Re: [Caml-list] Are refs volatile?

[Gerd Stolpmann <info@gerd-stolpmann.de>]

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Am Mittwoch, den 04.11.2015, 12:43 +0000 schrieb Richard W.M. Jones:
> Some code I wrote recently does:
> 
>   let quit = ref false in
>   let set_quit _ = quit := true in
>   Sys.set_signal Sys.sigint (Sys.Signal_handle set_quit);
>   Sys.set_signal Sys.sigquit (Sys.Signal_handle set_quit);
> 
> and later on (where `tasks' is a list of long-running tasks):
> 
>   List.iter (
>     fun task ->
>       if not !quit then task ();
>   ) tasks;
> 
> This works fine.  My question is, could a change to the compiler in
> future cause the reference to !quit to be optimized away?  And if so,
> is there a way to mark it as "volatile" (in the C sense)?

Interesting question. My guess is that it is much harder to optimize
side-effects in the presence of closures, and that it is fairly unlikely
that anybody attempts this. In this piece of code, you must be sure that
[task] doesn't set [quit], but this ref can be well hidden, and the
analysis needed to figure this out seems to be complicated.

Gerd
-- 
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Gerd Stolpmann, Darmstadt, Germany    gerd@gerd-stolpmann.de
My OCaml site:          http://www.camlcity.org
Contact details:        http://www.camlcity.org/contact.html
Company homepage:       http://www.gerd-stolpmann.de
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