Trace what prevents an object from being GC'd?

Dan Rathbun

But I did not show() the dialog in the previous test, so:

dlg=MyDialog.new('Test')
>> #<MyDialog;0x61d2f30>
dlg.show
>> true
# empty dialog with title 'Test' is displayed,
# .. and I close it manually.
ObjectSpace.each_object(UI;;WebDialog) {}
>> 2
ObjectSpace.each_object(MyDialog) {}
>> 2
dlg=nil
>> nil
ObjectSpace.each_object(MyDialog) {}
>> 2
ObjectSpace.each_object(UI;;WebDialog) {}
>> 2
GC.start
>> nil
ObjectSpace.each_object(UI;;WebDialog) {}
>> 0
ObjectSpace.each_object(MyDialog) {}
>> 0

Dan Rathbun

Are you testing on PC (v1.8.6-p287) or Mac (v1.8.5-p0) ??

I guess I should say that I'm running:
RUBY_VERSION 1.8.7 RUBY_PATCHLEVEL 299

.. get I set it for a test and forgot to set it back.

Dan Rathbun

@ThomThom...

look at this example:
https://gist.github.com/355820

A the bottom he determines that there is a finalizer that is holding a ref to the instance, and therefor the reason why the instance is not getting GC'd.

I know you were trying to use a finalizer to cleanup a temp file.. likely that's the culprit.

thomthom

@dan rathbun said:

@ThomThom...

look at this example:
https://gist.github.com/355820

A the bottom he determines that there is a finalizer that is holding a ref to the instance, and therefor the reason why the instance is not getting GC'd.

I know you were trying to use a finalizer to cleanup a temp file.. likely that's the culprit.

Not in this case. I'm testing on SU8, default Ruby. I've used finalizer, but it only triggers under OSX. And I've read the gotchas about finalizers not GC'ing - and implemented it so it doesn't hold a reference.

However, I think I'm somehow creating a reference somewhere... I just can't track it down...

thomthom

It seems to be due to using self.add_action_callback within the initialize method of the subclass.

<span class="syntaxdefault">class WC </span><span class="syntaxkeyword"><</span><span class="syntaxdefault"> UI</span><span class="syntaxkeyword">;;</span><span class="syntaxdefault">WebDialog</span><span class="syntaxkeyword">;</span><span class="syntaxdefault"> def initialize</span><span class="syntaxkeyword">(*</span><span class="syntaxdefault">args</span><span class="syntaxkeyword">);</span><span class="syntaxdefault"> super</span><span class="syntaxkeyword">;</span><span class="syntaxdefault"> self</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">add_action_callback</span><span class="syntaxkeyword">(</span><span class="syntaxstring">'test'</span><span class="syntaxkeyword">)</span><span class="syntaxdefault"> </span><span class="syntaxkeyword">{</span><span class="syntaxdefault"> </span><span class="syntaxkeyword">|</span><span class="syntaxdefault">diag</span><span class="syntaxkeyword">,</span><span class="syntaxdefault">param</span><span class="syntaxkeyword">|</span><span class="syntaxdefault"> puts diag</span><span class="syntaxkeyword">,</span><span class="syntaxdefault"> param </span><span class="syntaxkeyword">};</span><span class="syntaxdefault">end</span><span class="syntaxkeyword">;</span><span class="syntaxdefault">end</span><span class="syntaxkeyword">;<br /></span><span class="syntaxdefault">nil<br /><br />ObjectSpace</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">each_object</span><span class="syntaxkeyword">(</span><span class="syntaxdefault">WC</span><span class="syntaxkeyword">){}<br /></span><span class="syntaxdefault">0<br /><br />x</span><span class="syntaxkeyword">=</span><span class="syntaxdefault">WC</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">new </span><span class="syntaxstring">'test'<br /></span><span class="syntaxcomment">#<WC;0x18dc1000><br /><br /></span><span class="syntaxdefault">ObjectSpace</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">each_object</span><span class="syntaxkeyword">(</span><span class="syntaxdefault">WC</span><span class="syntaxkeyword">){}<br /></span><span class="syntaxdefault">2<br /><br />x</span><span class="syntaxkeyword">=</span><span class="syntaxdefault">nil<br />nil<br /><br />GC</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">start<br />nil<br /><br />ObjectSpace</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">each_object</span><span class="syntaxkeyword">(</span><span class="syntaxdefault">WC</span><span class="syntaxkeyword">){}<br /></span><span class="syntaxdefault">2<br /></span>

When I use add_action_callback outside initialize it does get GC'd.

<span class="syntaxdefault">ObjectSpace</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">each_object</span><span class="syntaxkeyword">(</span><span class="syntaxdefault">UI</span><span class="syntaxkeyword">;;</span><span class="syntaxdefault">WebDialog</span><span class="syntaxkeyword">){}<br /></span><span class="syntaxdefault">2<br /><br />wd</span><span class="syntaxkeyword">=</span><span class="syntaxdefault">UI</span><span class="syntaxkeyword">;;</span><span class="syntaxdefault">WebDialog</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">new </span><span class="syntaxstring">'test'<br /></span><span class="syntaxcomment">#<UI;;WebDialog;0x18f1a2a8><br /><br /></span><span class="syntaxdefault">ObjectSpace</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">each_object</span><span class="syntaxkeyword">(</span><span class="syntaxdefault">UI</span><span class="syntaxkeyword">;;</span><span class="syntaxdefault">WebDialog</span><span class="syntaxkeyword">){}<br /></span><span class="syntaxdefault">4<br /><br />wd</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">add_action_callback</span><span class="syntaxkeyword">(</span><span class="syntaxstring">'test'</span><span class="syntaxkeyword">)</span><span class="syntaxdefault"> </span><span class="syntaxkeyword">{</span><span class="syntaxdefault"> </span><span class="syntaxkeyword">|</span><span class="syntaxdefault">diag</span><span class="syntaxkeyword">,</span><span class="syntaxdefault">param</span><span class="syntaxkeyword">|</span><span class="syntaxdefault"> puts diag</span><span class="syntaxkeyword">,</span><span class="syntaxdefault"> param </span><span class="syntaxkeyword">}<br /></span><span class="syntaxdefault">true<br /><br />wd </span><span class="syntaxkeyword">=</span><span class="syntaxdefault"> nil<br />nil<br /><br />GC</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">start<br />nil<br /><br />ObjectSpace</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">each_object</span><span class="syntaxkeyword">(</span><span class="syntaxdefault">UI</span><span class="syntaxkeyword">;;</span><span class="syntaxdefault">WebDialog</span><span class="syntaxkeyword">){}<br /></span><span class="syntaxdefault">2<br /></span>

I don't understand why...

Dan Rathbun

@thomthom said:

It seems to be due to using self.add_action_callback within the initialize method of the subclass.

I don't understand why...

Oh.. that's an easy one: Because **self** IS a reference to THE instance.
So YOUR telling Ruby to keep 'literal' reference within the code.

You dont need that reference by the way.. because the initialize method ALWAYS gets executed WITHIN the newly created instance, just after the class constructor (usually new,) creates it.

So just remove the " self." from in front of ALL instance method calls made from within ANY of the object's instance methods.

Chris Fullmer

Interesting,

thomthom

I had a suspicion that might be it, and it's what I had planned to try next. But I still don't understand why. As self.add_action_callback is just calling a method, never is self being stored in any reference...

thomthom

Removing self. from add_action_callback made no difference.

thomthom

I finally nailed it. I created the procs for add_action_callback as class constants instead of creating blocks within the initialize method and that allowed the WebDialog to be GC'd.

Dan Rathbun

@unknownuser said:

(http://forums.sketchucation.com/viewtopic.php?f) of this topic":25oe0j3o]

Did you dispose of all Locals, Constants, instance vars, and perhaps maybe even Procs that are within your subclass?

That said... you should be able to have proc refs, if they are instance @refs because they are likely to have refs inside them that ref instance objects.

If the class is a singleton (most WebDialogs are,) just limit the number of instances to 1, in the wrapping namespace, the same way you would for a tool instance.