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fix(sync): Avoid missed long-poll wake-ups #2068

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Aranjedeath merged 2 commits from eleboucher/continuwuity:fix/sliding-sync-reliability into main 2026-08-02 16:21:00 +00:00
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eleboucher commented 2026-07-28 12:55:14 +00:00
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Avoid missed long-poll wake-ups in /sync and simplified sliding sync.

Previously, a request collected its response before registering its wake waiter. A room update arriving in that gap could be missed, leaving the client waiting until its timeout even though new data was already available. Simplified sliding sync also returned the empty response built before the wake, requiring another client request before the update appeared.

This change subscribes to a per-user generation watch before collecting data. Wakes are retained and coalesced, so updates during collection are observed when the request reaches its wait point. Both sync endpoints re-collect once after a wake; sliding sync returns the newly collected response directly.

Sliding sync delays known-room updates and to-device acknowledgement until the response being returned is selected. A discarded first collection therefore cannot advance connection state or consume to-device events.

This is lighter than the previous database-watcher approach: each request has one per-user receiver, wake-ups coalesce, and a request performs at most two collections. There is no polling or retry loop.

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<!-- In order to help reviewers know what your pull request does at a glance, you should ensure that 1. Your PR title is a short, single sentence describing what you changed 2. You have described in more detail what you have changed, why you have changed it, what the intended effect is, and why you think this will be beneficial to the project. If you have made any potentially strange/questionable design choices, but didn't feel they'd benefit from code comments, please don't mention them here - after opening your pull request, go to "files changed", and click on the "+" symbol in the line number gutter, and attach comments to the lines that you think would benefit from some clarification. --> Avoid missed long-poll wake-ups in `/sync` and simplified sliding sync. Previously, a request collected its response before registering its wake waiter. A room update arriving in that gap could be missed, leaving the client waiting until its timeout even though new data was already available. Simplified sliding sync also returned the empty response built before the wake, requiring another client request before the update appeared. This change subscribes to a per-user generation watch before collecting data. Wakes are retained and coalesced, so updates during collection are observed when the request reaches its wait point. Both sync endpoints re-collect once after a wake; sliding sync returns the newly collected response directly. Sliding sync delays known-room updates and to-device acknowledgement until the response being returned is selected. A discarded first collection therefore cannot advance connection state or consume to-device events. This is lighter than the previous database-watcher approach: each request has one per-user receiver, wake-ups coalesce, and a request performs at most two collections. There is no polling or retry loop. <!-- Example: This pull request allows us to warp through time and space ten times faster than before by double-inverting the warp drive with hyperheated jump fluid, both making the drive faster and more efficient. This resolves the common issue where we have to wait more than 10 milliseconds to engage, use, and disengage the warp drive when travelling between galaxies. --> <!-- Closes: #... --> <!-- Fixes: #... --> <!-- Uncomment the above line(s) if your pull request fixes an issue or closes another pull request by superseding it. Replace `#...` with the issue/pr number, such as `#123`. --> **Pull request checklist:** <!-- You need to complete these before your PR can be considered. 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Aranjedeath approved these changes 2026-08-02 15:22:06 +00:00
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nex reviewed 2026-08-02 15:38:14 +00:00
src/api/client/sync/v5.rs
@ -111,0 +148,4 @@
}
}
// Typing never wakes a sync loop, so collect it after the long poll settles.
nex commented 2026-08-02 15:38:14 +00:00
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I think typing is supposed to wake sync, is it not?

I think typing is supposed to wake sync, is it not?
eleboucher commented 2026-08-02 16:09:06 +00:00
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yep you are right sorry

yep you are right sorry
👍 1
Aranjedeath marked this conversation as resolved
nex approved these changes 2026-08-02 15:55:10 +00:00
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fix(sync): Wake sync loops on typing updates
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nex approved these changes 2026-08-02 16:09:58 +00:00
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