What are common pitfalls or gotchas with select and non-blocking I/O?

# Example of using select in non-blocking I/O in Perl
use IO::Socket;
use IO::Select;

my $socket = IO::Socket::INET->new(
    Proto    => 'tcp',
    LocalPort => 5000,
    Listen   => SOMAXCONN,
    Reuse    => 1
) or die "Could not create socket: $!";

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

while (1) {
    my @ready = $select->can_read(0);
    foreach my $fh (@ready) {
        if ($fh == $socket) {
            my $new_client = $socket->accept();
            $select->add($new_client);
            $clients{$new_client} = 1;
        } else {
            my $data = '';
            my $bytes_read = sysread($fh, $data, 1024);
            if (!defined $bytes_read) {
                warn "Error reading from client: $!";
                $select->remove($fh);
                delete $clients{$fh};
                close($fh);
            } elsif ($bytes_read == 0) {
                $select->remove($fh);
                delete $clients{$fh};
                close($fh);
            } else {
                # Handle incoming data
                print "Received data: $data";
            }
        }
    }
}