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LVALUE refs have an incorrect refcount #9084

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p5pRT opened this issue Oct 27, 2007 · 3 comments
Closed

LVALUE refs have an incorrect refcount #9084

p5pRT opened this issue Oct 27, 2007 · 3 comments

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@p5pRT
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@p5pRT p5pRT commented Oct 27, 2007

Migrated from rt.perl.org#46943 (status was 'resolved')

Searchable as RT46943$

@p5pRT
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@p5pRT p5pRT commented Oct 27, 2007

From @cpansprout

I don't seem to be able to weaken LVALUE refs​:
$ perl -MScalar​::Util=weaken -le '$_ = \substr$y,0; print; weaken $_;
print'
LVALUE(0x1801d88)
LVALUE(0x1801d88)

(Although 'isweak' claims it's weak.)

But if I execute the same compiled code more than once​:
$ perl -MScalar​::Util=weaken -le '$x = \substr$y,0 for 1..2; print
$x; weaken $x; print $x'
LVALUE(0x1801d4c)
<blank line>

It turns out the the first one has the wrong refcount​:
$ perl -le 'for (1..5){ push @​@​, \substr my $y,0; print
Internals​::SvREFCNT(${$@​[-1]}), " $@​[-1]" }'
2 LVALUE(0x1801dd0)
1 LVALUE(0x1801440)
1 LVALUE(0x1801e30)
1 LVALUE(0x1801e54)
1 LVALUE(0x1801e78)

(Without pushing it onto a var outside the block, it reuses the
reference,
alternating between two of them​:)
$ perl -le 'for (1..5){ $x = \substr my $y,0; print
Internals​::SvREFCNT($$x), " $x" }'
SvREFCNT($$x), " $x" }'
2 LVALUE(0x1801dd0)
1 LVALUE(0x180129c)
2 LVALUE(0x1801dd0)
1 LVALUE(0x180129c)
2 LVALUE(0x1801dd0)

If I weaken it, it forces it to use the same one again next time​:
$ perl -MScalar​::Util=weaken -le 'for (1..5){ push @​@​, \substr my $y,
0; print Internals​::SvREFCNT(${$@​[-1]}), " $@​[-1]" ; weaken $@​[-1] }'
2 LVALUE(0x1801db8)
2 LVALUE(0x1801db8)
2 LVALUE(0x1801db8)
2 LVALUE(0x1801db8)
2 LVALUE(0x1801db8)
$ perl -MScalar​::Util=weaken -le 'for (1..5){ push @​@​, \substr my $y,
0; print Internals​::SvREFCNT(${$@​[-1]}), " $@​[-1]" ; weaken $@​[-1] if
$_ %2}'
2 LVALUE(0x1801db8)
2 LVALUE(0x1801db8)
1 LVALUE(0x1801440)
1 LVALUE(0x1801440)
1 LVALUE(0x1818e78)

This occurs also in perl 5.8.8.

I hope that's enough information to help solve the problem. I
encountered the same thing with 'vec', but I haven't looked into it
in detail. (I wonder what pos() does.)

Father Chrysostomos


Flags​:
  category=core
  severity=low


This perlbug was built using Perl 5.10.0 - Mon Sep 24 10​:10​:11 PDT 2007
It is being executed now by Perl 5.10.0 - Sat Oct 6 16​:48​:24 PDT 2007.

Site configuration information for perl 5.10.0​:

Configured by neo at Sat Oct 6 16​:48​:24 PDT 2007.

Summary of my perl5 (revision 5 version 10 subversion 0 patch 32056)
configuration​:
  Platform​:
  osname=darwin, osvers=8.8.0, archname=darwin-2level
  uname='darwin treebeard.local 8.8.0 darwin kernel version 8.8.0​:
fri sep 8 17​:18​:57 pdt 2006; root​:xnu-792.12.6.obj~1release_ppc power
macintosh powerpc '
  config_args='-de'
  hint=recommended, useposix=true, d_sigaction=define
  useithreads=undef, usemultiplicity=undef
  useperlio=define, d_sfio=undef, uselargefiles=define,
usesocks=undef
  use64bitint=undef, use64bitall=undef, uselongdouble=undef
  usemymalloc=n, bincompat5005=undef
  Compiler​:
  cc='cc', ccflags ='-fno-common -DPERL_DARWIN -no-cpp-precomp -
fno-strict-aliasing -pipe -I/usr/local/include',
  optimize='-O3',
  cppflags='-no-cpp-precomp -fno-common -DPERL_DARWIN -no-cpp-
precomp -fno-strict-aliasing -pipe -I/usr/local/include'
  ccversion='', gccversion='4.0.0 20041026 (Apple Computer, Inc.
build 4061)', gccosandvers='darwin8'
  intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=4321
  d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16
  ivtype='long', ivsize=4, nvtype='double', nvsize=8,
Off_t='off_t', lseeksize=8
  alignbytes=8, prototype=define
  Linker and Libraries​:
  ld='env MACOSX_DEPLOYMENT_TARGET=10.3 cc', ldflags =' -L/usr/
local/lib'
  libpth=/usr/local/lib /usr/lib
  libs=-ldbm -ldl -lm -lc
  perllibs=-ldl -lm -lc
  libc=/usr/lib/libc.dylib, so=dylib, useshrplib=false,
libperl=libperl.a
  gnulibc_version=''
  Dynamic Linking​:
  dlsrc=dl_dlopen.xs, dlext=bundle, d_dlsymun=undef, ccdlflags=' '
  cccdlflags=' ', lddlflags=' -bundle -undefined dynamic_lookup -L/
usr/local/lib'

Locally applied patches​:
  DEVEL


@​INC for perl 5.10.0​:
  /usr/local/lib/perl5/5.9.5/darwin-2level
  /usr/local/lib/perl5/5.9.5
  /usr/local/lib/perl5/site_perl/5.9.5/darwin-2level
  /usr/local/lib/perl5/site_perl/5.9.5
  .


Environment for perl 5.10.0​:
  DYLD_LIBRARY_PATH (unset)
  HOME=/Users/neo
  LANG (unset)
  LANGUAGE (unset)
  LD_LIBRARY_PATH (unset)
  LOGDIR (unset)
  PATH=/bin​:/sbin​:/usr/bin​:/usr/sbin​:/usr/TeX/bin/powerpc-
darwin6.8​:/usr/local/bin
  PERL_BADLANG (unset)
  SHELL=/bin/bash

@p5pRT
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@p5pRT p5pRT commented Apr 6, 2011

From @cpansprout

This appears to have been resolved by commit 2154eca, so it was
presumably related to, or the same bug as, #67838.

@p5pRT
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@p5pRT p5pRT commented Apr 6, 2011

@cpansprout - Status changed from 'new' to 'resolved'

@p5pRT p5pRT closed this Apr 6, 2011
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