How about using channels:
#lang racket
(define handle-channel (make-channel))
(define (handle-producer ch)
(let loop ((counter 1))
(channel-put ch counter)
(loop (add1 counter))))
(thread (lambda () (handle-producer handle-channel)))
(define (new-handle)
(channel-get handle-channel))
Alex.
On Thursday, September 1, 2016 at 5:44:30 PM UTC+8, erich 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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