[DGD] Continuations

[nikoroleva]

Felix A. Croes <felix at dworkin.nl> wrote:
>
> nikoroleva <natasha.i.koroleva at gmail.com> wrote:
>
> > I finally took a moment to experiment with this queue. Very cool feature!
>
> A few more remarks about the queue.
>
> The point of queue->dequeueCont() should be clear: it only runs when
> there is an element to retrieve from the queue.  But you may wonder what
> the purpose of queue->enqueueCont() is.  Why not call queue->enqueue(elem)
> directly?
>
> The answer is that the queue is optimized for Hydra's concurrency.
> Suppose that there are many LPC tasks which want to use this queue.  If
> all of them called queue->enqueue(elem), then each task would modify the
> queue object, and only one of those concurrently running tasks could
> complete successfully.
>
> The queue instead offers enqueueCont(elem) to create a continuation to
> enqueue the object.  Creating that continuation does not modify the
> queue, and can be done concurrently by an unlimited number of tasks.
> The actual enqueue tasks are run from the queue object, and are serialized
> so that they do not block eachother.  They are also guaranteed to succeed,
> because they don't affect any other object.
>
> The queue could perhaps be further improved in the following manner:
>
>     Continuation enqueueCont()
>     {
>         return new ChainedContinuation("enqueue");
>     }
>
> Then you could also do:
>
>     c = new Continuation("produceElement") >> queue->enqueueCont();
>     c->runNext();
>
These remarks call to mind some of the posts about continuations from
last autumn, and build on and reinforce those posts. Some things click
now that didn't before.