From: Edwin Van leeuwen <edder@...>
Date: 2007-11-06T02:25:29+09:00
Subject: Pulseaudio c extension callback function

Hi all,

I started working on a ruby wrapper for pulseaudio. I am a bit out of my
depth here, because my c experience is very limited and very rusty and I
am kinda stuck. The library is basically event driven. You attach some
callback function, start the mainloop and wait for events. In c you
would basically the following:

static void
callback( pa_context *c, void *userdata )
{
}

pa_mainloop *m = pa_mainloop_new();
pa_mainloop_api *api = pa_mainloop_get_api( m );
pa_context *context = pa_context_new(api, "name");
/* Here the callback function is attached */
pa_context_set_state_callback( context, callback, userdata );
pa_context_connect( connect, NULL, 0, NULL);

The interesting part is the callback function, which is defined as
follows:

static void
callback( pa_context *c, void *userdata )
{
}

I now want to define my own callback function and have it change the
status of my context object. Then I can define listeners in ruby on the
status method and will be home free. The problem is to somehow pass the
current context object to the c based callback function. My context
class is just a wrapper around pa_context, so ideally I could use
pa_context *c to "find" my object again, but if I use Data_Wrap_Struct
it will create a new context object won't it? The closest I came was:

static void
callback( pa_context *c, void *klass )
{
  VALUE obj;
  obj = * (VALUE *) klass;
  rb_funcall( obj, rb_intern( "status=" ), 1, INT2NUM(2) );
}

static VALUE
cContext_connect( VALUE klass )
{
  pa_context_set_state_callback( DATA_PTR( klass ), callback, &klass );
  pa_context_connect(DATA_PTR( klass ), NULL, 0, NULL);
  return klass;
}

but then I got the following error:
NoMethodError: undefined method `status=' for
PulseAudio::Mainloop:0xb79ac9ac>
(I have no clue where this mainloop object comes from, except that it is
ofcourse the mainloop that will call the callback function)

Also I have the feeling this could introduce problems with the GC
cleaning up my context object, because officialy it's not referenced
anymore (but I'm reasonably clueless about memory management and
pointers etc).

Does anyone have any pointers for me :) ?

Cheers,

Edwin
-- 
Posted via http://www.ruby-forum.com/.