l...@gnu.org (Ludovic Courtès) writes:
> As was reported recently by Mark and others, ‘par-map’ would only use
> ncores - 1, because the main thread was stuck in a
> ‘wait-condition-variable’ while touching one of the futures.
>
> The obvious fix is to write ‘par-map’ like this (as can be seen from
> Chapter 2 of Marc Feeley’s PhD thesis):
>
> (define (par-mapper mapper cons)
> (lambda (proc . lists)
> (let loop ((lists lists))
> (match lists
> (((heads tails ...) ...)
> (let ((tail (future (loop tails)))
> (head (apply proc heads)))
> (cons head (touch tail))))
> (_
> '())))))
Am I correct in believing that the above code would use the main thread
only for applying 'proc' to the first element of each list?
In other words, if you have 4 cores and call 'par-map' on a list of 1000
elements, the main thread will only be used to process 1 out of 1000
elements, and only 3 cores will be used to process the other 999.
Is that right?
Mark
