that not a leak?

As I said, the "if (0)" on the whole chunk of code produces squeaky clean iterations.

-edan

So... do I need to keep this patched myself, at the risk of breaking
when the code changes in some future release, or can you somehow make
this optional, or fix it,

I'd probably accept a patch that adds an option to Makefile.PL that then
passes a -DDBI_NO_WEAKREFS to the compiler which, with a suitable
#ifndef in DBI.xs, would disable that code. Or a new per-handle
flag could be added.

But I'm reluctant to do either till I know more about the cause.

or explain to me what I can do to make the
leak go away using the current code?

I need more info - see above.

Tim.

Thanks so much,
edan

-----Original Message-----
From: Tim Bunce [mailto:Tim.Bunce@xxxxxxxxx]
Sent: Tuesday, July 11, 2006 16:59
To: Ephraim Dan
Cc: Tim Bunce; dbi-users@xxxxxxxx
Subject: Re: memory leak in DBI XS bootstrap code

I'm sorry but I simply don't have the time at the moment.

Some random suggestions:
- try using different sets of methods to isolate the minimum
requirements.
for example:
call fetchrow_array just once.
don't call fetchrow_array at all.
call fetchrow_array in loop but don't call finish
don't execute, fetch, finish.
etc etc etc
- try with other drivers to see if it's the driver or the DBI
that's
leaking

Tim.

On Tue, Jul 11, 2006 at 03:59:05AM -0700, Ephraim Dan wrote:
Tim,

I'm experiencing further memory leaks which are causing me more
grief.
I put together the following test script which illustrates the
leakage:

#/usr/bin/perl
# dbi.pl

use DBI;
use Devel::Leak;
my $leak_handle;

for ( 1 .. 1000 ) {
my $dbh = DBI->connect("DBI:mysql:MYDB","user","secret",
{RaiseError=>1});
my $sth = $dbh->prepare("SELECT COUNT(*) FROM TABLE");
$sth->execute();
while ( my ($c) = $sth->fetchrow_array() ) {
# print "$c\n";
}
$sth->finish;
$dbh->disconnect;

system("ps -aux | fgrep dbi.pl | fgrep -v fgrep");
test_leak();
}

sub test_leak {
if ( $handle ) {
Devel::Leak::CheckSV($handle);
}
print STDERR "count: " . Devel::Leak::NoteSV($handle) . "\n";
}

Devel::Leak shows that it is leaking 4 "things" every iteration:

count: 12128
root 17720 17.8 0.3 6840 4220 pts/0 S 09:55 0:00
perl
dbi.pl
new 0x8aad3e8 : SV = PVHV(0x8a68b30) at 0x8aad3e8
REFCNT = 1
FLAGS = (PADBUSY,PADMY,SHAREKEYS)
IV = 0
NV = 0
ARRAY = 0x0
KEYS = 0
FILL = 0
MAX = 7
RITER = -1
EITER = 0x0
new 0x8aad3f4 : SV = NULL(0x0) at 0x8aad3f4
REFCNT = 1
FLAGS = (PADBUSY,PADMY)
new 0x8aad400 : SV = NULL(0x0) at 0x8aad400
REFCNT = 1
FLAGS = (PADBUSY,PADMY)
new 0x8aad40c : SV = NULL(0x0) at 0x8aad40c
REFCNT = 1
FLAGS = (PADBUSY,PADMY)
count: 12132

I think there might be several leaks here. If I move the
connect()
out
of the loop, it's leaking, but less - just one of those NULL SV
guys.

Can you please help me track this down? I'm still a little
scared
of
the DBI.xs internals, despite my recent exposure...

Thanks a lot,
edan


-----Original Message-----
From: Tim Bunce [mailto:Tim.Bunce@xxxxxxxxx]
Sent: Monday, July 03, 2006 12:16
To: Ephraim Dan
Cc: Tim Bunce; dbi-users@xxxxxxxx
Subject: Re: memory leak in DBI XS bootstrap code

On Sat, Jul 01, 2006 at 10:42:58PM -0700, Ephraim Dan wrote:
Thanks for the help Tim! You've really done me a great
service.

I have created the following patch, which appears to fix all
of
the
leaks. Can you please review it, and give it your stamp of
approval?
I
am willing to use this patch if you approve it, until a new
DBI is
available with the fixes.

Looks okay at first sight, except that Newz returns memory
that's
been
reset to zero bytes. You need to add the memzero I suggested
previously.
Might as well go into malloc_using_sv since it's not
performance
critical.

Um, looks like CLONE plus _clone_dbis plus dbi_bootinit
already do
the
right thing (your patch also fixes a leak on thread creation)
so
that's
okay. INIT_PERINTERP is harder to be sure about, but I think
it's
okay.

I'll apply the patch and add the memzero. Thanks edan.

Tim.

Thanks again,
edan

The patch:

--- DBI.xs.orig 2006-06-30 10:20:10.000000000 -0400
+++ DBI.xs 2006-07-02 04:59:32.000000000 -0400
@@ -171,7 +171,7 @@
dPERINTERP_SV; dPERINTERP_PTR(PERINTERP_t *,
PERINTERP)
# define INIT_PERINTERP \
dPERINTERP;
\
- Newz(0,PERINTERP,1,PERINTERP_t);
\
+ PERINTERP = malloc_using_sv(sizeof(PERINTERP_t));
\
sv_setiv(perinterp_sv, PTR2IV(PERINTERP))

# undef DBIS
@@ -209,13 +209,29 @@
stc_s, sizeof(dbih_stc_t), fdc_s,
sizeof(dbih_fdc_t),
msg);
}

+static void *
+malloc_using_sv(STRLEN len)
+{
+ dTHX;
+ SV *sv = newSV(len);
+ return SvPVX(sv);
+}
+
+static char *
+savepv_using_sv(char *str)
+{
+ char *buf = malloc_using_sv(strlen(str));
+ strcpy(buf, str);
+ return buf;
+}
+
static void
dbi_bootinit(dbistate_t * parent_dbis)
{
dTHX;
INIT_PERINTERP;

- Newz(dummy, DBIS, 1, dbistate_t);
+ DBIS = (struct
dbistate_st*)malloc_using_sv(sizeof(struct
dbistate_st));

/* store version and size so we can spot DBI/DBD
version
mismatch
*/
DBIS->check_version = check_version;
@@ -3793,7 +3809,7 @@
ima->minargs = (U8)SvIV(*av_fetch(av, 0, 1));
ima->maxargs = (U8)SvIV(*av_fetch(av, 1, 1));
svp = av_fetch(av, 2, 0);
- ima->usage_msg = savepv( (svp) ? SvPV(*svp,lna)
:
"");
+ ima->usage_msg = (svp) ?
savepv_using_sv(SvPV(*svp,
lna)) :
"";
ima->flags |= IMA_HAS_USAGE;
if (trace_msg && DBIS_TRACE_LEVEL >= 11)
sv_catpvf(trace_msg, ",\n usage: min %d,
max
%d,
'%s'",

-----Original Message-----
From: Tim Bunce [mailto:Tim.Bunce@xxxxxxxxx]
Sent: Friday, June 30, 2006 16:33
To: Ephraim Dan
Cc: Tim Bunce; dbi-users@xxxxxxxx
Subject: Re: memory leak in DBI XS bootstrap code

On Fri, Jun 30, 2006 at 04:08:46AM -0700, Ephraim Dan
wrote:
This is why I love the perl community - you're
willing to
help
even
though you don't have time, since
you care about your code, and that other people can
benefit
from
it.

But ... you sort of left a dangling "But" in your
last
post.
Do
you
have a suggestion to fix the
_install_method problem?

I just ran valgrind with your fix - there seems to
still
be a
leak.
It is reported on DBI.xs line 216:
INIT_PERINTERP;
That looks to also have a Newz in it - is that what
leaks?

Yes. It's basically a plain malloc and there's no
mechanism to
free it
later.

Can you suggest how to fix that one?

The trick is to use newSV to alloc memory in the form of
an SV
so that when the interpreter is destroyed the SV memory
gets
freed
automatically.

The _install_method leak is reported on line 3800 (in
my
modified
DBI.xs) which validates your theory:
ima->usage_msg = savepv( (svp) ? SvPV(*svp,lna) :
"");
If you can fix these, I'll be forever in your debt...

As above, and as outlined previously, use an SV.
Something like this (completely untested):

static void *
malloc_using_sv(STRLEN len) {
SV *sv = newSV(len);
return SvPVX(sv);
}

static char *
savepv_using_sv(char *str) {
char *buf = malloc_using_sv(strlen(str));
strcpy(buf, str);
return buf;
}

Tim.

--edan

-----------------------------------------------------
----
----
----
----
-----------------------------------

From: Tim Bunce [mailto:Tim.Bunce@xxxxxxxxx]
Sent: Fri 6/30/2006 11:35
To: Ephraim Dan
Cc: Tim Bunce; dbi-users@xxxxxxxx
Subject: Re: memory leak in DBI XS bootstrap code

On Fri, Jun 30, 2006 at 12:24:33AM -0700, Ephraim Dan
wrote:
> > > I don't see what you mean in the "INSTALL" that
comes
with
perl
5.8.0 (that's what we're using).
> > The file called INSTALL in the perl source code
directory.
>
> That I knew. What are the special instructions
that
I'm
supposed
to
> find there? Am I supposed to build it with
debugging?
Can
you
> specify what special configuration exactly you
meant
that I
should
use?

I'm sorry. I should have checked myself first. You
can
build
perl
with
-DPURIFY to enable more precise leak detection.

> It looks like the leak in boot_DBI is on purpose:
> /* Remember the last handle used. BEWARE!
Sneaky
stuff
here!
*/
> /* We want a handle reference but we don't want
to
increment
*/
> /* the handle's reference count and we don't
want
perl
to
try
*/
> /* to destroy it during global destruction.
Take
care!
*/
> DBI_UNSET_LAST_HANDLE; /* ensure setup the
correct
way
*/
>
> Why is this being done, and does anyone have a way
to
fix
it?
Why
don't we want perl to destroy it?
Me, that's exactly what I want.

I don't believe that's a leak. It's just using an SV
as a
reference
without telling perl its a reference. If perl knew it
was
a
reference
we'd get double-free warnings as the referenced value
would
be
freed
twice.

The leak is probably the DBIS structure itself:

Newz(dummy, DBIS, 1, dbistate_t);

That should probably be using along the lines of:

sv = newSV(sizeof(struct dbistate_st));
DBIS = (struct dbistate_st*)SvPVX(sv);
memzero(DBIS, sizeof(struct dbistate_st));

So the memory is allocated within an SV so gets freed
on
global
destruction.

> Still looking into the other leak in
_install_method...
any
pointers still appreciated... Thanks for
your help so far, Tim.

I've taken a look at the code. I'd guess that it's
due to
savepnv:

ima->usage_msg = savepv( (svp) ? SvPV(*svp,lna)
:
"");

But

Tim.

> -edan
>
> > > -----Original Message-----
> > > From: Tim Bunce [[1]mailto:Tim.Bunce@xxxxxxxxx]
> > > Sent: Thursday, June 29, 2006 14:47
> > > To: Ephraim Dan
> > > Cc: dbi-users@xxxxxxxx
> > > Subject: Re: memory leak in DBI XS bootstrap
code
> > >
> > > Try building perl with options to make valgrind
leak
tracing
more
> > > effective (see perl's INSTALL file). That may
help
you
pinpoint
> > > the problem.
> > >
> > > Tim.
> > >
> > > On Thu, Jun 29, 2006 at 04:33:40AM -0700,
Ephraim
Dan
wrote:
> > > > I am experiencing what I believe to be a
memory
leak
in
the
DBI
> > > bootstrap code. This is a problem for me
because I
am
embedding perl in a
> > > long-running program, and DBI is being loaded
over
and
over, so
my program
> > > grows and grows.
> > > >
> > > > The problem appears to be in the following
routines:
> > > >
> > > > boot_DBI (in
/usr/lib/perl5/vendor_perl/5.8.0/i386-
linux-
thread-
> > > multi/auto/DBI/DBI.so)
> > > > XS_DBI__install_method (in
/usr/lib/perl5/vendor_perl/5.8.0/i386-linux-
> > > thread-multi/auto/DBI/DBI.so)
> > > >
> > > > I am using DBI 1.51
> > > >
> > > > The tool "valgrind" ([2]http://valgrind.org
<[3]http://valgrind.org/> ) can be used to reproduce
the
> > > leak using the following code:
> > > >
> > > > ---
> > > > File: embed_test.c
> > > > ---
> > > >
> > > > #include <EXTERN.h> /* from the
Perl
distribution */
> > > > #include <perl.h> /* from the
Perl
distribution */
> > > >
> > > > static PerlInterpreter *my_perl; /*** The
Perl
interpreter ***/
> > > > EXTERN_C void xs_init (pTHX); /***
init
dyn.
loading
***/
> > > >
> > > > int main(int argc, char **argv, char **env)
> > > > {
> > > > char *embedding[] = { "", "-e", "0" };
> > > > my_perl = perl_alloc();
> > > > perl_construct(my_perl);
> > > > perl_parse(my_perl, xs_init, 3,
embedding,
(char
**)NULL);
> > > > PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
> > > > perl_run(my_perl);
> > > > eval_pv("use DBI", TRUE);
> > > > perl_destruct(my_perl);
> > > > perl_free(my_perl);
> > > > }
> > > >
> > > > ---
> > > > File: Makefile
> > > > ---
> > > >
> > > > CC_OPTS = $(shell perl -MExtUtils::Embed -e
ccopts)
> > > > LD_OPTS = $(shell perl -MExtUtils::Embed -e
ldopts)
> > > >
> > > > EXE = embed_test
> > > >
> > > > $(EXE): xsinit.o embed_test.o
> > > > gcc -o $(EXE) embed_test.o xsinit.o
$(LD_OPTS)
> > > >
> > > > embed_test.o: embed_test.c
> > > > gcc -c embed_test.c $(CC_OPTS)
> > > >
> > > > xsinit.o: xsinit.c
> > > > gcc -c xsinit.c $(CC_OPTS)
> > > >
> > > > xsinit.c:
> > > > perl -MExtUtils::Embed -e xsinit -- -
o
xsinit.c
> > > >
> > > > clean:
> > > > rm -f *.o xsinit.c $(EXE)
> > > >
> > > > ---
> > > > EOF
> > > > ---
> > > >
> > > > Can anyone suggest a fix for this? I'd be
more
than
willing
to take a
> > > patch to DBI 1.51 as soon as someone has one.
> > > >
> > > > Thanks,
> > > > Ephraim Dan
> > > >
>

References

Visible links
1. mailto:Tim.Bunce@xxxxxxxxx
2. http://valgrind.org/
3. http://valgrind.org/

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