Re: map-par slower than map

[Damien Mattei <damien.mattei@gmail.com>]

i do not see what has changed in your code ?
really strange,even with bad code the moment it crash should be the same,
sometimes works,crash or freeze....

On Thu, Oct 13, 2022 at 2:41 PM Olivier Dion <olivier.dion@polymtl.ca>
wrote:

> On Thu, 13 Oct 2022, Damien Mattei <damien.mattei@gmail.com> wrote:
> > the code did not worked when data length were more little than number of
> > cpus (6 on my host) (iota 5) returns #unsepcified:
>
> Yeah sorry I miss indended the output and the rest.  Here's a version
> that should work:
> --8<---------------cut here---------------start------------->8---
> (use-modules
>  (srfi srfi-1)
>  (ice-9 threads))
>
> (define* (par-map-vector proc input
>                          #:optional
>                          (max-thread (current-processor-count)))
>
>   (let* ((block-size (quotient (vector-length input) max-thread))
>          (rest (remainder (vector-length input) max-thread))
>          (output (make-vector (vector-length input) #f)))
>     (when (not (zero? block-size))
>       (let ((mtx (make-mutex))
>             (cnd (make-condition-variable))
>             (n 0))
>         (fold
>          (lambda (scale output)
>            (begin-thread
>             (let lp ((i 0))
>               (when (< i block-size)
>                 (let ((i (+ i (* scale block-size))))
>                   (vector-set! output i (proc (vector-ref input i))))
>                 (lp (1+ i))))
>             (with-mutex mtx
>               (set! n (1+ n))
>               (signal-condition-variable cnd)))
>            output)
>          output
>          (iota max-thread))
>         (with-mutex mtx
>           (while (not (< n max-thread))
>             (wait-condition-variable cnd mtx)))))
>     (let ((base (- (vector-length input) rest)))
>       (let lp ((i 0))
>         (when (< i rest)
>           (let ((i (+ i base)))
>             (vector-set! output i (proc (vector-ref input i))))
>           (lp (1+ i)))))
>     output))
> --8<---------------cut here---------------end--------------->8---
>
> --
> Olivier Dion
> oldiob.dev
>