From @jdhedden

Created by @jdhedden

Here's the test script​:

use threads;

for (1..1) {
  leak($_); # Produces "Scalars leaked​: 1"
  #leak(); # No leaks
}

sub leak
{
  for (1..1) {
  threads->create(sub {})->join();
  }
}

This produces the same result in blead.

Flags:
    category=core
    severity=medium

Site configuration information for perl v5.8.8:

Configured by Jerry at Wed Dec 20 08:14:01 EST 2006.

Summary of my perl5 (revision 5 version 8 subversion 8) configuration:
  Platform:
    osname=cygwin, osvers=1.5.23(0.15642),
archname=cygwin-thread-multi-64int
    uname='cygwin_nt-5.0 pn100-02-2-054p 1.5.23(0.15642) 2006-12-19
10:52 i686 cygwin '
    config_args='-de -Duse64bitint -Dusethreads -Uusemymalloc
-Dnoextensions=attrs IPC/SysV -A define:optimize=-O3 -pipe
-funit-at-a-time -mtune=pentium4m -march=pentium4 -mfpmath=sse
-mieee-fp -mmmx -msse -msse2 -A define:ld=/usr/bin/ld2 -A
append:ccflags= -DPERL_DONT_CREATE_GVSV -DNO_MATHOMS'
    hint=recommended, useposix=true, d_sigaction=define
    usethreads=define use5005threads=undef useithreads=define
usemultiplicity=define
    useperlio=define d_sfio=undef uselargefiles=define usesocks=undef
    use64bitint=define use64bitall=undef uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='gcc', ccflags ='-DPERL_USE_SAFE_PUTENV -DPERL_DONT_CREATE_GVSV
-DNO_MATHOMS -fno-strict-aliasing -pipe -Wdeclaration-after-statement',
    optimize='-O3 -pipe -funit-at-a-time -mtune=pentium4m
-march=pentium4 -mfpmath=sse -mieee-fp -mmmx -msse -msse2',
    cppflags='-DPERL_USE_SAFE_PUTENV -DPERL_DONT_CREATE_GVSV
-DNO_MATHOMS -fno-strict-aliasing -pipe -Wdeclaration-after-statement'
    ccversion='', gccversion='3.4.4 (cygming special, gdc 0.12, using
dmd 0.125)', gccosandvers=''
    intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=12345678
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
    ivtype='long long', ivsize=8, nvtype='double', nvsize=8,
Off_t='off_t', lseeksize=8
    alignbytes=8, prototype=define
  Linker and Libraries:
    ld='/usr/bin/ld2', ldflags =' -s -L/usr/local/lib'
    libpth=/usr/local/lib /usr/lib /lib
    libs=-lgdbm -ldb -ldl -lcrypt -lgdbm_compat
    perllibs=-ldl -lcrypt -lgdbm_compat
    libc=/usr/lib/libc.a, so=dll, useshrplib=true, libperl=libperl.a
    gnulibc_version=''
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=dll, d_dlsymun=undef, ccdlflags=' -s'
    cccdlflags=' ', lddlflags=' -s -L/usr/local/lib'

Locally applied patches:
    MAINT28213
    29163


@INC for perl v5.8.8:
    /usr/lib/perl5/5.8/cygwin
    /usr/lib/perl5/5.8
    .


Environment for perl v5.8.8:
    CYGWIN=server ntsec
    HOME=/home/jhedden
    LANG=C
    LANGUAGE=C
    LC_ALL=C
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
   
PATH=/home/jhedden/bin:/usr/local/bin:/usr/bin:/bin:/usr/X11R6/bin:/c/Perl/bin:/c/djgpp/bin:/c/Program
Files/WiX:/c/Program Files/nant-0.85-rc3/bin:/c/Program
Files/apache-ant-1.6.3/bin:/c/j2sdk1.4.2_08/bin:/c/Program
Files/Documentum/Shared:/c/blp/API:/c/oracle/ora92/bin:/c/Program
Files/Oracle/jre/1.3.1/bin:/c/Program
Files/Oracle/jre/1.1.8/bin:/c/WINNT/system32:/c/WINNT:/c/WINNT/system32/WBEM:/c/Program
Files/cvsnt:/c/Program Files/QuickTime/QTSystem/:/c/dev-cpp/bin/:.
    PERLIO=perlio
    PERL_BADLANG (unset)
    SHELL (unset)

__________________________________________________
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From @iabyn

On Tue, Dec 26, 2006 at 07​:52​:27AM -0800, jdhedden @​ 1979. usna. com wrote​:

Here's the test script​:

use threads;

for (1..1) {
leak($_); # Produces "Scalars leaked​: 1"
#leak(); # No leaks
}

sub leak
{
for (1..1) {
threads->create(sub {})->join();
}
}

This can be reduced to​:

  use threads;

  leak($x);

  sub leak
  {
  local $x;
  threads->create(sub {})->join();
  }

(so it's not specific to $_). It occurs, because at the point the thread
is cloned, the saved $x is referenced from​:
  * the save stack
  * the @​_ array​: which is not refcnted

For threads creation, the save stack isn't duplicated, so the saved $x is
duplicated only via @​_, which isn't refcnted, so the cloned $x gets
created with refcnt=0 and hangs around until thread exit.

Can't see an easy way to fix this.

--
My get-up-and-go just got up and went.

The RT System itself - Status changed from 'new' to 'open'

From @nwc10

On Sun, Jan 07, 2007 at 09​:23​:28PM +0000, Dave Mitchell wrote​:

This can be reduced to​:

use threads;

leak\($x\);

sub leak
\{
local $x;
threads\->create\(sub \{\}\)\->join\(\);
\}

(so it's not specific to $_). It occurs, because at the point the thread
is cloned, the saved $x is referenced from​:
* the save stack
* the @​_ array​: which is not refcnted

For threads creation, the save stack isn't duplicated, so the saved $x is
duplicated only via @​_, which isn't refcnted, so the cloned $x gets
created with refcnt=0 and hangs around until thread exit.

Can't see an easy way to fix this.

For things that are duplicated by the no_inc variants (so implicitly start
out with a reference count of zero in the ptr_table that maps parent to child),
would it work to instead create them with a reference count of one, and
place an entry on the save stack to free that reference?

Nicholas Clark

From guest@guest.guest.xxxxxxxx

On Sun Jan 07 14​:17​:12 2007, nicholas wrote​:

On Sun, Jan 07, 2007 at 09​:23​:28PM +0000, Dave Mitchell wrote​:

This can be reduced to​:

use threads;

leak\($x\);

sub leak
\{
local $x;
threads\->create\(sub \{\}\)\->join\(\);
\}

(so it's not specific to $_). It occurs, because at the point the
thread
is cloned, the saved $x is referenced from​:
* the save stack
* the @​_ array​: which is not refcnted

For threads creation, the save stack isn't duplicated, so the saved
$x is
duplicated only via @​_, which isn't refcnted, so the cloned $x gets
created with refcnt=0 and hangs around until thread exit.

Can't see an easy way to fix this.

For things that are duplicated by the no_inc variants (so implicitly
start
out with a reference count of zero in the ptr_table that maps parent
to child),
would it work to instead create them with a reference count of one,
and
place an entry on the save stack to free that reference?

Nicholas Clark

I have modified the test script and seems to stop this leak​:
sub leak
{
  my $arg = shift; #no leak

  for (1..1)
  {
  threads->create(sub {})->join();
  }
}

Does anyone know what time frame this problem will be fixed?

From @iabyn

fixed in blead with e81cd4d

@iabyn - Status changed from 'open' to 'resolved'

From @jdhedden

On Mon, Jan 11, 2010 at 07​:54, Dave Mitchell via RT
<perlbug-followup@​perl.org> wrote​:

According to our records, your request regarding
 "$_ leaks under threads"
has been resolved.

If you have any further questions or concerns, please respond to this message.

For other topics, please create a new ticket.

Please don't feel obligated to say "Thanks" or "Kudos" or "I owe you a beer" -- if you respond to this message it will reopen the ticket. If you must, please send email directly to the person who handled your ticket, and not to the tracking system.

<URL​: http​://rt.perl.org/rt3/Ticket/Display.html?id=41138 >

This fix also fixes #34342.