Pass telemetry directly to the Controller

[MrAlias]

Do not enqueue telemetry to a channel just to dequeue it and send it to the Controller.

This requires that the Controller.Trace method is concurrent safe. The Controller is updated and tests are added to ensure this is the case.

Benchmark

package chbench

import (
	"sync/atomic"
	"testing"
)

func Benchmark(b *testing.B) {
	b.Run("Channel", func(b *testing.B) {
		var out atomic.Int64
		process := func(i int) { out.Store(int64(i)) }

		ch := make(chan int)
		go func() {
			for i := range ch {
				process(i)
			}
		}()

		b.ResetTimer()
		for n := 0; n < b.N; n++ {
			ch <- n
			for int(out.Load()) != n {
			}
		}
	})
	b.Run("Direct", func(b *testing.B) {
		var out atomic.Int64
		process := func(i int) { out.Store(int64(i)) }

		b.ResetTimer()
		for n := 0; n < b.N; n++ {
			process(n)
			for int(out.Load()) != n {
			}
		}
	})
}

$ go test . -count=10 -bench=. > out.txt && benchstat out.txt
goos: linux
goarch: amd64
pkg: testing/chbench
cpu: Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz
           │   out.txt   │
           │   sec/op    │
/Channel-8   31.39µ ± 4%
/Direct-8    8.325n ± 1%
geomean      511.2n

[damemi]

lgtm, just curious @MrAlias could you explain more what you did to make the controller concurrent-safe?

[MrAlias]

lgtm, just curious @MrAlias could you explain more what you did to make the controller concurrent-safe?

The controller's Trace method was calling getTracer which accessed a single tracer map. That map was not guarded by any semaphore and had data-races when accessed concurrently. This removes that code and instead uses the concurrent safe TracerProvider.Tracer method directly.

The default implementation of the SDK already provides a concurrent-safe cached lookup of a Tracer: https://github.com/open-telemetry/opentelemetry-go/blob/030ffdf4e46a496d0aa4693d488f8b5e534fd9bc/sdk/trace/provider.go#L125-L175. This switches to just using that instead of recreating.