example of #2946

main.go

package main

import (
	"context"
	"fmt"

	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/exporters/stdout/stdouttrace"
	"go.opentelemetry.io/otel/sdk/trace"

	"golang.org/x/sync/errgroup"
)

func main() {
	exp, _ := stdouttrace.New()
	tp := trace.NewTracerProvider(
		trace.WithSpanProcessor(trace.NewSimpleSpanProcessor(exp)),
	)
	otel.SetTracerProvider(tp)

	ctx, cancel := context.WithCancel(context.Background())

	ctx, span := otel.Tracer("app").Start(ctx, "parent")
	defer span.End()
	eg, ctx := errgroup.WithContext(ctx)

	subspans := make([]struct{}, 100)

	for j := range subspans {
		idx := j
		eg.Go(func() error {
			_, subSpan := otel.Tracer("app").Start(ctx, fmt.Sprintf("subtree_%d", idx))
			defer subSpan.End()
			// fmt.Printf("subtree_%d\n", idx)
			cancel()
			return fmt.Errorf("stuff")
		})
	}

	eg.Wait()
}