CODEWITHSUNDEEP
unixocamlsignalsposix
vog
vog

Reputation: 25627

How to convert OCaml signal to POSIX signal or string?

I run a subprocess from an OCaml program and check its termination status. If it exited normally (WEXITED int), I get the expected return code (0 usually indicating success).

However, if it was terminated by a signal (WSIGNALED int), I don't get the proper POSIX signal number. Instead, I get some (negative) OCaml specific signal number.

How do I convert this nonstandard signal number to a proper POSIX signal number, for proper error reports? Alternatively, how do I convert this number to a string?

(I'm aware that there are tons of named integer values like Sys.sigabrt, but do I really have to write that large match statement myself? Moreover, I don't get why they didn't use a proper variant type in the first place, given that those signal numbers are OCaml specific anyway.)

Upvotes: 1

Views: 162

Answers (1)

Jeffrey Scofield
Jeffrey Scofield

Reputation: 66813

There is a function in the OCaml runtime that does this conversion (naturally). It is not kosher to call this function, but if you don't mind writing code that can break in future releases of OCaml (and other possibly bad outcomes), here is code that works for me:

A wrapper for the OCaml runtime function:

$ cat wrap.c
#include <caml/mlvalues.h>

extern int caml_convert_signal_number(int);

value oc_sig_to_host_sig(value ocsignum)
{
    /* Convert a signal number from OCaml to host system.
     */
    return Val_int(caml_convert_signal_number(Int_val(ocsignum)));
}

A test program.

$ cat m.ml
external convert : int -> int = "oc_sig_to_host_sig"

let main () =
    Printf.printf "converted %d -> %d\n" Sys.sigint (convert Sys.sigint)

let () = main ()

Compile the program and try it out:

$ ocamlopt -o m -I $(ocamlopt -where) wrap.c m.ml
$ ./m
converted -6 -> 2

All in all, it might be better just to write some code that compares against the different signals defined in the Sys module and translates them to strings.

Upvotes: 1

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