Four perf wins from the round-4 audit, all in the steady-state hot path
(audio rooms run at ~50 datagrams/sec/participant).
Perf #1 — ACK frame gating (saves a frame + bandwidth on every drain):
AckTracker.buildAckFrame now returns null when no new ack-eliciting
packet has arrived since the last build. Pre-fix the writer emitted a
redundant ACK frame on every outbound packet (~50/sec each direction)
even when the only inbound traffic since last drain was ACK-only.
RFC 9000 §13.2 only requires ACKs in response to ack-eliciting
packets within max_ack_delay; gating on ackElicitingPending satisfies
that without delay-timer machinery.
Perf #11 — AckTracker.purgeBelow short-circuit:
Common case: peer ACKs a high PN, we already pruned below it. Pre-fix
triggered a full ListIterator walk anyway. Now bails out when the
tail's start is already above the threshold.
Perf #9 — Flow-control dirty-set:
QuicStream gains a receiveDirtyForFlowControl flag set by the parser
when readContiguous advances the frontier. The writer's
appendFlowControlUpdates now skips per-direction-window lookup +
threshold comparison for streams whose flag is unset. Big win for
multi-stream sessions (audio rooms with N×M streams per participant).
Perf #10 — Streams list view:
QuicConnection maintains a parallel insertion-ordered List<QuicStream>
alongside the streams Map. Writer's round-robin scan reads the list
directly instead of allocating `entries.toList()` per drain.
No removal path exists today; the insert points (openBidi/UniStream,
getOrCreatePeerStreamLocked) update both.
AckTrackerGatingTest pins the new gating contract: first build returns
a frame; second build without new reception returns null; subsequent
ack-eliciting reception re-arms; non-ack-eliciting receptions alone
don't.
https://claude.ai/code/session_01EC1tfXfap8k8GyKvrxkxZx
Claude
920b36cdd6