make span remember the SpanProcessor it was created with

Author: Hailios

sdk/src/trace/span.cc

@@ -89,7 +89,11 @@ Span::Span(std::shared_ptr<Tracer> &&tracer,
   recordable_->SetStartTime(NowOr(options.start_system_time));
   start_steady_time = NowOr(options.start_steady_time);
   recordable_->SetResource(tracer_->GetResource());
-  tracer_->GetProcessor().OnStart(*recordable_, parent_span_context);
+
+  // store the span processor, this is important to use the same processor even
+  // in case the tracer changes from single processor to a MultiSpanProcessor
+  span_processor_ = &tracer_->GetProcessor();
+  span_processor_->OnStart(*recordable_, parent_span_context);
 }
 
 Span::~Span()
@@ -203,6 +207,8 @@ void Span::End(const opentelemetry::trace::EndSpanOptions &options) noexcept
 {
   std::lock_guard<std::mutex> lock_guard{mu_};
 
+  // has_ended_ could be removed and instead rely on span_processor_,
+  // resetting it after calling OnEnd. it would save 8 bytes in each Span object.
   if (has_ended_ == true)
   {
     return;
@@ -218,7 +224,7 @@ void Span::End(const opentelemetry::trace::EndSpanOptions &options) noexcept
   recordable_->SetDuration(std::chrono::steady_clock::time_point(end_steady_time) -
                            std::chrono::steady_clock::time_point(start_steady_time));
 
-  tracer_->GetProcessor().OnEnd(std::move(recordable_));
+  span_processor_->OnEnd(std::move(recordable_));
   recordable_.reset();
 }
 

sdk/src/trace/span.h

@@ -79,11 +79,12 @@ class Span final : public opentelemetry::trace::Span
   }
 
 private:
-  std::shared_ptr<Tracer> tracer_;
+  std::shared_ptr<Tracer> tracer_; // also keeps span_processor_ alive
   mutable std::mutex mu_;
   std::unique_ptr<Recordable> recordable_;
   opentelemetry::common::SteadyTimestamp start_steady_time;
   std::unique_ptr<opentelemetry::trace::SpanContext> span_context_;
+  SpanProcessor * span_processor_{nullptr}; // kept alive by tracer_
   bool has_ended_{false};
 };
 }  // namespace trace