Help : Memory Leak Problem

[Alberto Rugnone]

Hello everybody,
In my office we are experiencing a very bad problem of memory leak. We
are developing an application with GWT based on MVP architecture.
Each widget is a MVP and each MVP is based on a own class named
DefaultWidgetPresenter. The applicaion has to create periodically new
Presenters (subclass of the first) and deletes periodically olders.
Anyway application memory grows up. Profiling the application with
developer tools provided by Chrome or Safari we registered that
Presenter keeps their number increasing slowly and
DefaultWidgetPresenter still growing up rapidly, and we don't
understand why? We checked if we deleted correctly the presenter and
sincerely I can't say "yes" because our probably no deep understanding
of GWT technology.
This is the application procedure in a nutshell
1) Application create a Presenter dynamically
2) Then it put its displays in a panel
3) Then after a certain time it creates a new Presenter
4) It clears the panel then add the new display.
... and so on

I expected old presenters are garbage collected in some way. In
addition I don't understand why we have difference between number of
Presenters instances and parents classes instance. I took
measurements also from chrome's task manager but I can't understand
the relation between profiling and that. In fact when I use profiling
the memory grows in a strange way probably because profiling
instrument the memory in some way.

There is some one that can help us and explain those behaviours? I am
wondering also if a key to understand the problem could be understand
how GWT implements inheritage and garbage collecting? ?

Thank you in advance for any help, this problem is very important.

Regards
Alberto

[Rob Coops]

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Hi Alberto,

Being an absolute novice in Java development but having spend many years supporting Java based applications and working with many other programming languages I would say there is a relatively simple reason for this behavior.

Usually the garbage collector will kill what ever is considered old enough (there are various stages in the objects life cycle but who cares right unused objects will die in the end). What you are doing to kill of the object in your code is not working as you expect it to. As long as there is a single reference to the object the garbage collector will see this as a object that's in use and thus will not remove it.

So what I understand form your post you are simply deleting the presenter from the panel. This works well for static things like a button or an image but as soon as you are talking a widget that is displaying data the data that you are displaying will still be updated in that widget as all you did is remove the widget from the display part of your program the code that is updating the widget will happily continue to work. I would say you will need to build a destroy method for your presenter that will remove all links to the data to be displayed. If you call this after you delete the presenter you should see the garbage collector clean it up nicely.

Now as I said before I am a complete novice in Java/GWT so I cannot make any promises about the sanity of my comments but from what I know from other languages and from supporting Java based systems for many years; the usual reason a garbage collector misses an object is because the developer forgot to remove all references to that object. ;-)

Regards,

Rob

[Alberto Rugnone]

Thank you Rob,
Maybe you are right. I will try to implement this destroy method and I
will get the results asap. Anyway while Presenter seems disappears (I
am talking about profiler on Chrome, then javascript objects), parent
classes don't and I expected or both Presenter and Parents stay life
or neither of them.

It is very strange, isn't it? Any clarification about that will be
very appreciated. Thanks


Best Regards

Alberto

On Jul 4, 6:16 pm, Rob Coops <rco...@gmail.com> wrote:
> On Mon, Jul 4, 2011 at 6:00 PM, Alberto Rugnone

> <arugnonechemi...@gmail.com>wrote:

[Marko Vuksanovic]

Do you have this problem in development or production mode?

[Alberto Rugnone]

In production. I didn't take measurements in development.

[Jmscavaleiro]

If you try the destroy implementation as suggested, it will be very
appreciated if you give a feedback about the result.

Thanks!