Re: Musings on RxAda

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Wed, 21 Oct 2015 05:12:40 -0700 (PDT), Hadrien Grasland wrote:

> Reading through my post again, I should 1/Apologize for the missing words
> here and there and 2/Point out that my implementation of Observable is
> mostly synchronous, because all the costly mapping work occurs within the
> accept rendezvous.
> 
> To make an asynchronous Observer would require quite a couple more tweaks,
> allowing the Observer task to save its entry parameters and use them once
> the computation is over. In particular, the output channel should be
> passed by access, rather than by in out value.
> 
> This does not, however, void my core point that Ada's accessibility rules
> would end up getting in our way if we wanted to implement something like
> ReactiveX for Ada.

Not going to pretend understanding what are you talking about, but
synchronous vs. asynchronous in the context of publisher / subscriber is
determined by whether the publisher is blocked by subscriber(s) or not.

From that point of view using tasks or other synchronization mechanism in
the non-blocking (and thus asynchronous, and thus marshaling) scenario is
straight out wrong. See? If you block, it is not asynchronous.

A proper design pattern for non-blocking (and thus non-delivery guaranteed)
1-n publisher / subscriber scenario is a blackboard or sets of queues on
the subscriber's side. Neither require tasks, nor access types (no in the
form that something gets allocated in a conventional memory pool).

Yes, at some point you will need to defeat the type system. That is a job
for stream attributes, "for address use", or a fake memory pool. Either
would work.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de