conn: skip timeout callbacks for background contexts#566
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Every frame read and write registered a context.AfterFunc callback so a context cancellation could close the connection. context.Background cannot be canceled because its Done channel is nil, but the code still constructed, stored, stopped, and cleared a callback registration for each operation. Skip that work when ctx.Done() is nil, and only clear a timeout when one was actually installed. BenchmarkConn also joins its writer goroutine after timing so repeated benchmark runs finish cleanly. The results below compare parent 7039364 with this commit on an Apple M4 Max using GOMAXPROCS=1 over 10 samples. A temporary in-package harness, not included in this commit, repeatedly called one internal frame read using either context.Background or an uncanceled context.WithCancel. Header reads parse a minimal frame header; payload reads copy 512 bytes from a buffered repeating reader. Before this change, setupReadTimeout called context.AfterFunc even for context.Background. Avoiding that dead registration reduces background header reads from 121.95 to 29.94 ns/op and payload reads from 124.17 to 29.15 ns/op. Both fall from 152 B/op and 4 allocs/op to zero. Cancelable contexts still need an AfterFunc registration, so they remain at 152 B/op and 4 allocs/op. BenchmarkConn/disabledCompress uses a cancelable context as well, so it remains at 1219 B/op and 32 allocs/op.
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kylecarbs
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Skip per-operation timeout callback setup when the context cannot be canceled, such as
context.Background().Timeout setup now reports whether it installed a callback, so callers only clear callbacks that exist. The benchmark also joins its writer goroutine to make repeated runs reliable.
Previously, reads and writes called
context.AfterFuncfor every operation, even whenctx.Done()wasnil. This had a measurable cost.Similar to #565, I know this is a micro-optimization, but its basic and understandable and it produced measurable results in some of my actual workloads that were cheap!
Benchmarks
Each operation avoids 4 allocations and 152 bytes from the unnecessary
context.AfterFuncregistration.Cancelable contexts are unchanged because they still require a cancellation callback. Accordingly,
BenchmarkConn/disabledCompress, which uses a cancelable context, showed no statistically significant change.