class Concurrent::Agent

def ns_enqueue_job(job, index = nil)
  # a non-nil index means this is an await job
  return false if index.nil? && failed?
  index ||= @queue.length
  @queue.insert(index, job)
  # if this is the only job, post to executor
  ns_post_next_job if @queue.length == 1
  true
end