[racket] values primitive blocks future execution

I think the problem (in addition to the ones I mentioned in my previous
message) is the use of let*, etc. inside your future thunk.  These were
expanding to define-values, which seemed to be the source of the `values'
barricading.  If you rewrite `render-scene-dummy' like so:

(define (render-scene-dummy object-list)
  (let* ([f (future
             (lambda ()
               (define x (/ screen-width 2))
               (define y screen-height)
               (define ray-res (ray-cast x y sph-vec))
               (define pix-col (point-col (int-res-p ray-res)))
               #t))])
    (for* ([x (in-range (/ screen-width 2) screen-width)]
   [y screen-height])
      (let* ([ray-res (ray-cast x y sph-vec)]
     [pix-col (point-col (int-res-p ray-res))])
#t))
    (touch f))
)

I don't see any blocks on my machine.  Are you still in experimentation
mode with futures?  It seems there won't be much parallelism in this
program because you are only creating the one future.

In general, it's better to restrict the use of futures to the hottest parts
of your program; variables that will be uniform across all parallel tasks
should be defined outside the thunk.


Date: Fri, 22 Feb 2013 00:03:28 +0300
> From: Dmitry Cherkassov <dcherkassov at gmail.com>
> To: users at racket-lang.org
> Subject: [racket] values primitive blocks future execution
> Message-ID:
>         <CAN0j1dRCGY7A2WxXBYXP=
> JbLntw_-L3O7eoYJvD1VTAb+qDLYQ at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Hi list.
> I've been doing a simple ray tracer[1] and decided to parallelize it using
> futures.
>
> I've tried to use flonums everywhere and added (in-range) to loops [3]
> (over x and y coordinates).
>
> The problem is that execution of future is blocked seriously.
> (apparently by the value primitive) [2]
>
> Are there any ideas why it doesn't work?
>
> I use racket v5.3.3.
>
> [1] Complete source code: http://pastebin.com/EGSzR1Tv
>
> [2] Future visualizer screenshot: http://ompldr.org/vaGpiaQ
>     Invoked via
>     (require future-visualizer)
>     (visualize-futures (run-no-render))
>
> [3] Source code for main loop:
> (define (render-scene-dummy object-list)
>   (let* ([f (future
>            (lambda ()
>              (for* ([x (in-range (/ screen-width 2))]
>                     [y (in-range screen-height)])
>                (let* ([ray-res (ray-cast x y object-list)]
>                       [pix-col (point-col (int-res-p ray-res))])
>                  #t))
>              ))])
>
>     (for* ([x (in-range (/ screen-width 2) screen-width)]
>            [y (in-range screen-height)])
>       (let* ([ray-res (ray-cast x y object-list)]
>              [pix-col (point-col (int-res-p ray-res))])
>         #t))
>     (touch f)))
>
>
>
> --
> With best regards,
> Dmitry
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