foreach( threads->list() ) { $_->join(); }

##</code><code>##

use threads::shared; ## at the top
...
my $running : shared = 0; ## before the main loop

...

sleep 1 while $running; ## after the main loop in-place of the join loop

sub deleteDevice($) {
    ++$running;
    .... # as now
    --$running;
}