From: Rolando Abarca <funkaster@...>
Date: 2009-05-07T05:59:47+09:00
Subject: storing c pointers in ruby hash

Hi all,
I'm been banging my head on the keyboard the whole day trying to track  
a bug.
I have a embedded ruby (branch 1_9_1, checked out today) running on a  
Objective-C project (if anyone's interested, it's this project: http://github.com/funkaster/shinycocos/tree/master) 
.
The idea is to keep a reference to the ruby counterpart of the Obj-C  
object. Right now, I'm using a "global" hash table, defined as this:

	VALUE sc_object_hash = rb_hash_new();

The variable has been registered to the GC as suggested in the  
README.EXT:

	rb_global_variable(&sc_object_hash);

An objc object is associated to a new ruby object (the ruby version of  
the objc class) this way:

	node = [[SomeClass alloc] init];
	VALUE rb_obj = common_init(klass, nil, node, argc, argv, YES);
	common_link(node, rb_obj);

common_init is a function defined as follows:

VALUE common_init(VALUE klass, cocos_holder **ret_ptr, id object, int  
argc, VALUE *argv, BOOL release_on_free) {
	VALUE obj;
	cocos_holder *ptr;
	if (release_on_free)
		obj = Data_Make_Struct(klass, cocos_holder, 0, common_free, ptr);
	else
		obj = Data_Make_Struct(klass, cocos_holder, 0,  
common_free_no_release, ptr);
	ptr->_obj = object;
	rb_obj_call_init(obj, argc, argv);
	if (ret_ptr != nil)
		*ret_ptr = ptr;
	return obj;
}

and common_link is an inline function:

static inline void common_link(id obj1, VALUE obj2) {
	rb_hash_aset(sc_object_hash, INT2FIX((long)obj1), obj2);
}

Some times, the objc framework will call a method in the objc object.  
When this happens, I need to call the proper ruby method in the  
corresponding ruby object:

- (void)someMethodCalledByTheFramework {
	VALUE rb_obj = common_link_ref(self);
	rb_funcall(rb_obj, id_cb_on_enter, 0, 0);
}

common_link_ref is the counterpart of common_link (basically calls  
rb_hash_aref on the same hash)
The thing is, that the rb_obj is crashing the ruby interpreter. If I  
try to call any method on it (even inspect) I get a bad access error.  
It was working with a ruby 1.8 version, but now that I've ruby 1.9, it  
refuses to work... Any idea of what I could be doing wrong here?
Is there a better way to link a ruby object with a c pointer? I need  
to get the associated ruby object to a given objc object. Not the  
other way around (which is easy using Data_Get_Struct)... that's why  
I'm using a hash table.

thanks!
-- 
Rolando Abarca M.