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[perl #130649] Threads, shared memory, blessed objects fail to call->DESTROY method

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From:
V Burns
Date:
January 26, 2017 14:02
Subject:
[perl #130649] Threads, shared memory, blessed objects fail to call->DESTROY method
Message ID:
rt-4.0.24-11114-1485434330-1009.130649-75-0@perl.org
# New Ticket Created by  V Burns 
# Please include the string:  [perl #130649]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=130649 >


This is a bug report for Perl from victor.burns@bankofamerica.com,
generated with the help of perlbug 1.39 running under perl 5.12.2.


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

This issue is believed to exist in all 5.10.1+ Perl's and every older Perl as well.
I have verified the issue in every Perl I have at my disposal from 5.10.1, 5.12.0, 5.22.0 and 5.24.0.

Description:
If the last reference to an object is in thread shared memory the objects
DESTROY method won't be called or highly unlikely to be called. This is a
*huge* problem for applications that are OO and designed using composition
of other classes (HAS-A). The last, and possibly only reference will be in
Perl's thread shared memory. I think the real issue only resembles my
description and therefore it is not perfect. I have however included a
small script that when used and modified as the comments suggest the
related behaviors may be observed. The actual issue is a bit more
unpredictable.

## PERL BUG Example

use 5.010001;
use strict;
use warnings;
use threads;
use threads::shared;

our $VERSION = 0.1;

say 'Hello World!, - Perl shared memory failure to call ->DESTROY detector.';

LEAKER:
{
  ## Using the "shared" attribute can play a role in this
  ##  Best guess it means all references are shared.
  my $aa :shared = bless &share({}), 'Lazy::Crazy';
  my $bb :shared = bless &share({}), 'Lazy::Crazy';
  my $cc :shared = &share( bless {}, 'Lazy::Crazy' );

  ## Placing an object into another makes it a sure bet its
  ##  ->DESTROY won't be called
  $aa->{ has_c } = $cc;
  $bb->{ has_a } = $aa;

  ## It's strange that the order of the following assignments
  ##  will allow the last one touched to call its ->DESTROY
  $cc->{ label } = 'c';
  $aa->{ label } = 'a';
  $bb->{ label } = 'b';

  ## If I'm able to control the order these are unwrapped (destroyed)
  ##  things start working as expected.
  ##    How likely can I always get this right, not at all!
  ## (uncomment and things work as expected)
# $bb = undef;
# $aa = undef;
# $cc = undef;
}

package Lazy::Crazy;

sub DESTROY
{
  my $self = shift;
  printf "# %s '%s' is destroyed\n", ref $self, $self->{ label };
  return;
}

## END

[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
    category=library
    severity=high
    module=threads::shared
---
Site configuration information for perl 5.12.2:

Configured by SYSTEM at Mon Sep  6 23:12:49 2010.

Summary of my perl5 (revision 5 version 12 subversion 2) configuration:
   
  Platform:
    osname=MSWin32, osvers=5.00, archname=MSWin32-x86-multi-thread
    uname=''
    config_args='undef'
    hint=recommended, useposix=true, d_sigaction=undef
    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='cl', ccflags ='-nologo -GF -W3 -MD -Zi -DNDEBUG -O1 -DWIN32 -D_CONSOLE -DNO_STRICT -DHAVE_DES_FCRYPT -DUSE_SITECUSTOMIZE -DPERL_IMPLICIT_CONTEXT -DPERL_IMPLICIT_SYS -DUSE_PERLIO -D_USE_32BIT_TIME_T -DPERL_MSVCRT_READFIX',
    optimize='-MD -Zi -DNDEBUG -O1',
    cppflags='-DWIN32'
    ccversion='12.00.8804', gccversion='', gccosandvers=''
    intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
    d_longlong=undef, longlongsize=8, d_longdbl=define, longdblsize=8
    ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='__int64', lseeksize=8
    alignbytes=8, prototype=define
  Linker and Libraries:
    ld='link', ldflags ='-nologo -nodefaultlib -debug -opt:ref,icf  -libpath:"C:\Program Files (x86)\Perl\lib\CORE"  -machine:x86'
    libpth=\lib
    libs=  oldnames.lib kernel32.lib user32.lib gdi32.lib winspool.lib  comdlg32.lib advapi32.lib shell32.lib ole32.lib oleaut32.lib  netapi32.lib uuid.lib ws2_32.lib mpr.lib winmm.lib  version.lib odbc32.lib odbccp32.lib comctl32.lib msvcrt.lib
    perllibs=  oldnames.lib kernel32.lib user32.lib gdi32.lib winspool.lib  comdlg32.lib advapi32.lib shell32.lib ole32.lib oleaut32.lib  netapi32.lib uuid.lib ws2_32.lib mpr.lib winmm.lib  version.lib odbc32.lib odbccp32.lib comctl32.lib msvcrt.lib
    libc=msvcrt.lib, so=dll, useshrplib=true, libperl=perl512.lib
    gnulibc_version=''
  Dynamic Linking:
    dlsrc=dl_win32.xs, dlext=dll, d_dlsymun=undef, ccdlflags=' '
    cccdlflags=' ', lddlflags='-dll -nologo -nodefaultlib -debug -opt:ref,icf  -libpath:"C:\Program Files (x86)\Perl\lib\CORE"  -machine:x86'

Locally applied patches:
    ACTIVEPERL_LOCAL_PATCHES_ENTRY
    1fd8fa4 Add Wolfram Humann to AUTHORS
    f120055 make string-append on win32 100 times faster
    a2a8d15 Define _USE_32BIT_TIME_T for VC6 and VC7
    007cfe1 Don't pretend to support really old VC++ compilers
    6d8f7c9 Get rid of obsolete PerlCRT.dll support
    d956618 Make Term::ReadLine::findConsole fall back to STDIN if /dev/tty can't be opened
    321e50c Escape patch strings before embedding them in patchlevel.h

---
@INC for perl 5.12.2:
    C:/Program Files (x86)/Perl/site/lib
    C:/Program Files (x86)/Perl/lib
    .

---
Environment for perl 5.12.2:
    HOME (unset)
    LANG (unset)
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=C:\ProgramData\Oracle\Java\javapath;C:\Oracle\product\11.2.0\client_1\bin;C:\Program Files (x86)\Perl\site\bin;C:\Program Files (x86)\Perl\bin;C:\windows\system32;C:\windows;C:\windows\System32\Wbem;C:\windows\System32\WindowsPowerShell\v1.0\;C:\Program Files (x86)\PKWARE\pkzipc;C:\Program Files (x86)\Microsoft Application Virtualization Client;C:\Program Files (x86)\SSH Communications Security\SSH Tectia\SSH Tectia AUX;C:\Program Files (x86)\SSH Communications Security\SSH Tectia\SSH Tectia AUX\Support binaries;C:\Program Files (x86)\SSH Communications Security\SSH Tectia\SSH Tectia Broker;C:\Program Files (x86)\SSH Communications Security\SSH Tectia\SSH Tectia Client;C:\windows\System32\WindowsPowerShell\v1.0\;C:\Program Files\1E\NomadBranch\
    PERL_BADLANG (unset)
    SHELL (unset)

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