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context: Consider disable Type.comparable check in WithValue #47741

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morlay opened this issue Aug 17, 2021 · 1 comment
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context: Consider disable Type.comparable check in WithValue #47741

morlay opened this issue Aug 17, 2021 · 1 comment
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@morlay
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morlay commented Aug 17, 2021 •
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What version of Go are you using (go version)?

$ go version
1.15 1.16 1.17

What did you do?

When I use context.WithValue(), I see it always cost 20ns/op +
I checked the source codes, i found a TypeOf(key).Comparable() https://github.com/golang/go/blob/master/src/context/context.go#L530,

Then i remove it, WithValue become faster

see the Benchmark results below

$ go test -test.bench=BenchmarkWithValue -test.benchmem ./...
goos: darwin
goarch: arm64
pkg: github.com/go-courier/x/contextx
BenchmarkWithValue/WithValue_with_reflect_type_comparable_check-8               50766240                23.37 ns/op           48 B/op          1 allocs/op
BenchmarkWithValue/WithValue_without_reflect_type_comparable_check-8            1000000000               0.3160 ns/op          0 B/op          0 allocs/op

Maybe we could consider to remove https://github.com/golang/go/blob/master/src/context/context.go#L530

Or just make valuectx public for people to recreate a faster WithValue
@seankhliao
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If the value isn't comparable then there would be no way to retrieve it.
Ensuring that the program runs correctly should be more important.
See the change that added it: https://go-review.googlesource.com/c/go/+/21799/

context.Context is an interface and people are free to create other implementations with less safety.

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@morlay @gopherbot @seankhliao