From: Joel VanderWerf <vjoel@...>
Date: 2006-10-27T05:05:21+09:00
Subject: Re: debugging memory use and GC

Rick DeNatale wrote:
> On 10/25/06, snacktime <snacktime@gmail.com> wrote:
>> What is a good way to find out what objects are not being GC'd ?  I am
>> seeing a strange pattern I can't figure out.  The app is handling
>> large files and will use up to 150mb or so of memory and then when I
>> call GC.start it goes back down to around 8mb.  But after a few cycles
>> memory stops being reclaimed.
> 
> Of course, what you really want to know is not just what's not getting
> GCed but WHY.
> 
> This can be a difficult problem.  You really want to find the
> reference paths from root objects.
> 
> Some GC languages like Smalltalk have methods in object to get a list
> of everything which references it. I haven't seen such a facility in
> Ruby.  Then the problem with this is that calling this method
> generates additional references to the objects referencing the object
> etc.  This kind of heisenberg effect makes building a tool to find
> reference paths difficult.
> 

I wrote a patch for ruby 1.6/1.7 that would search for all ways of 
reaching an object from root objects in objectspace:

http://redshift.sourceforge.net/debugging-GC/

Usage info at:

http://redshift.sourceforge.net/debugging-GC/gc-patch.txt

Nobu updated it for CVS as of 12 Aug 2005:

http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/151854

I've found this to be useful only once or twice, but in those rare cases 
it can be very helpful...

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407