While I have stayed away from threads in Perl, usually, you need to wait for your threads to finish before you exit with your main thread. Maybe detaching the threads also keeps the main program alive. I'd try the following for kickstarting the threads:

my @threads;
my @ips = qw( 192.168.1.50 192.168.1.1 );
for my $ip (@ips) {
    push @threads, threads->new(\&polldevice,$ip, "public");
};

# Now, wait for all threads to finish:
for my $thread (@threads) {
    print "Waiting for thread $thread to finish.\n";
    my @results = $thread->join();
    print "(got @results)\n";
};
print "All threads finished.\n";
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