Re: [Vala] Combining async methods with external processes

[Jan Hudec <bulb ucw cz>]

On Fri, Nov 19, 2010 at 13:25:11 +0100, pancake wrote:
> you are using coroutines which are not designed to "run stuff in
> background".
>
> coroutines are designed to run collaborative code which hangs if one of the
> parts doesn't pass the token when necessary.
>
> You have to use threads, or an idle task if you have a mainloop.

Async methods are NOT coroutines(*). They ARE transformation of functions to
let them finish in response to an event in the main loop (idle or not).

Oh, and avoid threads as long as you can -- synchronization is a LOT of
trouble. And running another main loop in the other thread to get
spawn_async_with_pipes working there is even more.

> On 11/19/10 08:34, James Moschou wrote:
> > Hello,
> >
> > I want to perform a series of tasks one after the other, but in the
> > background. So I have:
> >
> > async bool perform_tasks () {
> >     bool result = yield task1 ();
> >     if (result)
> >         result = yield task2 ();
> >     if (result)
> >         result = yield task3 ();
> >
> >     Idle.add (perform_tasks.callback)

You can attach the .callback to any event source in the same way. So e.g.
when data arrive from the process or the child terminates etc.

> >     yield;
> >     return result;
> > }
> >
> > more or less.
> >
> > One of the tasks however spawns a new process, and I'm not sure how
> > the callback from this process is supposed to fit into Vala's way of
> > doing async programming, i.e. Process.spawn_async_with_pipes () isn't
> > actually an "async" method.

But it's easy to wrap it in one. Just spawn_async_with_pipes and arrange the
.callback to be called when results are available and yield.


(*) They are not coroutines, because they are not running in parallel with
the caller. The not yet implemented generator functions would be coroutines.

-- 
                                                 Jan 'Bulb' Hudec <bulb ucw cz>