[tor-bugs] #3199 [Tor]: Refactor periodic events

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#3199: Refactor periodic events
-------------------------------------------------+-------------------------
 Reporter:  nickm                                |          Owner:
     Type:  defect                               |         Status:
 Priority:  Very Low                             |  needs_review
Component:  Tor                                  |      Milestone:  Tor:
 Severity:  Normal                               |  0.2.8.x-final
 Keywords:  easy, tor-relay,                     |        Version:  Tor:
  027-triaged-1-deferrable, 028-triaged,         |  0.2.7
  pre028-patch                                   |     Resolution:
Parent ID:                                       |  Actual Points:
  Sponsor:  SponsorS                             |         Points:  medium
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Comment (by special):

 It makes me a little sad that events like rotate_onion_key, check_ed_keys,
 record_bridge_stats will be called once per second on clients to handle
 the unlikely case where the configuration changes and they're now
 relevant. That is consistent with previous behavior, though. They have a
 little more overhead than they used to - at least one time() and
 event_add() each.

 It wasn't obvious what returning -1 from the callback would do, but it is
 documented. A constant would help, maybe. Speaking of which:

 {{{
 +* interval time. If the returned value is larger than <b>now</b> then
 it
 +* is assumed to be a future time to poll again. */
 }}}
 From periodic.h:11. This comment is wrong; it will assert if a timestamp
 is returned.

 In periodic_event_dispatch, the log_info is done after the callback. I
 think it would make more sense before.

 I did not notice anything that moved and might be sensitive to being
 called in a different order, but I could imagine that being very subtle.

 Nitpickery:

 main.c:1612 - not new, but this function is run_connection_housekeeping,
 not connection_run_housekeeping.

 main.c:1579 - extra space before GREEDY_DESCRIPTOR_RETRY_INTERVAL

 main.c:1458 - the 3a comment is over-indented

 periodic.c:15 - greate -> greater, ground -> grounds

 LGTM otherwise.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/3199#comment:22>
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