async.py 文件源码

def seconds_until_wakeup(cls):
    """
    Calculate delay until next timer expires, or None if no timers are
    set and we should wait indefinitely.  Rounds up to avoid spinning
    in select() or poll().  We could calculate fractional seconds in
    the right units instead, but select() and poll() don't even take
    the same units (argh!), and we're not doing anything that
    hair-triggered, so rounding up is simplest.
    """
    if not timer_queue:
      return None
    now = rpki.sundial.now()
    if now >= timer_queue[0].when:
      return 0
    delay = timer_queue[0].when - now
    seconds = delay.convert_to_seconds()
    if delay.microseconds:
      seconds += 1
    return seconds