Re: Breaking reference cycles ( continued from ages ago )

[muppet <scott asofyet org>]

On Dec 15, 2005, at 6:32 PM, Daniel Kasak wrote:

> However in Gtk2::Ex::Datasheet::DBI, this doesn't work. This could  
> very well be because I'm using some custom cell renderers that set  
> up their own signal handlers, eg:
>
> $editable -> signal_connect(key_press_event => sub { ... some  
> stuff ...});
>
> Do I have to clean this stuff up as well? The cell renderers aren't  
> set up in an OO way ( ie they can't see $self that the rest of  
> Gtk2::Ex::Datasheet::DBI sees ). This will make my above approach  
> of stuffing them in an array and disconnecting them later more  
> complicated.

Not quite sure i follow exactly where your cycles are occurring, but  
there are a few different things you can do:

- Try to avoid using an external reference to an instance in a  
closure; use the signal handler's arguments as much as possible.  E.g.,

      # avoid this -- it traps the external $button in the closure  
for the
      # signal handler, making $button refer to itself.
      $button->signal_connect (clicked => sub {
               $button->foo();
      });

      # do this instead:
      $button->signal_connect (clicked => sub {
              my $button = (@_);
              $button->foo();
      });


- GtkObject's destroy signal exists so that you can break reference  
cycles explicitly; try breaking relevant links there.

    $widget_with_lots_of_links->signal_connect (destroy => sub {
        my $self = shift;
        delete $self->{other_widget_1};
        delete $self->{other_widget_2};
        delete $self->{tree_model};
        # usually there's only one or two key things to break here.
    });


- Many reference cycles occur because object A owns object B, but  
object B has to have a backreference to A in order to update A on  
some change in B.  This is a perfect reason to create a new signal  
and decouple B from A.  Not only does it clean up some of your  
reference cycles, the reduced coupling makes the program a bit easier  
to maintain.


--
I don't like... this game... when there's cannons... being shot... at  
me.
  -- Elysse