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Hi Brent,

>>From your description below, I believe the fundamental problem might that
> the XML document "nodes" in the Node::Set are not Ruby objects.  Because
> of this, the garbage collector cannot see that XML::Node:Set has a
> dependency
> on the parent XML::Document.

Correct.

> It would probably be sufficient to add a pointer to the base of the
> parent XML::Document to
> the XML::Node::Set being returned by Document#find, even if this object
> reference
> were not otherwise necessary.   Having the object reference in the
> XML::Node::Set
> should prevent the garbage collector from freeing an XML::Document
> before any XML::Node::Set
> referring to it.

No, that's not the issue.  The XML::Node::Set object already has a mark 
function that tells the GC that it is dependent on the document.

The issue is that at shutdown, Ruby calls free functions in an 
undetermined order.  Doesn't matter what object graphs have been set up 
(at least that is how I interpret Nobu's reply:

http://blade.nagaokaut.ac.jp/cgi-bin/vframe.rb/ruby/ruby-core/17745?17500-17776+split-mode-vertical

> 
> Anyway, to fix this "the ruby way", think in terms of a the Ruby object
> dependency
> graph.  Pointers to anything that is not wrapped up as a Ruby object
> will not be
> respected as a dependency by the conservative Ruby garbage collector.

The only fix I see is the XML::Node::Set to register itself with the 
XML::Document (this is in C code).  Then when document_free gets called, 
the document checks to see if any XML::Node::Sets are about, and calls 
their free function.  Of course, that has to be noted by the 
XML::Node::Sets because Ruby is going to come along in another 
millisecond calling its free function again.  All fairly ugly.

Thus my hope that Ruby could do a mark/sweep before shutting down.  But 
I'm sure that introduces its own issues (not too mention slowing down 
shutdown).

Thanks for your thoughts....

Charlie

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