MCE has gone through several revisions since the time the OP tested this. I tested without IO::Pty on my box. Amazingly, running (yum install perl-Net-OpenSSH) installed the package without checking the perl-IO-Tty dependency.

Workers in older MCE revisions closed STDOUT/STDERR prior to exiting. That was fix some time back.

$ ./mce_openssh.pl
child(1): doing ssh
unable to load Perl module IO::Pty: Can't locate IO/Pty.pm in @INC (@I
+NC contains: /media/psf/shm/trunk/examples/../lib /usr/local/lib64/pe
+rl5 /usr/local/share/perl5 /usr/lib64/perl5/vendor_perl /usr/share/pe
+rl5/vendor_perl /usr/lib64/perl5 /usr/share/perl5 .) at (eval 10) lin
+e 1, <__ANONIO__> line 2.
 at /usr/share/perl5/vendor_perl/Net/OpenSSH.pm line 756.
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Btw, the script works after installing IO::Tty (yum install perl-IO-Pty).

my $sshuser = 'remote_userid';
my $sshpwd  = 'remote_passwd';
my $device  = 'remote_device';

use MCE::Flow max_workers => 1;
use Net::OpenSSH;

mce_flow sub {
   my $wid = MCE->wid;

   MCE->sendto('stdout', "child($wid): doing ssh\n");

   my $ssh = Net::OpenSSH->new(
      $device,
      user => $sshuser,
      passwd => $sshpwd,
      master_opts => [-o => "StrictHostKeyChecking=no"],
      master_stderr_discard => 1
   );

   MCE->sendto('stdout', "child($wid): did ssh - not shown!!! \n");

};
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In summary, STDERR output is no longer lost with current MCE releases.

taken from OpenSSH.pm




sub _load_module {
    my ($module, $version) = @_;
    $loaded_module{$module} ||= do {
        do {
            local ($@, $SIG{__DIE__});
            eval "require $module; 1"
        } or croak "unable to load Perl module $module";
        1
    };
    if (defined $version) {
        local ($@, $SIG{__DIE__});
        my $mv = eval "\$${module}::VERSION" || 0;
        (my $mv1 = $mv) =~ s/_\d*$//;
        croak "$module version $version required, $mv is available"
            if $mv1 < $version;
    }
    1
}
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somewhere in here it breaks... if pm not preloaded and in MCE context.

oops, there is a bug in that part of the code that causes it to fail silently (instead of failing with an error that tells you what has gone wrong).

Try replacing it by the following version:

sub _load_module {
    my ($module, $version) = @_;
    $loaded_module{$module} ||= do {
        do {
            local ($@, $SIG{__DIE__});
            eval "require $module; 1"
        } or croak "unable to load Perl module $module";
        1
    };
    if (defined $version) {
        my $mv = do {
            local ($@, $SIG{__DIE__});
            eval "\$${module}::VERSION" || 0;
        };
        (my $mv1 = $mv) =~ s/_\d*$//;
        croak "$module version $version required, $mv is available"
            if $mv1 < $version;
    }
    1
}
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