I have a small app that queries a large (~3000) list of UDP servers, and parses thier results to be displayed in a tk window. On my local machine (Linux) it works just fine. Several other people who have tried it, however, cannot seem to get it to work. That is, it sends out the packets, but receives and parses only a few replys. I can't seem to figure it out. The general idea of what I am doing... 
sub CheckServers {
    
    # go down the list of servers
    # and sent a packet to each
    # one to request info
    
    my $socket = IO::Socket::INET->new( Proto => 'udp', 
                                        Type => SOCK_DGRAM);

    my $select = IO::Select->new($socket);
    my %responses;
        
CHECK_SERVERS:

    while (@servers){
        my $toread = $select;
        my $towrite = @servers ? $select : undef;
        my ($readref, $writeref) = 
            IO::Select->select( $toread,$towrite,undef,$timeout );
     
        last unless ($readref || $writeref);   
                
        foreach my $sock ( @{ $writeref } ) {
            
            $sent++;
            my $server = shift @servers; 
            my ($ip, $port) = split (/.:/, $server);
            
            next unless $port && $ip;

            my $paddr = sockaddr_in($port, inet_aton($ip));
                
            my $ret = $sock->send($HOST_QUERY, 0, $paddr) 
               || die "send: $!";
            $waiting{$ip} = Time::HiRes::time;
        
        }
        
        foreach my $sock ( @{ $readref } ) {    
                
            $rcvd++;
            my $rc = $sock->recv($reply, 10_000);
            next unless $rc;
            my ($port, $addr) = sockaddr_in($rc); 
            my $ip = inet_ntoa($addr); 
            
            if ( $reply ) {
                ... do stuff ...
                     }                
        
        next CHECK_SERVERS;

        }
    }
}

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In reply to Problems with select() on socket by Anonymous Monk

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