Here the event Logger is rewritten as a service with a main loop instead
of mutexes. This loop has a select with essentially two legs: incoming
events, and subscription changes. When both are possible select will
chose one randomly, thus ensuring that in practice unsubscribes will
happen timely and not block the system.
Instead of just immediately dropping the event if the subscription isn't
ready to receive it, give it 15 ms to catch up. The value 15 ms is
grabbed out of thin air - it just seems reasonable to me.
The timer juggling makes the event send pretty much exactly twice as
slow as it was before, but we're still under a microsecond. I think it's
negligible compared to whatever event that just happened that we're
interested in logging (usually a file operation of some kind).
benchmark old ns/op new ns/op delta
BenchmarkBufferedSub-8 475 950 +100.00%
benchmark old allocs new allocs delta
BenchmarkBufferedSub-8 4 4 +0.00%
benchmark old bytes new bytes delta
BenchmarkBufferedSub-8 104 117 +12.50%
GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3960
Events API consumers rely on being able to detect that events were skipped
by the fact that the event ID has increased by more than 1. This is
documented, and is absolutely necessary when trying to maintain a local
model of Syncthing's state.
With the introduction of LocalChangeDetected, which is not exposed to the
Events API, this contract was broken.
This commit introduces separate concepts of a "Global ID" and a
"Subscription ID". The Global ID of an event is unique across all
subscriptions. The Subscription ID is local to a particular subscription,
and always increments by 1. They are both exposed over the Events API, but
the Subscription ID uses the key "id" for backwards compatibility, and
the "?since=xx" parameter refers to the Subscription ID (making the Global
ID for information only).
GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3351
LGTM: calmh
Resetting the timeout doesn't fully cut it, as it may timeout after we
got an event and be delivered later. This should fix it well enough for
the moment. https://github.com/golang/go/issues/11513
