From: "Sean O'Dell" <sean@...[REMOVE_THE_SPAM]>
Date: 2003-09-12T07:34:41+09:00
Subject: Re: GC - PLEASE  set me straight

Thomas Sondergaard wrote:

>>Hmm ... I'm confused about that statement.
> 
> 
> Well that wont do..
> 
> 
>>If the VALUE is a member of a class, then it's probably NOT on the
>>stack, so volatile won't help you there.  In this case, just use
>>rb_gc_register_address/rb_gc_unregister_address in your
>>constructor/destructor methods for your C++ class.
> 
> 
> 1) I am using rb_gc_register/unregister in my C++ wrapper.
> 
> 2) I have now added the volatile keyword in all the functions where I use an
> automatic variable.
> 
> 
> Here's the relevant bit of the C++ wrapper:
> 
> public __gc class Object : public DynamicLanguageSupport::IObject {
> public:
>     explicit Object(VALUE handle) {
>         _handle = ALLOC(VALUE);
>         *_handle = handle;
>         rb_gc_register_address(_handle);
>     }
> 
>     ~Object() {
>         rb_gc_unregister_address(_handle);
>         free(_handle);
>     }
> 
>     // stuff for invoking ruby methods from .net removed
> 
>     private:
>     VALUE __nogc *_handle;
> };
> 
> Does it look reasonable?

You don't need to ALLOC the VALUE though.  You can just make it a 
regular member of your class and register the &address of it.  When you 
get the &address of a member variable, it's true location in memory is 
given, and as far as I know that won't ever change during the lifetime 
of your object, so you can really just do it like this:

public __gc class Object : public DynamicLanguageSupport::IObject {
public:
     explicit Object(VALUE handle) {
         rb_gc_register_address(&_handle);
     }

     ~Object() {
         rb_gc_unregister_address(&_handle);
     }

     // stuff for invoking ruby methods from .net removed

     private:
     VALUE __nogc _handle;
};


Aside from that, it sounds like you have got the knack of it!

	Sean O'Dell