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[perl #47045] CLONE_SKIP doesn't result in undef copies

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From:
Olly Betts
Date:
October 31, 2007 01:54
Subject:
[perl #47045] CLONE_SKIP doesn't result in undef copies
Message ID:
rt-3.6.HEAD-24634-1193798427-650.47045-75-0@perl.org
# New Ticket Created by  Olly Betts 
# Please include the string:  [perl #47045]
# in the subject line of all future correspondence about this issue. 
# <URL: http://rt.perl.org/rt3/Ticket/Display.html?id=47045 >


This is a bug report for perl from olly@survex.com,
generated with the help of perlbug 1.35 running under perl v5.8.8.


-----------------------------------------------------------------
[Please enter your report here]

"perldoc perlmod" says:

    Like "CLONE", "CLONE_SKIP" is called once per package; however, it is
    called just before cloning starts, and in the context of the parent
    thread. If it returns a true value, then no objects of that class will
    be cloned; or rather, they will be copied as unblessed, undef values.

But in my tests, the copies are unblessed, but aren't undef.  Here's a
simple example:

## Class.pm:

package Class;

use strict;

sub CLONE_SKIP { 1 }

sub new { bless {} }

1;

## cloneskip.pl:

#!/usr/bin/perl -W
use strict;
use Class;
use threads;

my $obj = Class->new();

sub check_obj {
    my $where = shift;
    print "$where: ref(\$obj) = ".ref($obj)."\n";
    print "$where: defined(\$obj) = ".defined($obj)."\n\n";
}

check_obj("main");
my $thread1 = threads->create(sub { check_obj("thread"); 1; } );
$thread1->join();
check_obj("main");

Output from "perl clone_skip.pl":

main: ref($obj) = Class
main: defined($obj) = 1

thread: ref($obj) = SCALAR
thread: defined($obj) = 1

main: ref($obj) = Class
main: defined($obj) = 1

The documentation leads me to expect the third and fourth non-blank lines
should be:

thread: ref($obj) = 
thread: defined($obj) = 

as that is what I get if I change cloneskip.pl to do this:

my $thread1 = threads->create(sub { $obj = undef; check_obj("thread"); 1; } );

The documented behaviour seems sensible, so I think the bug here is in the
implementation rather than the documentation.

Cheers,
    Olly

[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
    category=core
    severity=low
---
Site configuration information for perl v5.8.8:

Configured by Debian Project at Fri Sep 28 22:34:35 GMT 2007.

Summary of my perl5 (revision 5 version 8 subversion 8) configuration:
  Platform:
    osname=linux, osvers=2.6.15.7, archname=x86_64-linux-gnu-thread-multi
    uname='linux yellow 2.6.15.7 #1 smp sun sep 23 13:51:52 utc 2007 x86_64 gnulinux '
    config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN -Dcccdlflags=-fPIC -Darchname=x86_64-linux-gnu -Dprefix=/usr -Dprivlib=/usr/share/perl/5.8 -Darchlib=/usr/lib/perl/5.8 -Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5 -Dvendorarch=/usr/lib/perl5 -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl/5.8.8 -Dsitearch=/usr/local/lib/perl/5.8.8 -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 -Uusesfio -Uusenm -Duseshrplib -Dlibperl=libperl.so.5.8.8 -Dd_dosuid -des'
    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=define uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS -DDEBIAN -fno-strict-aliasing -pipe -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-O2',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS -DDEBIAN -fno-strict-aliasing -pipe -I/usr/local/include'
    ccversion='', gccversion='4.1.3 20070831 (prerelease) (Ubuntu 4.1.2-16ubuntu1)', gccosandvers=''
    intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16
    ivtype='long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
    alignbytes=8, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -L/usr/local/lib'
    libpth=/usr/local/lib /lib /usr/lib
    libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt
    perllibs=-ldl -lm -lpthread -lc -lcrypt
    libc=/lib/libc-2.6.1.so, so=so, useshrplib=true, libperl=libperl.so.5.8.8
    gnulibc_version='2.6.1'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -L/usr/local/lib'

Locally applied patches:
    

---
@INC for perl v5.8.8:
    /etc/perl
    /usr/local/lib/perl/5.8.8
    /usr/local/share/perl/5.8.8
    /usr/lib/perl5
    /usr/share/perl5
    /usr/lib/perl/5.8
    /usr/share/perl/5.8
    /usr/local/lib/site_perl
    /usr/local/lib/perl/5.8.7
    /usr/local/share/perl/5.8.7
    /usr/local/lib/perl/5.8.4
    /usr/local/share/perl/5.8.4
    .

---
Environment for perl v5.8.8:
    HOME=/home/olly
    LANG=en_GB.UTF-8
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/bin/X11:/usr/games
    PERL_BADLANG (unset)
    SHELL=/bin/bash


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