Very simple Multithreading with Continuation-passing style

{
 my @cc = ();

 sub cc(&) {
  my ($sub) = @_;
  push @cc, $sub;
 }

 sub cc_run() {
  while (my $sub = shift @cc) {
   $sub->();
   sleep 1;
  }
 }
}


sub first {
 my ($thread) = @_;
 print "$thread: 1 first\n";
 cc { third($thread) };
}

sub second {
 my ($thread) = @_;
 print "$thread: 2 second\n";
 cc { fourth($thread) };
}

sub third {
 my ($thread) = @_;
 print "$thread: 3 third\n";
 cc { first($thread) };
}

sub fourth {
 my ($thread) = @_;
 print "$thread: 4 fourth\n\n";
 cc { second($thread) };
}


cc { first("+") };
cc { second("*") };
cc_run;