[racket-dev] FrTime propagation bug

Hi Marijn,

The value-now/sync procedure waits for propagation to complete before
reading a signal's value.  Would something like the following suit your
purposes?

(define a (event-receiver))
(define b (event-receiver))
(define a+b (+ (hold a) (hold b)))
(send-event a 3)
(send-event b 5)
(value-now/sync a+b)  ; read a+b after propagation => 8

Or, even simpler:

(define c (new-cell))
(define d (new-cell))
(define c+d (+ c d))
(set-cell! c 3)
(set-cell! d 5)
(value-now/sync c+d)

Greg

On Thu, Jan 12, 2012 at 12:49 AM, Marijn <hkBst at gentoo.org> wrote:

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> On 11-01-12 21:26, Gregory Cooper wrote:
> > Hi Marijn,
> >
> > FrTime propagates changes asynchronously.  When send-event returns,
> > there's no guarantee that the event has finished propagating
> > through the system. And in general, (value-now b) is not
> > well-defined, since asynchronous processing makes it difficult to
> > define what "now" means; programs should only call this if they can
> > tolerate stale values.
>
> Hi Gregory, so just to make sure I understand the implications of
> this: there is no way to do something like the following:
>
>
> #lang racket
>
> (require frtime)
>
> (define a (event-receiver))
> (define b (event-receiver))
>
> (define a+b (... ??? (merge-e a b)))
>
> (send-event a 3)
> (send-event b 5)
>
> (... ??? make sure everything is consistent again)
>
> (... ??? get the value 8 out of a+b)
>
>
> Marijn
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