From: Paul Brannan <paul@...>
Date: 2002-04-10T22:57:25+09:00
Subject: Re: C++ extensions, garbage collection, Ruby and SWIG

On Wed, Apr 10, 2002 at 10:30:29AM +0900, Phil Tomson wrote:
> That actually sounds like good advice, however the library I want to 
> 'swig' already has 'automated garbage collection' as a feature.  Will this 
> cause trouble?  Are there ways to work around the problems that might 
> be caused by this?

I don't know how swig will deal with languages that do not have their
own garbage collection, but for Ruby, swig uses Ruby's built-in garbage
collection (but it abstracts all this away so you don't have to think
about it much).

The only cases I have found where garbage collection was an issue with
swig were:

  1) I needed to callback into Ruby code, so I passed in a VALUE
     directly to my C++ code.  I stored a reference to this VALUE, so I
     had to mark it.
  2) I have some odd typemaps that need to be aware of Ruby's GC.  I
     think that most typemaps do not (it has to do with wrapping CORBA
     objects and adding/removing references; the code is buried
     somewhere, so please don't ask for an example).
  3) When writing my exception handler (using swig's %except), I needed
     to know that Ruby uses longjmp for exceptions, and that this would
     interfere with cleanup of any C++ exceptions.  I can use the Ruby
     GC, though, to ensure proper cleanup (or I can do this in C++ with
     an extra try/catch).

Perhaps Lyle can come up with a couple more cases.

Paul