RE: [Caml-list] Cross-platform cpu count

[David Allsopp <dra-news@metastack.com>]

malc wrote:
> On Fri, 2 Sep 2011, Daniel Bünzli wrote:
> 
> > Hello,
> >
> > Can anybody confirm me that the following code works on cygwin :

It won't - Sys.os_type returns "Cygwin" and getconf isn't in Cygwin either - http://cygwin.com/ml/cygwin/2010-12/msg00435.html (actually, it may be now - I haven't upgraded my Cygwin in a while - but it'll be a recent addition)

> >
> > let cpu_count () =
> >   try match Sys.os_type with
> >   | "Win32" -> int_of_string (Sys.getenv "NUMBER_OF_PROCESSORS")
> >   | _ ->
> >       let i = Unix.open_process_in "getconf _NPROCESSORS_ONLN" in
> >       let close () = ignore (Unix.close_process_in i) in
> >       try Scanf.fscanf i "%d" (fun n -> close (); n) with e -> close ();
> raise e
> >   with
> >   | Not_found | Sys_error _ | Failure _ | Scanf.Scan_failure _
> >   | End_of_file | Unix.Unix_error (_, _, _) -> 1
> >
> > Thanks,
> >
> 
> http://repo.or.cz/w/apc.git/blob/55de75ccb853f5e4443fd484e5eb95e1342e72bd:
> /ml_apc.c

The C code here uses a deprecated API call (probably for Windows NT 4 compatibility). If you do end up using a C stub, use GetSystemInfo (http://msdn.microsoft.com/en-us/library/ms724381(v=vs.85).aspx) - it's easier to call. It's used in the OCaml runtime - see byterun/win32.c. Personally, even for something where it's unimportant, I'd be nervous relying on an environment variable (which can be edited...)


David