[BUG] fatal error: concurrent map writes (*span).SetAttributes

[theFong]

Version of dd-trace-go

v1.59.0

Describe what happened:

Calling span.SetAttributes concurrently results in fatal error: concurrent map writes

Describe what you expected:
The span does not seem thread-safe for concurrent reads and writes and it is unclear whether this is the intended behavior.

Steps to reproduce the issue:

	ctx, span = tracer.Start(ctx, "test")
	defer span.End()

	numberOfWorkers := 100
	workerIDs := []int{}
	for i := 0; i < numberOfWorkers; i++ {
		workerIDs = append(workerIDs, i)
	}
	_, err = collections.ParallelWorkerMapE(workerIDs, func(i int) (any, error) { // this is a custom method that loops over a slice and runs a function in parallel
		for {
			span.SetAttributes(attribute.Float64("workerID", float64(i)))
		}
	}, numberOfWorkers)
	if !assert.NoError(t, err) {
		return
	}

Additional environment details (Version of Go, Operating System, etc.):
go version go1.20 linux/amd64

[darccio]

Reproduced:

func TestConcurrentSetAttributes(t *testing.T) {
	tp := NewTracerProvider()
	otel.SetTracerProvider(tp)
	tr := otel.Tracer("")

	_, span := tr.Start(context.Background(), "test")
	defer span.End()

	var wg sync.WaitGroup
	for i := 0; i < 100; i++ {
		wg.Add(1)
		i := i
		go func(val int) {
			defer wg.Done()
			span.SetAttributes(attribute.Float64("workerID", float64(i)))
		}(i)
	}
}

[darccio]

Released as part of v1.60.1 cc @theFong