Reduce TWCC sender allocations#426
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## main #426 +/- ##
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- Coverage 80.13% 80.09% -0.04%
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Files 88 88
Lines 4617 4623 +6
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+ Hits 3700 3703 +3
- Misses 735 736 +1
- Partials 182 184 +2
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Record stored the unwrapped sequence number by taking its address, which heap-allocates the local on every call, whether or not the branch is taken. Updates now go through a setter that writes into a single reused allocation. addReceived allocated one rtcp.RecvDelta per received packet. Store values and build the pointer slice once per feedback in getRTCP. BenchmarkRecord: 21.1ns/op 1 alloc -> 6.9ns/op 0 allocs. BenchmarkRecordAndBuildFeedbackPacket (100 packets per feedback): 4546ns/op 322 allocs -> 2270ns/op 21 allocs.
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Recorder.Recordheap-allocates on every call: it stores the unwrapped sequence number intostartSequenceNumberby taking the address of a local, which moves the local to the heap whether or not the branch is taken. SinceRecordruns once per received RTP packet, this costs one allocation per packet. Updates now go through a setter that writes into a single reused allocation.feedback.addReceivedalso allocated one*rtcp.RecvDeltaper received packet. Deltas are now accumulated by value, and the[]*rtcp.RecvDeltathat the rtcp API requires is materialized once per feedback packet ingetRTCP, which hands ownership of the backing array to the packet.No exported API or behavior changes.
Benchmarks (added in this PR, run on main vs this branch on a M2 MacBook Air; the second records 100 packets per feedback):
BenchmarkRecordBenchmarkRecordAndBuildFeedbackPacketTestRecordDoesNotAllocateInSteadyStatepins the steady-stateRecordpath at zero allocations.