future question

[Jacob Jozef]

Hi

 

The following runs 100% of my CPU, but when I uncomment the when-clause nothing happens (0% CPU)

(processor-count) yields 8 on my PC.

 

#lang racket

 

(define sema (make-semaphore 1))

 

(define (make-th i)

(λ ()

  (let loop ((a 0))

#;(when (zero? (modulo a #e1e6))

    (semaphore-wait sema)

    "do what you have to do without disturbing other futures"

    (semaphore-post sema))

   (loop (add1 a)))))

 

(for ((i (in-range (processor-count)))) (future (make-th i)))

 

(sleep 10)

(exit)

 

Can’t I use semaphores in futures? Help please.

I have used semaphores earlier without trouble.

Jos (Jacob J. A. Koot)

 

PS My version:

Welcome to DrRacket, version 8.2 [cs].

Language: racket [custom]; memory limit: 6000 MB.

 

[Dominik Pantůček]

Hi,

you are looking for make-fsempahore[1] and related:

===
#lang racket

(define sema (make-fsemaphore 1))

(define (make-th i)

(λ ()
(let loop ((a 0))

(when (zero? (modulo a #e1e6))

(fsemaphore-wait sema)

"do what you have to do without disturbing other futures"

(fsemaphore-post sema))

(loop (add1 a)))))
(for ((i (in-range (processor-count)))) (future (make-th i)))
(sleep 10)
(exit)

===

The above updated source spins all your cores just fine.


Cheers,
Dominik
[1]
https://docs.racket-lang.org/reference/futures.html#%28part._.Future_.Semaphores%29

[Jacob Jozef]

Hi Dominic

Thanks very much for your prompt reply.

Your response works very well.

I didn’t know there is a distinction between semaphores and fsemaphores.

You have helped me a lot.

Thanks again, Jos

--

You received this message because you are subscribed to the Google Groups "Racket Users" group.

To unsubscribe from this group and stop receiving emails from it, send an email to racket-users...@googlegroups.com.

To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/cc8c5754-9354-6367-7c62-b8c12cb60cd4%40trustica.cz.