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[perl #122556] DESTROY handler not firing until after function return.

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From:
felipe @ felipegasper . com
Date:
August 20, 2014 16:20
Subject:
[perl #122556] DESTROY handler not firing until after function return.
Message ID:
rt-4.0.18-6253-1408388339-264.122556-75-0@perl.org
# New Ticket Created by  felipe@felipegasper.com 
# Please include the string:  [perl #122556]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=122556 >



This is a bug report for perl from felipe@felipegasper.com,
generated with the help of perlbug 1.39 running under perl 5.14.4.


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

Consider the following:

==============================
#!/usr/bin/perl

package Thingie;

use Carp;

sub DESTROY { print Carp::longmess() }

package main;

use strict;
use warnings;

sub body {
    sub {
        my $t = bless [], 'Thingie';
        undef $t;

        #When the below is commented out, $t isn't garbage-collected until
        #body()'s return. When it's uncommented, $t is garbage-collected
        #right here.
        #
        #return;    #<== UNCOMMENT, AND COMPARE Carp::longmess OUTPUT.
    }->();

    return;
}

body();
====================

When the "undef $t" is the last statement in the anonymous sub, Perl is waiting until after that scope is finished to do the GC. This runs counter to expectation since the last reference to the Thingie is removed by setting $t to undef.

Moreover, this can produce errors if Thingie references a global in its DESTROY and the anonsub did a "local" on that global.

The proper course would seem to be to do GC within the scope. The fact that Perl doesn't behave this way currently looks to me like a bug.

[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
    category=core
    severity=medium
---
Site configuration information for perl 5.14.4:

Configured by cPanel at Thu Jul 10 15:51:11 CDT 2014.

Summary of my perl5 (revision 5 version 14 subversion 4) configuration:
   
  Platform:
    osname=linux, osvers=2.6.32-358.23.2.el6.i686, archname=i386-linux-64int
    uname='linux rpmb-32-centos-6 2.6.32-358.23.2.el6.i686 #1 smp wed oct 16 17:21:31 utc 2013 i686 i686 i386 gnulinux '
    config_args='-des -Dusedevel -Darchname=i386-linux-64int -Dcc=/usr/bin/gcc -Dcpp=/usr/bin/cpp -DDEBUGGING=none -Doptimize=-Os -Dusemymalloc=n -Duseshrplib -Duselargefiles=yes -Duseposix=true -Dhint=recommended -Duseperlio=yes -Dccflags=-I/usr/local/cpanel/3rdparty/perl/514/include -L/usr/local/cpanel/3rdparty/perl/514/lib -I/usr/local/cpanel/3rdparty/include -L/usr/local/cpanel/3rdparty/lib -DAPPLLIB_EXP="/usr/local/cpanel" -Dcppflags=-I/usr/local/cpanel/3rdparty/perl/514/include -L/usr/local/cpanel/3rdparty/perl/514/lib -I/usr/local/cpanel/3rdparty/include -L/usr/local/cpanel/3rdparty/lib -Dldflags=-Wl,-rpath -Wl,/usr/local/cpanel/3rdparty/perl/514/lib -L/usr/local/cpanel/3rdparty/perl/514/lib -L/usr/local/cpanel/3rdparty/lib -Dprefix=/usr/local/cpanel/3rdparty/perl/514 -Dsiteprefix=/opt/cpanel/perl5/514 -Dsitebin=/opt/cpanel/perl5/514/bin -Dsitelib=/opt/cpanel/perl5/514/site_lib -Dusevendorprefix=true -Dvendorbin=/usr/local/cpanel/3rdparty/perl/514/bin -Dvendorprefix=/u
 sr/local/cpanel/3rdparty/perl/514/lib/perl5 -Dvendorlib=/usr/local/cpanel/3rdparty/perl/514/lib/perl5/cpanel_lib -Dprivlib=/usr/local/cpanel/3rdparty/perl/514/lib/perl5/5.14.4 -Dman1dir=none -Dman3dir=none -Dscriptdir=/usr/local/cpanel/3rdparty/perl/514/bin -Dscriptdirexp=/usr/local/cpanel/3rdparty/perl/514/bin -Dsiteman1dir=none -Dsiteman3dir=none -Dinstallman1dir=none -Dversiononly=no -Dinstallusrbinperl=no -Dcf_by=cPanel -Dmyhostname=localhost -Dperladmin=root@localhost -Dcf_email=support@cpanel.net -Di_dbm=/usr/local/cpanel/3rdparty/include -Di_gdbm=/usr/local/cpanel/3rdparty/include -Di_ndbm=/usr/local/cpanel/3rdparty/include -Ud_dosuid -Uuserelocatableinc -Umad -Uusethreads -Uusemultiplicity -Uusesocks -Uuselongdouble -Ui_db -Aldflags=-L/usr/local/cpanel/3rdparty/perl/514/lib -L/usr/local/cpanel/3rdparty/lib -L/usr/lib -L/lib -lgdbm -Dlocincpth=/usr/local/cpanel/3rdparty/perl/514/include /usr/local/cpanel/3rdparty/include /usr/local/include  -Duse64bitint -Uuse64bitall
  -Acflags=-fPIC -DPIC -m32 -I/usr/local/cpanel/3rdparty/perl/514/include -I/usr/local/cpanel/3rdparty/include -Dlibpth=/usr/local/cpanel/3rdparty/perl/514/lib /usr/local/cpanel/3rdparty/lib /usr/local/lib /lib /usr/lib '
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=undef, usemultiplicity=undef
    useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
    use64bitint=define, use64bitall=undef, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='/usr/bin/gcc', ccflags ='-I/usr/local/cpanel/3rdparty/perl/514/include -L/usr/local/cpanel/3rdparty/perl/514/lib -I/usr/local/cpanel/3rdparty/include -L/usr/local/cpanel/3rdparty/lib -DAPPLLIB_EXP="/usr/local/cpanel" -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-Os',
    cppflags='-I/usr/local/cpanel/3rdparty/perl/514/include -L/usr/local/cpanel/3rdparty/perl/514/lib -I/usr/local/cpanel/3rdparty/include -L/usr/local/cpanel/3rdparty/lib -I/usr/local/cpanel/3rdparty/perl/514/include -L/usr/local/cpanel/3rdparty/perl/514/lib -I/usr/local/cpanel/3rdparty/include -L/usr/local/cpanel/3rdparty/lib -DAPPLLIB_EXP="/usr/local/cpanel" -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
    ccversion='', gccversion='4.4.7 20120313 (Red Hat 4.4.7-3)', 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=4, prototype=define
  Linker and Libraries:
    ld='/usr/bin/gcc', ldflags ='-Wl,-rpath -Wl,/usr/local/cpanel/3rdparty/perl/514/lib -L/usr/local/cpanel/3rdparty/perl/514/lib -L/usr/local/cpanel/3rdparty/lib -L/usr/local/cpanel/3rdparty/perl/514/lib -L/usr/local/cpanel/3rdparty/lib -L/usr/lib -L/lib -lgdbm -fstack-protector -L/usr/local/lib'
    libpth=/usr/local/lib /lib /usr/lib
    libs=-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc
    perllibs=-lnsl -ldl -lm -lcrypt -lutil -lc
    libc=/lib/libc-2.12.so, so=so, useshrplib=true, libperl=libperl.so
    gnulibc_version='2.12'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E -Wl,-rpath,/usr/local/cpanel/3rdparty/perl/514/lib/perl5/5.14.4/i386-linux-64int/CORE'
    cccdlflags='-fPIC', lddlflags='-shared -Os -L/usr/local/cpanel/3rdparty/perl/514/lib -L/usr/local/cpanel/3rdparty/lib -L/usr/lib -L/lib -L/usr/local/lib -fstack-protector'

Locally applied patches:
    cPanel patches
    cPanel INC path changes
    Disabled some unstable tests on a kvm build server
    Cherry pick of 49498ca from p5p (RT 113514)
    Remove improper use of each() in B::walksymtable (5cc8528c90)

---
@INC for perl 5.14.4:
    /usr/local/cpanel
    /usr/local/cpanel
    /usr/local/cpanel/3rdparty/perl/514/lib/perl5/cpanel_lib/i386-linux-64int
    /usr/local/cpanel/3rdparty/perl/514/lib/perl5/cpanel_lib
    /usr/local/cpanel/3rdparty/perl/514/lib/perl5/5.14.4/i386-linux-64int
    /usr/local/cpanel/3rdparty/perl/514/lib/perl5/5.14.4
    /opt/cpanel/perl5/514/site_lib/i386-linux-64int
    /opt/cpanel/perl5/514/site_lib
    .

---
Environment for perl 5.14.4:
    HOME=/root
    LANG=en_US.UTF-8
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/root/.opt/bin:/usr/local/cpanel/3rdparty/perl/514/bin:/usr/local/cpanel/3rdparty/bin:/usr/local/cpanel/3rdparty/node/bin:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
    PERL5LIB=/usr/local/cpanel
    PERL_BADLANG (unset)
    SHELL=/bin/bash


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