[racket] future on dual processor machine

It looks like you've found a futures bug.  This is being caused by the
interaction between futures and custodians (which DrRacket is using) --
we've identified a fix, but need a little more testing to ensure that it's
working properly.  I will keep you posted here.

-James



> The program below has strange behaviour:
> I run it from DrScheme on a dual core machine with two processors.
> No other applications active.
> When I run it the first time it uses 100% of both processors.
> Running it again without leaving DrScheme, it apparently uses one processor
> at a time only, although switching frequently. CPU usage histories mirror
> each other. How come only one processor is used at a time during the second
> run?
> Leaving DrScheme, restarting DrScheme and running again gives me 100% of
> both processors again.
> In all runs processor-count returns 2.
> Thanks, Jos
>
> DrRacket, version 5.1.1.5--2011-05-09(b74c9f9/a) [3m].
> Windows 7.
> Intel Pentium dual core CPU E6500.
>
> #lang racket
> ; check that both processors are used by means of
> ; windows tool for measurement of CPU usage.
> (require racket/unsafe/ops)
> (require racket/fixnum)
> (require racket/future)
> (collect-garbage)
> (processor-count) ; -> 2
> (define N/2 #e1e8)
> (define N (* 2 N/2))
> (define V (make-fxvector N))
> (define (set-V! f r) (unsafe-fxvector-set! V f r))
>
> (define (task1)
>  (for ((i (in-range 50)))
>  (for ((k (in-range 0 N/2))) (set-V! k k))))
>
> (define (task2)
>  (for ((i (in-range 50)))
>  (for ((k (in-range N/2 N))) (set-V! k k))))
>
> ; task1 fills the first half of vector V.
> ; task2 the second half.
> ; In both tasks the ((i (in-range 50))) is inserted in order to
> ; force the program to run long enough to see its parallel effects.
>
> (define f (future task1))
> (task2)
> (touch f)
> ; Clear memory avoiding memory overflow during next run.
> (set! V #f)
> (set! f #f)
> (collect-garbage)
>
>
>
>
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