Did you look at using a semaphore? That's what I would try, but I also
didn't know about box-cas!
Thanks,
Dave
On 09/01/2016 10:49 AM, Erich Rast wrote:
Wow, I didn't know about box-cas! That seems to be a good solution in
this case. Thanks!
-- Erich
On Thu, 1 Sep 2016 09:37:06 -0300
Gustavo Massaccesi <gust...@oma.org.ar> wrote:
What about box-cas! ?
https://docs.racket-lang.org/reference/boxes.html#%28def._%28%28quote._~23~25kernel%29._box-cas%21%29%29
Something like:
;---
#lang racket
(define handle-counter (box 1))
(define (new-handle)
(define old (unbox handle-counter))
(define new (add1 old))
(unless (box-cas! handle-counter old new)
(new-handle))
old) ; or new ?
;---
Gustavo
On Thu, Sep 1, 2016 at 6:44 AM, Erich Rast <er...@snafu.de> wrote:
This question is also about style. Take an admittedly ugly
counter like this
;; increasing counter for handles
(define handle-counter 1)
(define (new-handle)
(begin0
handle-counter
(set! handle-counter (add1 handle-counter))))
Various threads may call (new-handle) concurrently, so I need to
ensure that every thread gets a unique handle. However, the handles
need not reflect the temporal order of the calling sequence in any
way. It's hard to debug but I believe I've seen a case in which the
above code has assigned the same handle to concurrent threads, as
one would expect.
So basically new-handle needs to be in a critical section, right? I
feel stupid that I don't know the answer, but how do I do this?
In the docs I've found ffi/unsafe/atomic, but this seems like
overkill and is unsafe and only intended for the FFI.
Second question: Should I use a parameter or something else for this
construct, and if so, what are the benefits of doing so? What would
be the 'right' way of providing unique numbers in a synchronized
way?
Best,
Erich
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