Mouse with threads does not work well Perl 5.21.2

[syohex]

This causes test failure of Text::Xslate.

Here is test program.

#!perl
package Foo;
use Mouse;

has syntax => (
    is      => 'rw',
    isa     => 'Str',
    default => 'Koron',
);

package main;
use strict;
use warnings;
use threads;

use Test::More;

my $foo = Foo->new;
is $foo->syntax, "Koron";

threads->create(sub{
    is $foo->syntax, "Koron";
})->join();

done_testing;

The test is failed with Perl 5.21.2

% perl -V
Summary of my perl5 (revision 5 version 21 subversion 2) configuration:

  Platform:
    osname=linux, osvers=3.13.0-32-generic, archname=x86_64-linux-thread-multi
    uname='linux vox 3.13.0-32-generic #57-ubuntu smp tue jul 15 03:51:08 utc 2014 x86_64 x86_64 x86_64 gnulinux '
    config_args='-Dprefix=/home/syohei/.plenv/versions/5.21.2-debug -de -Dusedevel -DDEBUGGING=-g -Dusethreads -A'eval:scriptdir=/home/syohei/.plenv/versions/5.21.2-debug/bin''
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=define, usemultiplicity=define
    use64bitint=define, use64bitall=define, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -fwrapv -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 -fwrapv -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
    ccversion='', gccversion='4.8.2', 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 =' -fstack-protector -L/usr/local/lib'
    libpth=/usr/local/lib /usr/lib/gcc/x86_64-linux-gnu/4.8/include-fixed /usr/include/x86_64-linux-gnu /usr/lib /lib/x86_64-linux-gnu /lib/../lib /usr/lib/x86_64-linux-gnu /usr/lib/../lib /lib
    libs=-lnsl -ldl -lm -lcrypt -lutil -lpthread -lc
    perllibs=-lnsl -ldl -lm -lcrypt -lutil -lpthread -lc
    libc=libc-2.19.so, so=so, useshrplib=false, libperl=libperl.a
    gnulibc_version='2.19'
  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'


Characteristics of this binary (from libperl): 
  Compile-time options: HAS_TIMES MULTIPLICITY PERLIO_LAYERS
                        PERL_DONT_CREATE_GVSV
                        PERL_HASH_FUNC_ONE_AT_A_TIME_HARD
                        PERL_IMPLICIT_CONTEXT PERL_MALLOC_WRAP
                        PERL_NEW_COPY_ON_WRITE PERL_PRESERVE_IVUV
                        PERL_USE_DEVEL USE_64_BIT_ALL USE_64_BIT_INT
                        USE_ITHREADS USE_LARGE_FILES USE_LOCALE
                        USE_LOCALE_COLLATE USE_LOCALE_CTYPE
                        USE_LOCALE_NUMERIC USE_LOCALE_TIME USE_PERLIO
                        USE_PERL_ATOF USE_REENTRANT_API
  Built under linux
  Compiled at Aug  5 2014 11:54:58
  %ENV:
    PERLDOC_PAGER="less -R"
  @INC:
    /home/syohei/.plenv/versions/5.21.2-debug/lib/perl5/site_perl/5.21.2/x86_64-linux-thread-multi
    /home/syohei/.plenv/versions/5.21.2-debug/lib/perl5/site_perl/5.21.2
    /home/syohei/.plenv/versions/5.21.2-debug/lib/perl5/5.21.2/x86_64-linux-thread-multi
    /home/syohei/.plenv/versions/5.21.2-debug/lib/perl5/5.21.2
    .
%  perl test.pl
ok 1
not ok 2
#   Failed test at test.pl line 22.
#          got: undef
#     expected: 'Koron'
1..2
# Looks like you failed 1 test of 2.

But the test is passed before Perl 5.21.2.

syohei@vox:% perl -V
Summary of my perl5 (revision 5 version 21 subversion 1) configuration:

  Platform:
    osname=linux, osvers=3.13.0-32-generic, archname=x86_64-linux-thread-multi
    uname='linux vox 3.13.0-32-generic #57-ubuntu smp tue jul 15 03:51:08 utc 2014 x86_64 x86_64 x86_64 gnulinux '
    config_args='-Dprefix=/home/syohei/.plenv/versions/5.21.1-debug -de -Dusedevel -DDEBUGGING=-g -Dusethreads -A'eval:scriptdir=/home/syohei/.plenv/versions/5.21.1-debug/bin''
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=define, usemultiplicity=define
    use64bitint=define, use64bitall=define, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -fwrapv -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 -fwrapv -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
    ccversion='', gccversion='4.8.2', 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 =' -fstack-protector -L/usr/local/lib'
    libpth=/usr/local/lib /usr/lib/gcc/x86_64-linux-gnu/4.8/include-fixed /usr/include/x86_64-linux-gnu /usr/lib /lib/x86_64-linux-gnu /lib/../lib /usr/lib/x86_64-linux-gnu /usr/lib/../lib /lib
    libs=-lnsl -ldl -lm -lcrypt -lutil -lpthread -lc
    perllibs=-lnsl -ldl -lm -lcrypt -lutil -lpthread -lc
    libc=libc-2.19.so, so=so, useshrplib=false, libperl=libperl.a
    gnulibc_version='2.19'
  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'


Characteristics of this binary (from libperl): 
  Compile-time options: HAS_TIMES MULTIPLICITY PERLIO_LAYERS
                        PERL_DONT_CREATE_GVSV
                        PERL_HASH_FUNC_ONE_AT_A_TIME_HARD
                        PERL_IMPLICIT_CONTEXT PERL_MALLOC_WRAP
                        PERL_NEW_COPY_ON_WRITE PERL_PRESERVE_IVUV
                        PERL_USE_DEVEL USE_64_BIT_ALL USE_64_BIT_INT
                        USE_ITHREADS USE_LARGE_FILES USE_LOCALE
                        USE_LOCALE_COLLATE USE_LOCALE_CTYPE
                        USE_LOCALE_NUMERIC USE_PERLIO USE_PERL_ATOF
                        USE_REENTRANT_API
  Built under linux
  Compiled at Aug  5 2014 12:55:02
  %ENV:
    PERLDOC_PAGER="less -R"
  @INC:
    /home/syohei/.plenv/versions/5.21.1-debug/lib/perl5/site_perl/5.21.1/x86_64-linux-thread-multi
    /home/syohei/.plenv/versions/5.21.1-debug/lib/perl5/site_perl/5.21.1
    /home/syohei/.plenv/versions/5.21.1-debug/lib/perl5/5.21.1/x86_64-linux-thread-multi
    /home/syohei/.plenv/versions/5.21.1-debug/lib/perl5/5.21.1
    .
% perl test.pl
ok 1
ok 2
1..2

Is this Perl issue or threads module ?

[syohex]

Perl 5.21.3 also fails this test.

[iabyn]

It's a thread safefy issue in Mouse. It has always had the potential for failure, but is more noticable in 5.21.2 onwards due to a new optimisation for looking up constant hash keys (just the HEK address is compared in the hash bucket entries, not the actual key string).

Mouse accessor XS subs have the constant key attached as magic to the CV, but also sets
CvXSUBANY(xsub).any_ptr to the mg pointer as a shortcut. When a thread is cloned, the magic
is cloned, but any_ptr continues pointing to the magic struct contained in the parent thread.
This is bad generally (e.g. the parent thread might exit before the child thread, leaving any_ptr
pointing at garbage), but specifically, the HEK embedded in the PVX field of the constant key SV
points to the shared hek of the parent thread, so simple HEK pointer comparisons no longer work.

[syohex]

Thanks for information.

[gfx]

This issue is not reproduced in perl 5.21.8.

[gfx]

WTF. This is sometimes reproduced.