[GitHub] [arrow] lidavidm commented on a change in pull request #12609: ARROW-15067: [C++] Add tracing spans to the scanner

[GitBox <gi...@apache.org>]

lidavidm commented on a change in pull request #12609:
URL: https://github.com/apache/arrow/pull/12609#discussion_r840735194



##########
File path: cpp/src/arrow/util/tracing_internal.h
##########
@@ -101,6 +86,33 @@ AsyncGenerator<T> WrapAsyncGenerator(AsyncGenerator<T> wrapped,
   };
 }
 
+/// \brief Propagate the given span to each invocation of an async generator.
+template <typename T>
+AsyncGenerator<T> PropagateSpanThroughAsyncGenerator(
+    AsyncGenerator<T> wrapped,
+    opentelemetry::nostd::shared_ptr<opentelemetry::trace::Span> span) {
+  return [=]() mutable -> Future<T> {
+    auto scope = GetTracer()->WithActiveSpan(span);
+    return wrapped();
+  };
+}
+
+/// \brief Propagate the currently active span to each invocation of an async generator.
+template <typename T>
+AsyncGenerator<T> PropagateSpanThroughAsyncGenerator(AsyncGenerator<T> wrapped) {
+  auto span = GetTracer()->GetCurrentSpan();
+  if (!span->GetContext().IsValid()) return wrapped;
+  return PropagateSpanThroughAsyncGenerator(std::move(wrapped), std::move(span));
+}
+
+/*
+ * PropagateSpanThroughAsyncGenerator - only makes sure the trace context is propagated,
+ * so that spans created when running generator instances asynchronously do not
+ * end up in a separate, disconnected trace.
+ * WrapAsyncGenerator - Connect the current span to the generator. When the generator
+ * finishes, it will stop the span. Optionally, create child spans at each invocation.

Review comment:
       These could probably be folded into the docstrings themselves?

##########
File path: cpp/src/arrow/dataset/file_ipc.cc
##########
@@ -121,6 +137,10 @@ Result<std::shared_ptr<Schema>> IpcFileFormat::Inspect(const FileSource& source)
 Result<RecordBatchGenerator> IpcFileFormat::ScanBatchesAsync(
     const std::shared_ptr<ScanOptions>& options,
     const std::shared_ptr<FileFragment>& file) const {
+#ifdef ARROW_WITH_OPENTELEMETRY
+  auto tracer = arrow::internal::tracing::GetTracer();
+  auto parent_span = tracer->GetCurrentSpan();
+#endif

Review comment:
       Does this actually have an effect anymore?




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