From: Joel VanderWerf <vjoel@...>
Date: 2003-09-15T05:59:24+09:00
Subject: Re: Debugging garbage collection

Nathan Weston wrote:
> I have a Ruby program that seems to be leaking memory -- in the sense
> that objects which I think should be GCed aren't getting GCed (even if
> I call GC.start).
> Something must be keeping references to these objects, but I can't
> figure out what.
> 
> Are there any tools to debug this problem? Some way to watch the GC in
> operation, or to find references to a particular object (at runtime),
> would be helpful.

You can patch gc.c and variable.c to give some information. See

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

The patches there are for 1.6.7 and 1.7.2, unfortunately. I haven't had 
the need to update them.

What it gives you is a method you can call like:

   GC.reachability_paths(obj)

and it will return an array of arrays, each of which is a path starting 
from some root reference in the interpreter, and ending with an object 
that contains a reference to obj. The root references can be ruby 
objects or can be references on the stack or in globals, and those are 
reported in descriptive strings, like

   "frame <number>: <filename> line <number>"
   "Ruby global <varname>"
   "C global <varname>"