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Postloop callbacks 2 #41

Merged
merged 7 commits into from Apr 13, 2018
Merged

Postloop callbacks 2 #41

merged 7 commits into from Apr 13, 2018

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@nmathewson @dgoulet-tor @tor-bot
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@nmathewson nmathewson commented Apr 5, 2018

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nmathewson added 6 commits Apr 13, 2018
@nmathewson
Disable load_geoip_file() tests on windows
ad57b12 
See bug #25787 for discussion; we should have a better fix here.
@nmathewson
Generic mechaism for "post-loop" callbacks
c5a3e2c 
We've been labeling some events as happening "outside the event
loop", to avoid Libevent starvation.  This patch provides a cleaner
mechanism to avoid that starvation.

For background, the problem here is that Libevent only scans for new
events once it has run all its active callbacks.  So if the
callbacks keep activating new callbacks, they could potentially
starve Libevent indefinitely and keep it from ever checking for
timed, socket, or signal events.

To solve this, we add the ability to label some events as
"post-loop".  The rule for a "post-loop" event is that any events
_it_ activates can only be run after libevent has re-scanned for new
events at least once.
@nmathewson
Move the "activate linked connections" logic to a postloop event.
5719dfb 
A linked connection_t is one that gets its I/O, not from the
network, but from another connection_t.  When such a connection has
something to write, we want the corresponding connection to run its
read callback ... but not immediately, to avoid infinite recursion
and/or event loop starvation.

Previously we handled this case by activating the read events
outside the event loop.  Now we use the "postloop event" logic.
This lets us simplify do_main_loop_once() a little.
@nmathewson
Move connection_ap_attach_pending(0) into a postloop event
320bd2b 
This is a second motivating case for our postloop event logic.
@nmathewson
Add a unit test for post-loop events
62f4d5a 
This test works by having two post-loop events activate one another
in a tight loop.  If the "post-loop" mechanism didn't work, this
would be enough to starve all other events.
@nmathewson
Changes files for post-loop events (25374)
2fe499e
@nmathewson nmathewson force-pushed the postloop_callbacks_2 branch from 117de42 to 2fe499e Apr 13, 2018
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@dgoulet-tor dgoulet-tor commented Apr 13, 2018

So this all lgtm! The only thing I think can be done as an extra commit is to remove the tell_event_loop_to_run_external_code() code since it is not used anymore.

@nmathewson
Remove tell_event_loop_to_run_external_code() per review
4c03af4 
(This function is no longer used.)
@tor-bot tor-bot merged commit 4c03af4 into torproject:master Apr 13, 2018
1 check was pending
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