From: Charles Mills <cmills@...>
Date: 2004-07-31T00:19:16+09:00
Subject: Re: C ext: GC claiming objects early


On Jul 30, 2004, at 7:06 AM, Tilman Sauerbeck wrote:

> ts <decoux@moulon.inra.fr> [2004-07-30 15:43]:
>>>>>>> "T" == Tilman Sauerbeck <tilman@code-monkey.de> writes:
>>
>> T> "some_meth" will instantiate a new "Result" object. Using this 
>> Result
>> T> object, the caller can wait for the function to succeed, he can 
>> register
>> T> callbacks etc.
>>
>>  Well it's best if you post the *real* C code : it's easy to 
>> understand
>>  than this strange language, called english.
>
> Heh :)
>
> Here's the code for the method "some_meth", let's just call it
> "playback_playtime" now ;D
>
> static VALUE c_playback_playtime (VALUE self)
> {
> 	xmmsc_result_t *res;
>
> 	/* this just wraps Data_Get_Struct */
> 	GET_OBJ (self, xmmsc_connection_t *, xmms);
>
> 	res = xmmsc_playback_playtime (*xmms);
>
> 	/* now create a new Result object from the C struct */
> 	return TO_XMMS_CLIENT_RESULT (self, res);
> }
>
> VALUE TO_XMMS_CLIENT_RESULT (VALUE parent, xmmsc_result_t *res)
> {
> 	VALUE self;
> 	RbResult *rbres = NULL;
>
> 	if (!res)
> 		return Qnil;
>
> 	self = Data_Make_Struct (cResult, RbResult, c_mark, c_free, rbres);
> 	rbres->real = res;
> 	rbres->parent = parent;
> 	rbres->callback = Qnil;
You should show us c_mark and c_free
In extreme situations the above code it dangerous, here is a safer 
version:
<code>
	VALUE self;
	RbResult *rbres;

	if (!res)
		return Qnil;

	rbres = ALLOC(RbRecsult);
	rbres->real = res;
	rbres->parent = parent;
	rbres->callback = Qnil;
	self = Data_Wrap_Struct (cResult, c_mark, c_free, rbres);
</code>
>
> 	rb_obj_call_init (rbres->self, 0, NULL);
>
> 	return self;
Where did rbres->self come from?  Doesn't look like you initialized it. 
  You need to pass a valid Ruby object to rb_obj_call_init(), perhaps 
you intended:
<code>
	return rb_obj_call_init(self, 0, 0); /* returns self */
</code>
> }
>
> 'parent' is the Ruby object that the object marks in c_mark
>
> This is the "notifier" method of the Result object and the callback 
> used
> to call the given block:
>
> static void on_signal (xmmsc_result_t *res2, void *data)
> {
> 	/* call the block and create a new Result object from res2, too */
> 	rb_funcall ((VALUE) data, rb_intern ("call"), 1,
> 	            TO_XMMS_CLIENT_RESULT (Qnil, res2));
> }
>
> static VALUE c_notifier_set (VALUE self)
> {
> 	GET_OBJ (self, RbResult, res);
>
> 	if (!rb_block_given_p ())
> 		return Qnil;
>
> 	res->callback = rb_block_proc ();
> 	xmmsc_result_notifier_set (res->real, on_signal, (void *) 
> res->callback);
This could be your problem. We encountered a similar problem last night 
with the Rendezvous Ruby wrappers.
rb_block_proc() creates a ruby object.
your registering on_signal as your event handler, and it looks like 
what ever library you are using (you should supply more code here) will 
the pass the void* to the call back for you.  You need to show c_mark() 
so it is clear that your marking everything.
-Charlie
>
> 	return Qnil;
> }
>
> It's pretty straight-forward and the comment should explain it all :)
>
> Thanks for any hints.
>
> -- 
> Regards,
> Tilman
>