How to test for reliable select()?

[Lightknight]

I'm writing a module, Parallel::Loops, that now uses IO::Select on a pipe's handles. However select only works on windows for sockets. And perlport says that:

       select  Only implemented on sockets. (Win32, VMS)
               Only reliable on sockets. (RISC OS)

I guess I could test for Win32 || VMS || RISC_OS somehow (by finding what $^O is on all those platforms?). But that is brittle. Is there "a better way" to judge whether select works without having to fork and without it costing (too much) runtime? ($Config{d_select} eq 'define') seems to be true for both linux and Windows, unhelpfully.

[BrowserUk]

Is there "a better way" to judge whether select works without having to fork and without it costing (too much) runtime?

This is as much a question as a suggestion.

On an OS where select does work on pipes, if you create a pipe, write to the write handle and then immediately select on the read handle with a timeout, shouldn't you get the read handle's fileno returned immediately? On Windows, you get 0:

pipe $in, $out;;

print $out 'fred';;

$si = ''; vec $si, fileno( $in ), 1;;

print select $si, undef, undef, 0.1;;
0 0.1

[ambrus]

You might also try to use a proper portable event module like EV which will do as much as it can on many platforms including Win32.

[ikegami]

Sockets can be used instead of pipes. The following works on Windows (and on unix, of course):

use Socket qw( AF_UNIX SOCK_STREAM PF_UNSPEC );

sub _pipe {
    socketpair($_[0], $_[1], AF_UNIX, SOCK_STREAM, PF_UNSPEC)
        or return undef;
    shutdown($_[0], 1);  # No more writing for reader
    shutdown($_[1], 0);  # No more reading for writer
    return 1;
}

(From Re^4: why IPC::Open3 can't execute MS-DOS "dir" command?)