joule-moq-relay: a fan-out holds up no other track, and each core has its own socket #587

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dcharlot merged 1 commit from relay/fanout-shards into main 2026-11-03 00:48:02 -05:00

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2026-11-02

Transaction Science

joule-moq-relay: a fan-out holds up no other track, and each core has its own socket ...

A big room's fan-out held the relay's one lock for as long as it took to reach
every subscriber, so every other room waited. A track's subscribers are now copy
on write: a fan-out takes a snapshot under the lock and delivers outside it, so
the time under the lock no longer grows with the audience.

With a snapshot, a fan-out could still push to a subscription that has just
left, which would put a stream after its cancel or past its PUBLISH_DONE count.
So a subscription is marked gone under its own lock, and a fan-out holds that
lock across each push: a push comes before the mark, or sees it and isn't made.

One UDP socket and one endpoint driver carried every peer's packets. The
listener now binds one socket per core on its one port, each its own endpoint.
Steering by address, which SO_REUSEPORT does by default, would end a session
whenever a viewer's address changed: its packets would reach a socket holding no
such connection. So a small kernel filter steers by the first byte of the
connection ID, and each socket's endpoint issues IDs that come back to it.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

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