[perl #75792] Unexpected nested closure circular reference (possibly a Scalar::Util::weaken issue?)

# New Ticket Created by  Peter Rabbitson 
# Please include the string:  [perl #75792]
# in the subject line of all future correspondence about this issue. 
# <URL: http://rt.perl.org/rt3/Ticket/Display.html?id=75792 >


This is a bug report for perl from ribasushi@cpan.org,
generated with the help of perlbug 1.39 running under perl 5.10.1.


-----------------------------------------------------------------
[Please describe your issue here]

During the construction of the following:

A hashref H containing a reference to a coderef C which is a closure
iver a *weakened* reference WH of the original hashref H

A leak is introduced IFF the code inserting C into H is implemented
as a coderef (as opposed to a block).

To illustrate:

This does not leak
=======================================
sub scoped_factory {
   my $self = {};

   {
     my $weakself = $self;
     weaken $weakself;
     $self->{coderef} = sub { die $weakself if $weakself };
   }

   $self;
}


This leaks $self (and everything below)
========================================
sub closure_factory {
   my $self = {};

   sub {
     my $weakself = $self;
     weaken $weakself;
     $self->{coderef} = sub { die $weakself if $weakself };
   }->();

   $self;
}


The issue has been reproduced on all versions of perl from 5.8 on,
including bleadperl. It was originally discovered when an eval {}
was switched to try{} from Try::Tiny in a piece of code installing
DESTROY guards

Attached a test with various invocations of the "constructor"

[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
     category=core
     severity=medium
---
Site configuration information for perl 5.10.1:

Configured by Debian Project at Sun May 30 22:40:05 UTC 2010.

Summary of my perl5 (revision 5 version 10 subversion 1) configuration:

   Platform:
     osname=linux, osvers=2.6.32.14-dsa-ia32, archname=i486-linux-gnu-thread-multi
     uname='linux murphy 2.6.32.14-dsa-ia32 #1 smp thu may 27 16:19:20 cest 2010 i686 gnulinux '
     config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN -Dcccdlflags=-fPIC -Darchname=i486-linux-gnu -Dprefix=/usr -Dprivlib=/usr/share/perl/5.10 -Darchlib=/usr/lib/perl/5.10 -Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5 -Dvendorarch=/usr/lib/perl5 -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl/5.10.1 -Dsitearch=/usr/local/lib/perl/5.10.1 -Dman1dir=/usr/share/man/man1 -Dman3dir=/usr/share/man/man3 -Dsiteman1dir=/usr/local/man/man1 -Dsiteman3dir=/usr/local/man/man3 
-Dman1ext=1 -Dman3ext=3perl -Dpager=/usr/bin/sensible-pager -Uafs -Ud_csh -Ud_ualarm -Uusesfio -Uusenm -DDEBUGGING=-g -Doptimize=-O2 -Duseshrplib -Dlibperl=libperl.so.5.10.1 -Dd_dosuid -des'
     hint=recommended, useposix=true, d_sigaction=define
     useithreads=define, usemultiplicity=define
     useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
     use64bitint=undef, use64bitall=undef, uselongdouble=undef
     usemymalloc=n, bincompat5005=undef
   Compiler:
     cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
     optimize='-O2 -g',
     cppflags='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
     ccversion='', gccversion='4.4.4', gccosandvers=''
     intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
     d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
     ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
     alignbytes=4, prototype=define
   Linker and Libraries:
     ld='cc', ldflags =' -fstack-protector -L/usr/local/lib'
     libpth=/usr/local/lib /lib /usr/lib /usr/lib64
     libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt
     perllibs=-ldl -lm -lpthread -lc -lcrypt
     libc=/lib/libc-2.11.1.so, so=so, useshrplib=true, libperl=libperl.so.5.10.1
     gnulibc_version='2.11.1'
   Dynamic Linking:
     dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
     cccdlflags='-fPIC', lddlflags='-shared -O2 -g -L/usr/local/lib -fstack-protector'

Locally applied patches:
     DEBPKG:debian/arm_thread_stress_timeout - http://bugs.debian.org/501970 Raise the timeout of ext/threads/shared/t/stress.t to accommodate slower build hosts
     DEBPKG:debian/cpan_config_path - Set location of CPAN::Config to /etc/perl as /usr may not be writable.
     DEBPKG:debian/cpan_definstalldirs - Provide a sensible INSTALLDIRS default for modules installed from CPAN.
     DEBPKG:debian/db_file_ver - http://bugs.debian.org/340047 Remove overly restrictive DB_File version check.
     DEBPKG:debian/doc_info - Replace generic man(1) instructions with Debian-specific information.
     DEBPKG:debian/enc2xs_inc - http://bugs.debian.org/290336 Tweak enc2xs to follow symlinks and ignore missing @INC directories.
     DEBPKG:debian/errno_ver - http://bugs.debian.org/343351 Remove Errno version check due to upgrade problems with long-running processes.
     DEBPKG:debian/extutils_hacks - Various debian-specific ExtUtils changes
     DEBPKG:debian/fakeroot - Postpone LD_LIBRARY_PATH evaluation to the binary targets.
     DEBPKG:debian/instmodsh_doc - Debian policy doesn't install .packlist files for core or vendor.
     DEBPKG:debian/ld_run_path - Remove standard libs from LD_RUN_PATH as per Debian policy.
     DEBPKG:debian/libnet_config_path - Set location of libnet.cfg to /etc/perl/Net as /usr may not be writable.
     DEBPKG:debian/m68k_thread_stress - http://bugs.debian.org/495826 Disable some threads tests on m68k for now due to missing TLS.
     DEBPKG:debian/mod_paths - Tweak @INC ordering for Debian
     DEBPKG:debian/module_build_man_extensions - http://bugs.debian.org/479460 Adjust Module::Build manual page extensions for the Debian Perl policy
     DEBPKG:debian/perl_synopsis - http://bugs.debian.org/278323 Rearrange perl.pod
     DEBPKG:debian/prune_libs - http://bugs.debian.org/128355 Prune the list of libraries wanted to what we actually need.
     DEBPKG:debian/use_gdbm - Explicitly link against -lgdbm_compat in ODBM_File/NDBM_File.
     DEBPKG:fixes/assorted_docs - http://bugs.debian.org/443733 [384f06a] Math::BigInt::CalcEmu documentation grammar fix
     DEBPKG:fixes/net_smtp_docs - http://bugs.debian.org/100195 [rt.cpan.org #36038] Document the Net::SMTP 'Port' option
     DEBPKG:fixes/processPL - http://bugs.debian.org/357264 [rt.cpan.org #17224] Always use PERLRUNINST when building perl modules.
     DEBPKG:debian/perlivp - http://bugs.debian.org/510895 Make perlivp skip include directories in /usr/local
     DEBPKG:fixes/pod2man-index-backslash - http://bugs.debian.org/521256 Escape backslashes in .IX entries
     DEBPKG:debian/disable-zlib-bundling - Disable zlib bundling in Compress::Raw::Zlib
     DEBPKG:fixes/kfreebsd_cppsymbols - http://bugs.debian.org/533098 [3b910a0] Add gcc predefined macros to $Config{cppsymbols} on GNU/kFreeBSD.
     DEBPKG:debian/cpanplus_definstalldirs - http://bugs.debian.org/533707 Configure CPANPLUS to use the site directories by default.
     DEBPKG:debian/cpanplus_config_path - Save local versions of CPANPLUS::Config::System into /etc/perl.
     DEBPKG:fixes/kfreebsd-filecopy-pipes - http://bugs.debian.org/537555 [16f708c] Fix File::Copy::copy with pipes on GNU/kFreeBSD
     DEBPKG:fixes/anon-tmpfile-dir - http://bugs.debian.org/528544 [perl #66452] Honor TMPDIR when open()ing an anonymous temporary file
     DEBPKG:fixes/abstract-sockets - http://bugs.debian.org/329291 [89904c0] Add support for Abstract namespace sockets.
     DEBPKG:fixes/hurd_cppsymbols - http://bugs.debian.org/544307 [eeb92b7] Add gcc predefined macros to $Config{cppsymbols} on GNU/Hurd.
     DEBPKG:fixes/autodie-flock - http://bugs.debian.org/543731 Allow for flock returning EAGAIN instead of EWOULDBLOCK on linux/parisc
     DEBPKG:fixes/archive-tar-instance-error - http://bugs.debian.org/539355 [rt.cpan.org #48879] Separate Archive::Tar instance error strings from each other
     DEBPKG:fixes/positive-gpos - http://bugs.debian.org/545234 [perl #69056] [c584a96] Fix \\G crash on first match
     DEBPKG:debian/devel-ppport-ia64-optim - http://bugs.debian.org/548943 Work around an ICE on ia64
     DEBPKG:fixes/trie-logic-match - http://bugs.debian.org/552291 [perl #69973] [0abd0d7] Fix a DoS in Unicode processing [CVE-2009-3626]
     DEBPKG:fixes/hppa-thread-eagain - http://bugs.debian.org/554218 make the threads-shared test suite more robust, fixing failures on hppa
     DEBPKG:fixes/crash-on-undefined-destroy - http://bugs.debian.org/564074 [perl #71952] [1f15e67] Fix a NULL pointer dereference when looking for a DESTROY method
     DEBPKG:fixes/tainted-errno - http://bugs.debian.org/574129 [perl #61976] [be1cf43] fix an errno stringification bug in taint mode
     DEBPKG:fixes/safe-upgrade - http://bugs.debian.org/582978 Upgrade Safe.pm to 2.25, fixing CVE-2010-1974
     DEBPKG:fixes/tell-crash - http://bugs.debian.org/578577 [f4817f3] Fix a tell() crash on bad arguments.
     DEBPKG:fixes/format-write-crash - http://bugs.debian.org/579537 [perl #22977] [421f30e] Fix a crash in format/write
     DEBPKG:fixes/arm-alignment - http://bugs.debian.org/289884 Prevent gcc from optimizing the alignment test away on armel
     DEBPKG:fixes/fcgi-test - Fix a failure in CGI/t/fast.t when FCGI is installed
     DEBPKG:patchlevel - http://bugs.debian.org/567489 List packaged patches for 5.10.1-13 in patchlevel.h

---
@INC for perl 5.10.1:
     /home/rabbit/devel/utils/perl
     /home/rabbit/LOCAL_PERL5/lib/perl5/i486-linux-gnu-thread-multi
     /home/rabbit/LOCAL_PERL5/lib/perl5
     /home/rabbit/LOCAL_PERL5/lib/perl5/i486-linux-gnu-thread-multi
     /etc/perl
     /usr/local/lib/perl/5.10.1
     /usr/local/share/perl/5.10.1
     /usr/lib/perl5
     /usr/share/perl5
     /usr/lib/perl/5.10
     /usr/share/perl/5.10
     /usr/local/lib/site_perl
     .

---
Environment for perl 5.10.1:
     HOME=/home/rabbit
     LANG=en_US.UTF-8
     LANGUAGE (unset)
     LC_ADDRESS=en_US.UTF-8
     LC_COLLATE=en_US.UTF-8
     LC_CTYPE=en_US.UTF-8
     LC_IDENTIFICATION=en_US.UTF-8
     LC_MESSAGES=en_US.UTF-8
     LC_MONETARY=en_US.UTF-8
     LC_NAME=en_US.UTF-8
     LC_NUMERIC=en_US.UTF-8
     LC_TELEPHONE=en_US.UTF-8
     LC_TIME=en_US.UTF-8
     LD_LIBRARY_PATH (unset)
     LOGDIR (unset)
     PATH=/home/rabbit/devel/utils:/home/rabbit/perl5/perlbrew/bin:/home/rabbit/perl5/perlbrew/perls/current/bin:/home/rabbit/LOCAL_PERL5/bin:/home/rabbit/bin:/usr/local/bin:/usr/bin:/bin:/usr/games
     PERL5LIB=/home/rabbit/devel/utils/perl:/home/rabbit/LOCAL_PERL5/lib/perl5:/home/rabbit/LOCAL_PERL5/lib/perl5/i486-linux-gnu-thread-multi:
     PERL_AUTOINSTALL_PREFER_CPAN=1
     PERL_BADLANG (unset)
     PERL_MM_OPT=INSTALL_BASE=/home/rabbit/LOCAL_PERL5
     SHELL=/bin/bash

• [perl #75792] Unexpected nested closure circular reference (possibly a Scalar::Util::weaken issue?) by Peter Rabbitson
• Re: [perl #75792] Unexpected nested closure circular reference (possibly a Scalar::Util::weaken issue?) by Bo Lindbergh
• Re: [perl #75792] Unexpected nested closure circular reference(possibly a Scalar::Util::weaken issue?) by Dave Mitchell