sub upto { my $stop = $_[0]; my $start = 0; for ($start..$stop) { yield $_ }; }; for my $item (upto(5)) { print "At $item\n"; }; __END__ At 1 At 2 At 3 At 4 At 5 #### sub frobnicate { print "Frobnicating\n"; }; sub frobnitz { print "Frobnitzing\n"; }; sub gargle { local *frobnicate = \&frobnitz; frobnicate(); }; my $thr1 = async { gargle() }; my $thr2 = async { gargle() }; my $thr3 = async { gargle() }; #### open my $fh, "<:async", $filename or die "Couldn't open '$filename': $!"; my $line = <$fh>; # ... do some busy work without touching $line ... print $line;