my $j = 0;
if ((my $pid = fork()) == 0) {
 # this runs in child process
 do {sleep 0.5; spin($j)} while 1;
 # normally we should put some kind of exit statement here, but the loop above is infinite
} elsif ($pid > 0) {
 # parent/main process
 ...;
 # put your loop here
 kill 1, $pid; # stop the spinner process
 waitpid $pid, 0; # this should help against zombies
} else {
 # fork returned undef
 die "fork: $!\n";
}