I am not convinced is that there is either a need for, or a benefit to, sharing objects between threads.

Ah! I think I see the confusion. The protections are needed even without sharing objects between threads (where changes to an object in one thread are visible in another). Just creating a new thread can break any previously created inside-out object. In any new thread, inside-out objects that use a memory address as the "index" to the inside-out properties will break as the memory address changes. The new thread is a completely separate copy of all the data structures of the original and thus all the refaddr's change. 

use threads;

sub dump {
  my $self = shift;
  print "name: ", $self->name(), "\n";
}

$obj = Some::InsideOut::Class->new( name => "Larry" );

my $thread = threads->create( \&dump, $obj );

$thread->join();

[download]

Without CLONE, $obj in the new thread won't point to the same data as in the original thread. CLONE gives an opportunity to fix up the data structures. Note -- this isn't using threads::shared; changes to $obj in the new thread wouldn't be seen in the original, but CLONE is still necessary.

I'm not even tackling threads::shared support -- though jdhedden claims to have it working in Object::InsideOut, so it's apparently possible.

I'm not sold on threads personally, but the real problem comes on Win32 where fork is really creating a thread. CLONE keeps Win32 fork safe for inside-out objects.

-xdg

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In reply to Re^7: Overriding bless for inside-out object safety by xdg
in thread Overriding bless for inside-out object safety by xdg

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