[perl #59882] Variable falls out of scope but is not garbage-collected

["fbriere@fbriere.net (via RT)" <perlbug-followup@perl.org>]

# New Ticket Created by  fbriere@fbriere.net 
# Please include the string:  [perl #59882]
# in the subject line of all future correspondence about this issue. 
# <URL: http://rt.perl.org/rt3/Ticket/Display.html?id=59882 >



This is a bug report for perl from fbriere@fbriere.net,
generated with the help of perlbug 1.36 running under perl 5.10.0.


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[Please enter your report here]


#!/usr/bin/perl

# From: Frédéric Brière <fbriere@fbriere.net>
#
# This is a stripped-down version of a bug I hit when combining subclassing
# with Test::MockModule.  Basically, a variable falls out of scope but is not
# garbage-collected, even though there should be no remaining references to
# it.


use 5.006;
use strict;
use warnings;

# Set up fake Parent and Child modules
@Child::ISA = 'Parent';

# Foo's only purpose is to let us know when a variable is garbage-collected
sub Foo::DESTROY { print "The object is being destroyed.\n" }


{
	my $obj = bless {}, 'Foo';

	# Create a fake dummy() method.  Note the reference to $obj.
	*Parent::dummy = sub { $obj->{dummy}++ };
	
	# This is the key part -- calling dummy() via inheritance.
	# Commenting this out, or calling Parent->dummy() directly, will not
	# trigger the bug.
	Child->dummy;

	# Deleting the sub, and thus the reference to $obj
	undef *Parent::dummy;

	# At this point, $obj is falling out of scope, and should be
	# garbage-collected, but will not.  However, explictly undef-ing it
	# *will* make it be collected.  So will calling (via eval) the
	# no-longer-existant Child->dummy().
}

print "The object should have been destroyed at this point.\n";



[Please do not change anything below this line]
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---
Flags:
    category=core
    severity=low
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Site configuration information for perl 5.10.0:

Configured by Debian Project at Tue Sep 30 16:11:07 UTC 2008.

Summary of my perl5 (revision 5 version 10 subversion 0) configuration:
  Platform:
    osname=linux, osvers=2.6.26.1, archname=i486-linux-gnu-thread-multi
    uname='linux ninsei 2.6.26.1 #1 smp preempt sun aug 3 22:34:07 pdt 2008 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/5.10.0 -Dsitearch=/usr/local/lib/perl/5.10.0 -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.5.10.0 -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 -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 -I/usr/local/include'
    ccversion='', gccversion='4.3.2', 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 =' -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-2.7.so, so=so, useshrplib=true, libperl=libperl.so.5.10.0
    gnulibc_version='2.7'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -O2 -g -L/usr/local/lib'

Locally applied patches:
    

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@INC for perl 5.10.0:
    /home/imars/gx/devel/lib
    /home/imars/gx/devel/t/lib
    /etc/perl
    /usr/local/lib/perl/5.10.0
    /usr/local/share/perl/5.10.0
    /usr/lib/perl5
    /usr/share/perl5
    /usr/lib/perl/5.10
    /usr/share/perl/5.10
    /usr/local/lib/site_perl
    .

---
Environment for perl 5.10.0:
    HOME=/home/fbriere
    LANG=en_CA.UTF-8
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/usr/local/bin:/usr/bin:/bin:/usr/games
    PERL5LIB=/home/imars/gx/devel/lib:/home/imars/gx/devel/t/lib
    PERL_BADLANG (unset)
    SHELL=/bin/bash

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Follow-Ups from:

Dave Mitchell <davem@iabyn.com>

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