class Google::Cloud::Env::LazyValue

def get *extra_args
  @mutex.synchronize do
    # Wait for any backfill to complete, and handle expiration first
    # because it might change the state.
    wait_backfill
    do_expire if should_expire?
    # Main state handling
    if @retries.finished?
      # finished state: return value or error
      return cached_value
    elsif !@compute_notify.nil?
      # computing state: wait for the computing thread to finish then
      # return its result
      wait_compute
      return cached_value
    else
      # pending state
      cur_time = Process.clock_gettime Process::CLOCK_MONOTONIC
      # waiting for the next retry: return current error
      raise @error if @expires_at && cur_time < @expires_at
      # no delay: compute in the current thread
      enter_compute cur_time
      # and continue below
    end
  end
  # Gets here if we just transitioned from pending to compute
  perform_compute extra_args
end