[racket] Futures and shared data structure

Thanks for all the attention Robby, and I am glad that I could help find
some improvement space.

The sad part is that for the new loop there is an increase of about 100%
in the processing time, I guess it is because of the efficiency provided
by the in-vector inside the for.

Cool list, as usual.

On 12/20/2010 07:48 PM, Robby Findler wrote:
> On Mon, Dec 20, 2010 at 1:02 PM, Eduardo Bellani <ebellani at gmail.com> wrote:
>> My output to your suggested approach is
>>
>> GC [minor] at 1514740 bytes; 818464 collected in 4 msec
>> GC [minor] at 2142928 bytes; 678980 collected in 4 msec
>> GC [minor] at 4424700 bytes; 1509104 collected in 12 msec
>> GC [minor] at 4999304 bytes; 614508 collected in 16 msec
>> GC [minor] at 8337384 bytes; 1957728 collected in 20 msec
>> GC [minor] at 10529324 bytes; 1709172 collected in 24 msec
>> GC [minor] at 14245196 bytes; 2815768 collected in 28 msec
>> GC [minor] at 19109972 bytes; 4515808 collected in 48 msec
>> GC [minor] at 20287336 bytes; 4153060 collected in 32 msec
>> GC [minor] at 416134292 bytes; -27108 collected in 1652 msec
>> cpu time: 2660 real time: 2657 gc time: 1652
>> cpu time: 1000 real time: 1001 gc time: 0
>> 2 success(es) 0 failure(s) 0 error(s) 2 test(s) run
>> 0
>>
>> Which for me is not helpful. Any more suggestions?
> 
> I get the following line of output (in the development version):
> 
>   future: 0 waiting for runtime at 1292881244093.291016: values
> 
> and, sure enough, looking at the expansion of the loop:
> 
>   (for ([i (in-vector some-data)]) i)
> 
> I see that it uses multiple values which, I believe are not safe for futures.
> 
> I believe that this is a recent change and hopefully whoever did it
> will fix it (I'll post separately about this). But in the meantime,
> the program below produces these two 'time' lines for me:
> 
>   cpu time: 1586 real time: 845 gc time: 0
>   cpu time: 1596 real time: 1595 gc time: 0
> 
> which indicates that the two loops happened in parallel in the first
> case and not in the second.
> 
> Robby
> 
> #lang racket
> 
> (require racket/future
>          rackunit
>          rackunit/text-ui
>          racket/fixnum)
> 
> (define DATA (make-vector 99999999 'datum))
> 
> (define-test-suite read-from-shared
>   (test-suite "with futures"
>               (check-equal?
>                (time (let ([f (future (λ () (read-data DATA)))])
>                        (read-data DATA)
>                        (touch f)))
>                (void)))
> 
>   (test-suite "no futures"
>               (check-equal?
>                (time (read-data DATA)
>                      (read-data DATA))
>                (void))))
> 
> (define (read-data some-data)
>   (let ([end (vector-length some-data)])
>     (let loop ([i 0])
>       (unless (fx= i end)
>         (vector-ref some-data i)
>         (loop (fx+ i 1))))))
> 
> (collect-garbage) (collect-garbage)
> (run-tests read-from-shared)


-- 
Eduardo Bellani

omnia mutantur, nihil interit.