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

[malc <av1474@comtv.ru>]

On Fri, 2 Sep 2011, David Allsopp wrote:

> malc wrote:
> > On Fri, 2 Sep 2011, David Allsopp wrote:
> > 
> > > malc wrote:
> > > > On Fri, 2 Sep 2011, Daniel B?nzli 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...)
> > 
> > Uhm, no, it uses native API which was never publically documented to
> > begin with, and the reason for that that it provides other information
> > which is unavailable via other means.
> 
> It is documented and it is deprecated for this usage (see 
> http://msdn.microsoft.com/en-us/library/ms725506(v=VS.85).aspx) making 
> it a poor example for the specific question of querying logical 
> processor count.

Well, okay, not however that the substitute for
SYSTEM_PROCESSOR_PERFORMANCE_INFORMATION is only available starting with 
XP SP1, in any case the times provided by the kernel are wrong anyway.

All that said, Get[Native]SystemInfo (possibly with 
GetLogicalProcessorInfomration[Ex]) is better in this particular case.

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