From: Eric Hodel <drbrain@...7.net>
Date: 2011-02-09T09:21:04+09:00
Subject: Re: C extension: How to check if a VALUE is still alive (not being GC'ed)?

On Feb 8, 2011, at 3:18 PM, Iņaki Baz Castillo wrote:
> 2011/2/8 Eric Hodel <drbrain@segment7.net>:
>>> Yes, that's work: the resolver object contains a hash attribute in
>>> which queries are stored until completed.
>> 
>> Use a ruby hash and supply mark and GC callbacks to Data_Wrap_Struct so the GC will keep track of it.
> 
> Thanks, but I don't understand why I must use mark callback:
> 
> - My class uses Data_Wrap_Struct containing a xxx_free function to
> free the C structure when the object is GC'ed.
> 
> - An instance of my class contains an @hash attribute (which is set
> empty in initialize method).
> 
> - Such @hash is populted with some normal Ruby objects during runtime.
> Nothing special here.
> 
> - So when my instance is GC'ed, at some point Ruby will GC the @hash
> attribute and also the objects it contains.
> 
> Then... why do I need a mark callback? Maybe I miss something, however
> Itested my code under high load and doesn't seem to leak.
> Thanks a lot.

Since you use the instance variable you do not need the mark callback.  The mark callback is only required if you are storing ruby objects in a structure that hides them from ruby.