fix: tor: Call event_base_loopbreak from the event’s callback #16405

1. 
   promag commented at 2:33 pm on July 17, 2019: member

   Calling event_base_loopbreak before event_base_dispatch has no effect. Fix this by calling event_base_loopbreak from the event’s callback. From the documentation:

   event_base_loop() will abort the loop after the next event is completed; event_base_loopbreak() is typically invoked from this event’s callback. This behavior is analogous to the “break;” statement.

   This can be tested by running the following with and without this change:

   0bitcoind -- -regtest -proxy=127.0.0.1:9050 -listen=1 -bind=127.0.0.1 -whitebind=127.0.0.1:0
   

   Fixes #16376.

2. fix: tor: Call event_base_loopbreak from the event's callback a981e749e6
3. 
   promag commented at 2:36 pm on July 17, 2019: member

   To backport.
4. 
   laanwj commented at 2:59 pm on July 17, 2019: member

   Yes, this seems the most straightforward solution. code review ACK a981e749e6553487cd48eda28e590f769e81c85c
5. promag referenced this in commit b2711b98bd on Jul 17, 2019
6. DrahtBot added the label P2P on Jul 17, 2019
7. fanquake approved
8. 
   fanquake commented at 2:48 am on July 18, 2019: member

   ACK a981e749e6553487cd48eda28e590f769e81c85c

   Tested that the change fixes the hanging behavior at shutdown using the above command.

   In regards to the code. If I understand correctly we are calling event_base_once to trigger a one-time event, and by passing EV_TIMEOUT as events, and nullptr to timeout, this causes the callback to be executed immediately. The callback calls event_base_loopbreak and that will:

   Abort the active event_base_loop() immediately."

   This is required because we haven’t yet called event_base_dispatch, which would be done just after this code.

9. 
   promag commented at 7:56 am on July 18, 2019: member

   to be executed immediately

   to be queued and called asap by the event base.

10. laanwj merged this on Jul 18, 2019
11. laanwj closed this on Jul 18, 2019

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promag laanwj fanquake

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