[racket] Futures and shared data structure

Oh, probably you can recover that by judicious use of the unsafe
primitives (unsafe-fx+ and unsafe-fx= for example). The for macro is
not doing anything you can't do yourself, fwiw. (Also, fwiw, unless
you have a simple loop body, it probably won't matter too much
anyways.)

Robby

On Mon, Dec 20, 2010 at 7:23 PM, Eduardo Bellani <ebellani at gmail.com> wrote:
> 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.
>