Re: [Vala] Proposal for asynchronous DBus calls.

["Christian Hergert" <christian hergert gmail com>]

For tasks, you have two options.

1) Create a GTask with a callback and user_data.
2) Inherit from GTask and implement the execute (and optionally,
cancel) methods.

Keen observers will notice my challenge right away. Yes, I inherit
from GObject for reference counting and general ease of use.  It was a
tough choice.  That may make scalability an interesting feat without
reusing tasks with a sort of free-list (a la threading building
blocks).

Point being, your shared variables will live in the "target" of your GTaskFunc.

And the prototype for sake of link jumping.

typedef GTask* (*GTaskFunc) (GTask *task, GError **error, gpointer user_data);

Notice how a task/callback/errback can pause further execution of the
state machine by returning another task immediately.  Errback's will
have the option to free and unset error to allow for further
processing of the callback chain.  Not quite sure how to handle this
in vala bindings yet. I'm considering dropping error from the
prototype and adding it as tasks methods (task.{get/set}_error).

-- Christian

On Fri, Oct 17, 2008 at 1:05 AM, Sam Liddicott <sam liddicott com> wrote:
> * Christian Hergert wrote, On 17/10/08 08:06:
> > This isn't totally applicable, but I thought I'd mention it before too
> > much more async voodo.
> >
> > I've been working on an asynchronous toolkit library for GObject so
> > that once we get "yield return/yield break" support I can implement my
> > ideas I posted earlier.
> >
> > The library is called GTask and can be found on github[1].  For a
> > quick, totally out of context example:
> >
> > var task = new Task (_ => {
> >     debug ("im in worker thread");
> > });
> >
> > task.add_callback (_ => {
> >     debug ("im in main thread, by default");
> > });
> >
> > task.add_errback (_ => {
> >     debug ("i can resolve an asynchronous error");
> > });
> >
> > You can build complex callback/errback chains just like in Python
> > Twisted.  By default, the task scheduler will dispatch callbacks and
> > errbacks from the main thread to ease locking hell for GUI
> This looks a similar pattern to that used in samba's composite connect;
> I think it is useful.
>
> How will shared variables be expressed?
>
> Sam