Re: DESTROYing shared objects, finally

At 00:10 -0600 10/30/03, Mike Pomraning wrote:
>On Thu, 23 Oct 2003, Mike Pomraning wrote:
>
>>  [....] suggestions on how I might determine which DESTROY [of a shared,
>>  blessed ref] is the very last one?
>
>Sorry to reply to my own post, but here's how I've attempted to identify the
>last DESTROY of a shared object:
>
>   sub DESTROY {
>     return unless threads::shared::_refcnt($_[0]) == 1;
>     # if we're here, the shared object is going away for good.
>     # time to release system resources, call XS deallocators, etc.
>     }
>   }
>
>The only other approach I can think of is to do (ser|ted)ious inventorying via
>CLONE, DESTROY and constructors, or a wrapped bless.  (I did see the
>"[CAUTION] Thread-saving modules" not-a-bug thread from Jul 2002 before my
>previous post, but this is not quite the same.)

The "inventory" approach is the one that Thread::Pool uses.  But it 
may be simpler than you think:

There is a global that keeps the CLONE level:

our $cloned = 0;

Then this variable gets incremented with each clone:

sub CLONE { $cloned++ }


When an object gets created, it keeps the current cloned value with 
its information:

sub new {
      bless {cloned => $cloned},$_[0];
}


And then in DESTROY, you check whether they're still the same

sub DESTROY {
     return unless $_[0]->{'cloned'} == $cloned;
# other stuff
}


>Multiple destruction of non-shared objects makes sense to me, as each becomes
>a thread-local copy.  Multiple destruction of shared objects, however, does
>not (though I think I understand the mechanics of why it happens).  Am I
>looking at this issue the wrong way?

Maybe the above is already what you have, maybe it is simpler.  It 
works for Thread::Pool.

By the way, Thread::Pool also contains:

    return unless UNIVERSAL::isa( $_[0],__PACKAGE__ );  # ignore rogue DESTROYs

I'm not sure this is needed for 5.8.1 and above.  But it was 
definitely needed for 5.8.0.


Hope this helps.

Liz