Context(), Tracer() aren't taking the lock

[RaduBerinde]

func (s *spanImpl) Tracer() opentracing.Tracer {
    return s.tracer
}

func (s *spanImpl) Context() opentracing.SpanContext {
    return s.raw.Context
}

These functions are not taking their locks. Context() could happen concurrently to e.g. a SetBaggageItem call. For Tracer() it's less clear if it should take the lock, as it is immutable except for the DebugAssertUseAfterFinish case:

    if s.tracer.options.DebugAssertUseAfterFinish {
        // This makes it much more likely to catch a panic on any subsequent
        // operation since s.tracer is accessed on every call to `Lock`.
        // We don't call `reset()` here to preserve the logs in the Span
        // which are printed when the assertion triggers.
        s.tracer = nil
    }

It's a question of whether we want data races to show up in that case (in addition to panics). BTW I don't understand the "s.tracer is accessed on every call to Lock" part in that comment, it doesn't seem true.
@tschottdorf

[bhs]

The Context() case is a bug... it was previously a pointer that was immutable during the Span lifetime. The Tracer() case seems ok to me as-is, though. I am being lazy and haven't checked whether Tracer() is called while the lock is held or not...