Avoid deadlocks when ensuring Olm sessions for devices #1627
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This avoids logging immediately on various code paths (including tests) where no timeout value is supplied.
This reworks tracking the Olm sessions a particular task is updating to avoid deadlocks. By ensuring we synchronously mark all sessions a task cares about as in progress from the start, we know that no other tasks will own updating a session in common, which avoids deadlocks across multiple tasks that might be working on a shared set of devices. Fixes element-hq/element-web#16194
This removes the unused `reject` path for in progress Olm sessions to simplify understanding the code.
This removes extra steps that duplicated deletion of an in progress Olm session. Resolving the promise handles removing the session from the in progress set, so there's no need to do it again. There's also no need to delete from `resolveSession`, as it's okay to resolve a promise multiple times.
dbkr
approved these changes
Mar 2, 2021
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This reworks tracking the Olm sessions a particular task is updating to avoid deadlocks. By ensuring we synchronously mark all sessions a task cares about as in progress from the start, we know that no other tasks will own updating a session in common, which avoids deadlocks across multiple tasks that might be working on a shared set of devices.
The potential for deadlocks first appeared with #857 (2 years ago), but I believe it would be unlikely for most users to trigger this deadlock during normal usage. The app would need to be sluggish enough to permit stacking up several messages in different rooms with devices in common, which is most likely only possible on larger accounts. In any case, with this change, this process should now avoid deadlocks in all cases.
Fixes element-hq/element-web#16194