workshop.p6

my $checkpoint = Supplier.new;

my $total-workers = 5;
my $units-to-build = 3;

await (1..$total-workers).map: {
  start {
    my $id = $_;

    my %who's-ready;

    my $go = Channel.new;

    $checkpoint.Supply.tap: {
      die "Oh no, something's wrong!" if %who's-ready{$_}:exists;

      %who's-ready{$_} = True;

      if %who's-ready == $total-workers {
        %who's-ready{*}:delete;
        $go.send: Any;
      }
    };

    for ^$units-to-build {
      my $duration = 3.rand;

      say "$id starts working for $duration seconds.";
      sleep $duration;
      say "$id is done, waiting.";

      $checkpoint.emit: $id;
      $go.receive;
    }
  }
}

say "All work is done!";