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Did you change your mind about releasing this to v4? :) Main is v5 |
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My local branch got into a weird state. I'll re-apply to v4 after. |
Loop.Err is a non-blocking select on the done channel, which Go
compiles to a runtime.selectnbrecv call that cannot be inlined away.
Conn.Write and Conn.Read call it once per packet, so it is measurable
on packet-heavy workloads: it accounted for 5% of flat CPU in a profile
of an SFU fanning video to ~7k subscribers.
Add Loop.Closed, an atomic load that mirrors done and inlines into its
callers, and use it to gate the Conn.Read, Conn.Write and
Conn.WriteToPair error paths and the Loop.Run fast path. The flag is
stored after done is closed, so Closed always implies Err is non-nil
and the callers can keep reporting Err itself. Err and Done are
untouched and remain the exact context.Context implementation, both
reading only the done channel.
BenchmarkErr-10 4.65 ns/op
BenchmarkClosed-10 2.13 ns/op
goos: darwin, goarch: arm64, cpu: Apple M1 Pro
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## main #1018 +/- ##
==========================================
- Coverage 91.90% 91.88% -0.02%
==========================================
Files 46 46
Lines 5510 5511 +1
==========================================
Hits 5064 5064
- Misses 446 447 +1
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Loop.Err is a non-blocking select on the done channel, which Go compiles to a runtime.selectnbrecv call that cannot be inlined away. Conn.Write and Conn.Read call it once per packet, so it is measurable on packet-heavy workloads: it accounted for 5% of flat CPU in a profile of an SFU fanning video to ~7k subscribers.
Add Loop.Closed, an atomic load that mirrors done and inlines into its callers, and use it to gate the Conn.Read, Conn.Write and Conn.WriteToPair error paths and the Loop.Run fast path. The flag is stored after done is closed, so Closed always implies Err is non-nil and the callers can keep reporting Err itself. Err and Done are untouched and remain the exact context.Context implementation, both reading only the done channel.
goos: darwin, goarch: arm64, cpu: Apple M1 Pro
Description
Reference issue
Fixes #...