def fork_it(&blk)
        pid = Kernel.fork do
          self.class.is_child = true
          $0 = "[ThreadsOnFork worker] parent: #{Process.ppid}"
          blk.call
        end
        self.class.child_pids << pid
        pid
      end
Forks the specified block and adds the process to the child process pool
FIXME: If blk.call breaks then the pid isn't added to child_pids and is
never shutdown