[Caml-list] Sys.signal / Sys.set_signal broken in native code?

[Caml-list] Sys.signal / Sys.set_signal broken in native code?

[Dmitri Boulytchev]

     Hello,


     Sys.signal / Sys.set_signal doest not work in native code. The 
following code


     let _ =
       Sys.set_signal Sys.sigalrm (Sys.Signal_handle (fun _ -> failwith 
"Timeout..."));
       ignore (Unix.alarm 5);
       while true do () done


     loops forever being compiled with ocamlopt (and raises the expected 
exception with ocamlc). Am I missing something?

     Ubuntu 16.04 64bit, tried with 4.06.0 and 4.06.1


     Best regards,

     Dmitry Boulytchev,

     St Petersburg State University.

Re: [Caml-list] Sys.signal / Sys.set_signal broken in native code?

[ygrek]

On Sun, 22 Apr 2018 16:16:59 +0300
Dmitri Boulytchev <dboulytchev@gmail.com> wrote:


>      let _ =
>        Sys.set_signal Sys.sigalrm (Sys.Signal_handle (fun _ -> failwith 
> "Timeout..."));
>        ignore (Unix.alarm 5);
>        while true do () done
> 
> 
>      loops forever being compiled with ocamlopt (and raises the expected 
> exception with ocamlc). Am I missing something?

OCaml runtime turns signals into quasi-asynchronous - they are invoked only at allocation points in native code.
There is no allocation point inside empty loop so there is no chance to call signal handler.
My understanding is that having truly asynchronous signals would be a nightmare wrt runtime state
in signal handler (cf. C signal code restrictions) 

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