ice-9 threads parallel

ice-9 threads parallel

[Vok Vojwo]

On my system current-processor-count returns 2. I use random with the
same seed: first in normal evaluation order and second in parallel.
But the two evaluations return the same result. I expected that the
order of the random numbers differs but it is the same. Why?

This is the example:

(use-modules (ice-9 threads))

(define (slow-random)
  (sleep 1)
  (random 10))

(begin
  (set! *random-state* (seed->random-state 42))
  (values
   (list
     (slow-random)
     (slow-random)
     (slow-random)
     (slow-random)
     (slow-random))
   (list
     (slow-random)
     (slow-random)
     (slow-random)
     (slow-random)
     (slow-random))))

(begin
  (set! *random-state* (seed->random-state 42))
  (parallel
   (list
     (slow-random)
     (slow-random)
     (slow-random)
     (slow-random)
     (slow-random))
   (list
     (slow-random)
     (slow-random)
     (slow-random)
     (slow-random)
     (slow-random))))

(current-processor-count)

Re: ice-9 threads parallel

[Andy Wingo]

On Wed 26 Oct 2011 17:38, Vok Vojwo <ceving@gmail.com> writes:

> On my system current-processor-count returns 2. I use random with the
> same seed: first in normal evaluation order and second in parallel.
> But the two evaluations return the same result. I expected that the
> order of the random numbers differs but it is the same. Why?

Works for me.  Perhaps you have some future running that is taking up
one of the CPUs already?

Andy
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