On 2023-06-19 16:20, Andrew Tropin wrote:

> * module/ice-9/atomic.scm (atomic-box-update!): New variable.
> ---
> I was implementing some concurrent code and started to use (ice-9
> atomic), when found out that there is no procedure for updating the
> value of the atom using another function.
>
> IMHO, atomic-box-update! fits well FP paradigm (which is widely used
> across guile-based projects) in general and this module in particular
> and should be provided out of the box.  Made a draft implementation.
> LMKWYT.
>
>  module/ice-9/atomic.scm | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/module/ice-9/atomic.scm b/module/ice-9/atomic.scm
> index 2a8af901d..6bfa2e8ee 100644
> --- a/module/ice-9/atomic.scm
> +++ b/module/ice-9/atomic.scm
> @@ -25,7 +25,8 @@
>              atomic-box-ref
>              atomic-box-set!
>              atomic-box-swap!
> -            atomic-box-compare-and-swap!))
> +            atomic-box-compare-and-swap!
> +            atomic-box-update!))
>  
>  (eval-when (expand load eval)
>    (load-extension (string-append "libguile-" (effective-version))
> @@ -36,3 +37,14 @@
>    (add-interesting-primitive! 'atomic-box-set!)
>    (add-interesting-primitive! 'atomic-box-swap!)
>    (add-interesting-primitive! 'atomic-box-compare-and-swap!))
> +
> +(define (atomic-box-update! box proc . proc-args)
> +  "Atomically updates value of BOX to (APPLY PROC BOX-VALUE PROC-ARGS),
> +returns new value.  PROC may be called multiple times, and thus PROC
> +should be free of side effects."
> +  (let loop ()
> +    (let* ((old-value (atomic-box-ref box))
> +           (new-value (apply proc old-value proc-args)))
> +      (if (eq? old-value (atomic-box-compare-and-swap! box old-value new-value))
> +          new-value
> +          (loop)))))

Found one more example of the usage of this pattern in fibers
library.  Those lines by Christine Lemmer-Webber:
https://github.com/wingo/fibers/blob/581319ff13b97f2bb51dff713524aad696c5d52b/fibers/counter.scm#L37

-- 
Best regards,
Andrew Tropin