channel.go
func (ccc channelConnectionCommon) Tracer() opentracing.Tracer {
	if ccc.tracer != nil {
		return ccc.tracer
	}
	return opentracing.GlobalTracer()
}
func (ccc channelConnectionCommon) Tracer() opentracing.Tracer {
	if ccc.tracer != nil {
		return ccc.tracer
	}
	return opentracing.GlobalTracer()
}
// Tracer returns the OpenTracing Tracer for this channel. If no tracer was provided
// in the configuration, returns opentracing.GlobalTracer(). Note that this approach
// allows opentracing.GlobalTracer() to be initialized _after_ the channel is created.