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Postings from November 2003
Scalar::Util::weaken() proposed to use in the conjunction with the CLONE
function to solve the problem of cloning non-perl objects suffers itself from
cloning.
Here is an example:
#/tmp/weaken2
package main;
use threads;
use Scalar::Util;
my $data = "a";
my $obj = \$data;
my $copy = $obj;
Scalar::Util::weaken($copy);
threads->new(sub { print "thread started\n";})->detach for (1..1);
sleep 1;
% perl-5.8.1-ithread /tmp/weaken2
thread started
Attempt to free unreferenced scalar SV 0x8154f74.
Oops, a weakened $copy was cloned too, but its guts are now messed
up. What scalar do you ask is unreferenced? It's the magic that was
added by weaken() and cloned during perl_clone, that perl complains about.
Here is a more complex program that proves that with Devel::Peek:
#/tmp/weaken
package Foo;
use strict;
use warnings;
use Scalar::Util;
use Devel::Peek;
my %objects;
sub new {
my $data = "a";
my $self = bless \$data, __PACKAGE__;
my $copy = $self;
Scalar::Util::weaken($copy);
$objects{"$self"} = $copy;
return $self;
}
sub DESTROY {
warn "DESTROY\n";
}
sub CLONE {
warn "CLONE is called";
for my $key ( keys %objects) {
my $self = delete $objects{$key};
Dump $self;
}
}
package main;
use threads;
my $obj = Foo->new;
threads->new(sub { print "thread started\n";})->detach for (1..1);
sleep 1;
% perl-5.8.1-ithread /tmp/weaken
CLONE is called at /tmp/weaken line 23.
SV = RV(0x8110b2c) at 0x815de1c
REFCNT = 1
FLAGS = (PADBUSY,PADMY,ROK)
RV = 0x8156e1c
SV = PVMG(0x8115e38) at 0x8156e1c
REFCNT = 2
FLAGS = (PADBUSY,PADMY,OBJECT,RMG,POK,pPOK)
IV = 0
NV = 0
PV = 0x8157860 "a"\0
CUR = 1
LEN = 2
MAGIC = 0x8157828
MG_VIRTUAL = &PL_vtbl_backref
MG_TYPE = PERL_MAGIC_backref(<)
MG_FLAGS = 0x02
REFCOUNTED
MG_OBJ = 0x8156e28
SV = PVAV(0x8153494) at 0x8156e28
REFCNT = 1
FLAGS = ()
IV = 0
NV = 0
ARRAY = 0x8157848
FILL = 0
MAX = 3
ARYLEN = 0x0
FLAGS = (REAL)
Elt No. 0
STASH = 0x8156d2c "Foo"
thread started
DESTROY
Attempt to free unreferenced scalar SV 0x8156e28 during global destruction.
DESTROY
As you can see SV 0x8156e28 is:
SV = PVAV(0x8153494) at 0x8156e28
REFCNT = 1
FLAGS = ()
IV = 0
NV = 0
ARRAY = 0x8157848
FILL = 0
MAX = 3
ARYLEN = 0x0
FLAGS = (REAL)
Elt No. 0
Any chance we can change perl to call Devel::Peek::Dump when producing:
Attempt to free unreferenced scalar SV 0x8154f74.
would save us a lot of time, trying to figure out what SV went lost.
__________________________________________________________________
Stas Bekman JAm_pH ------> Just Another mod_perl Hacker
http://stason.org/ mod_perl Guide ---> http://perl.apache.org
mailto:stas@stason.org http://use.perl.org http://apacheweek.com
http://modperlbook.org http://apache.org http://ticketmaster.com
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