Re: [Vala] Questions on async functions

[Fredderic Unpenstein <magentus gmail com>]

On 3 February 2010 12:36, Nor Jaidi Tuah <norjaidi tuah ubd edu bn> wrote:
> Q1.
> What is the recommended way of aborting an
> async function so that another invocation can
> be made only after the previous one has
> stopped, thus ensuring that there is at most
> one invocation at any time?

Sounds like a queue and a trampoline would be of use.

Throw each async function into a queue, and then invoke a trampoline
function in its place which in turn invokes the first item off the
queue.  Have it check a flag, and remove the item from the queue if
set, also resetting the flag.  The async function can then set the
flag before it finishes to signal that it's done, and check the flag
each time it resumes to see if it needs to clean up and quit (the
flags already set in this case, so it needn't worry about setting it).

I haven't actually used async's, so I'm not sure of the specifics, but
I've used that structure to simulate pretty much exactly what you're
suggesting.  In my case, each "async function" had an initialiser that
built and queued a structure with all the required variables, plus one
which was plugged into a switch/case statement containing the
individual segments of code, and updated to advance onto the next one
on the next resume.  Yielding from within a loop got a little
interesting, and it was a pain to follow at times, but it worked.
Same pattern should work for you.


> Q2.
> Any hope of getting the following replaced
> with a better syntax? :-)
>   Idle.add(async_function.callback);
>   yield;
> Why not simply:
>   yield;

Does your suggested syntax cover the case above?


Fredderic