Hi peoples,

I thought my script which uses either ithreads, 5005threads or none, depending on environment, was working fine and dandy.. Until I noticed that I should have been sharing some objects (plugins) between the threads, and I wasnt, and thus the fun started.

According to the threads::shared docs:

"bless" is not supported on shared references. In the current version, "bless" will only bless the thread local reference and the blessing will not propagate to the other threads. This is expected to be implemented in a future version of Perl.
However, my tests show that this is not quite true. There are some strange things you can do, and more importantly, not do, with shared variables. It seems you can bless shared variables, for example, and the blessed object works fine in a thread.. You cant share a blessed object though, since whenever you share something, its contents get clobbered. These and other things might have been useful to put the threads::shared docs.. See test code below: 
#!/usr/bin/perl -w

use Data::Dumper;
use Storable 'freeze', 'thaw';
use threads;
use threads::shared;

use Net::Ping;

# Create hashref, set a value
my $hashref = {};
$hashref->{'mine'} = 12;

#share hashref - original value gone!
share($hashref);
print "Shared hashref: ", Dumper($hashref), "\n";

# Create object
my $ping = Net::Ping->new();
print "Object: ", Dumper($ping), "\n";

# Share object - values gone
share($ping);
print "Shared object (empty): ", Dumper($ping), "\n";

# Recreate (bless shared thing, works fine..)
$ping = Net::Ping->new();
print "Shared object (renewed): ", Dumper($ping), "\n";

# Create, share, then bless.. works..
my $newping = {};
share($newping);
$newping = Net::Ping->new();
print "Shared then bless: ", Dumper($newping), "\n";

# Use in another thread, just to check
my $thr = threads->create(\&ping_it);
#  Wait for ping to complete
$thr->join();

sub ping_it
{
    print "ping_it ", Dumper($ping);
    print "Ping localhost: ", ($ping->ping('localhost') ? "yes" : "no"
+), "\n";
    # Works!
}

# Put shared thingy in other shared thingy.. (I want(ed) a hash of obj
+ects..)

my $hashy = {};
share($hashy);

# $hashy->{'ping'} = $ping;
# print "Hash of obj: ", Dumper($hashy);
# Damn, doesnt work - Invalid value for shared scalar at ../threadtest
+.pl line 53.

my %hashy = ();
share(%hashy);

# $hashy{'ping'} = $ping;
# print "Hash of obj: ", Dumper(%hashy);
# Damn, doesnt work - Invalid value for shared scalar at ../threadtest
+.pl line 53.

# my $testping = Net::Ping->new();
# $hashy->{'ping'} = $testping;
# Can't do that either..

# $hashy->{'ping'} = freeze($ping);
# print "Hash of obj: ", Dumper(%hashy);
# Nope..

$hashy->{'ping'} = freeze(pingy->new());
print "Hash of obj: ", Dumper($hashy);
# hmm, works.. (but only if no globs or code-refs)
$thr = threads->create(\&test_me);
$thr->join();

sub test_me
{
    print Dumper(thaw($hashy->{'ping'}));
}

package pingy;
use Data::Dumper;

sub new
{
    # Create new pingy
    # Parameter: Class-Name/Reference, Properties
    my $class = shift;
    $class = ref($class) || $class;
    my $self = {'just' => 'testing'};
    bless($self, $class);

    print "Created: ", Dumper($self), "\n";
    return $self;
}

[download]
.. So, if I keep my modules free of code refs and globs, it seems I can cheat a little, use freeze/thaw, and actually share objects. Of course, no guarantee that this behaviour will work in the next version..

(All tests here done with 5.8.2, on linux)

Anyone know how, what, why and WTF?

C.

In reply to ithreads, shared variables.. by castaway

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