From: Tilman Sauerbeck <tilman@...>
Date: 2004-07-30T23:06:11+09:00
Subject: Re: C ext: GC claiming objects early

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;

	rb_obj_call_init (rbres->self, 0, NULL);

	return self;
}

'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);

	return Qnil;
}

It's pretty straight-forward and the comment should explain it all :)

Thanks for any hints.

-- 
Regards,
Tilman