runtime: lock-free channels

[dvyukov]

Here is design doc:
https://docs.google.com/document/d/1yIAYmbvL3JxOKOjuCyon7JhW4cSv1wy5hC0ApeGMV9s/pub

Here is the implementation:
https://golang.org/cl/12544043/

I've benchmarked the change of a real app where chans were abandoned in favor of other
sync primitives due to perf reasons:
https://groups.google.com/d/msg/golang-dev/0IElw_BbTrk/cGHMdNoHGQEJ
and the change provides 23% end-to-end speedup making chans significantly faster than
the other synchronization.

[olekukonko]

What is the update on this ?

[odeke-em]

Unfortunately the CL seems to have gone stale @dvyukov due to changes to runtime's code.

[OneOfOne]

I have implemented an extremely simple lock-free channel here, if there's interest, I'm willing to implement it in the runtime and submit a CL (and re-license it under the Go license of course).

➜ go test -bench=. -benchmem -cpu 1,4,8,32 -benchtime 3s

#   ch := NewSize(runtime.NumCPU())
BenchmarkLFChan         30000000               168 ns/op              40 B/op          4 allocs/op
BenchmarkLFChan-4       30000000               175 ns/op              45 B/op          4 allocs/op
BenchmarkLFChan-8       20000000               205 ns/op              45 B/op          4 allocs/op
BenchmarkLFChan-32      20000000               201 ns/op              45 B/op          4 allocs/op

# ch := make(chan interface{}, runtime.NumCPU())
BenchmarkChan           50000000               115 ns/op               8 B/op          1 allocs/op
BenchmarkChan-4         20000000               261 ns/op               8 B/op          1 allocs/op
BenchmarkChan-8         20000000               331 ns/op               8 B/op          1 allocs/op
BenchmarkChan-32        10000000               532 ns/op               8 B/op          1 allocs/op

PASS
ok      github.com/OneOfOne/lfchan      51.663s

[OneOfOne]

@dvyukov @ianlancetaylor @rsc

[dvyukov]

@OneOfOne The tricky part will be to support blocking on empty/full chan and select statements.
Also your chan does not seem to be FIFO which is a requirement.
Also you scan the whole array to find an item, this can be very expensive for large chans.