send queue: make SendHandle::abort()/update() more precise
#3632
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Using `SendHandle::abort()` after the event has been sent would look like a successful abort of the event, while it's not the case; this fixes this by having the state store backends return whether they've touched an entry in the database.
bnjbvr
changed the title
SendHandle::abort()/update() more precise
Codecov ReportAttention: Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## main #3632 +/- ##
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- Coverage 84.21% 84.18% -0.04%
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Files 256 256
Lines 26583 26593 +10
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Hits 22387 22387
- Misses 4196 4206 +10 ☔ View full report in Codecov by Sentry. |
There were two disconnected sources of truth for the state of event to be sent: - it can or cannot be in the in-memory `being_sent` map - it can or cannot be in the database Unfortunately, this led to subtle race conditions when it comes to editing/aborting. The following sequence of operations was possible: - try to send an event: a local echo is added to storage, but it's not marked as being sent yet - the task wakes up, finds the local echo in the storage,... - try to edit/abort the event: the event is not marked as being sent yet, so we think we can edit/abort it - ... having found the local echo, it is marked as being sent. This would result in the event misleadlingly not being aborted/edited, while it should have been. Now, there's already a lock on the `being_sent` map, so we can hold onto it while we're touching storage, making sure that there aren't two callers trying to manipulate storage *and* `being_sent` at the same time. This is pretty tricky to test properly, since this requires super precise timing control over the state store, so there's no test for this. I can confirm this avoids some weirdness I observed with `multiverse` though.
Hywan
approved these changes
Jul 1, 2024
| @@ -693,20 +708,22 @@ impl QueueStorage { | |||
| &self, | |||
| transaction_id: &TransactionId, | |||
| ) -> Result<bool, RoomSendQueueStorageError> { | |||
| // Note: since there's a single caller (the room sending task, which processes | |||
| // events to send linearly), there's no risk for race conditions here. | |||
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Using
SendHandle::abort()after the event has been sent would look like a successful abort of the event, while it's not the case; this fixes this by having the state store backends return whether they've touched an entry in the database.Found thanks to
multiverse.Part of #3361.