[API] Create root span with active span

api/include/opentelemetry/trace/context.h

@@ -23,6 +23,16 @@ inline nostd::shared_ptr<Span> GetSpan(const context::Context &context) noexcept
  return nostd::shared_ptr<Span>(new DefaultSpan(SpanContext::GetInvalid()));
 }
 
+inline bool IsRootSpan(const context::Context &context) noexcept
+{
+ context::ContextValue is_root_span = context.GetValue(kIsRootSpanKey);
+ if (nostd::holds_alternative<bool>(is_root_span))
+ {
+ return nostd::get<bool>(is_root_span);
+ }
+ return false;
+}
+
 // Set Span into explicit context
 inline context::Context SetSpan(context::Context &context, nostd::shared_ptr<Span> span) noexcept
 {

api/include/opentelemetry/trace/span_metadata.h

@@ -20,7 +20,8 @@ enum class SpanKind
 };
 
 // The key identifies the active span in the current context.
-constexpr char kSpanKey[] = "active_span";
+constexpr char kSpanKey[] = "active_span";
+constexpr char kIsRootSpanKey[] = "is_root_span";
 
 // StatusCode - Represents the canonical set of status codes of a finished Span.
 enum class StatusCode

api/include/opentelemetry/trace/span_startoptions.h

@@ -34,8 +34,31 @@ struct StartSpanOptions
 
  // Explicitly set the parent of a Span.
  //
- // This defaults to an invalid span context. In this case, the Span is
- // automatically parented to the currently active span.
+ // The `parent` field is designed to establish parent-child relationships
+ // in tracing spans. It can be set to either a `SpanContext` or a
+ // `context::Context` object.
+ //
+ // - When set to valid `SpanContext`, it directly assigns a specific Span as the parent
+ // of the newly created Span.
+ //
+ // - Alternatively, setting the `parent` field to a `context::Context` allows for
+ // more nuanced parent identification:
+ // 1. If the `Context` contains a Span object, this Span is treated as the parent.
+ // 2. If the `Context` contains the boolean flag `is_root_span` set to `true`,
+ // it indicates that the new Span should be treated as a root Span, i.e., it
+ // does not have a parent Span.
+ // Example Usage:
+ // ```cpp
+ // trace_api::StartSpanOptions options;
+ // opentelemetry::context::Context root;
+ // root = root.SetValue(kIsRootSpanKey, true);
+ // options.parent = root;
+ // auto root_span = tracer->StartSpan("span root", options);
+ // ```
+ //
+ // - If the `parent` field is not set, the newly created Span will inherit the
+ // parent of the currently active Span (if any) in the current context.
+ //
  nostd::variant<SpanContext, context::Context> parent = SpanContext::GetInvalid();
 
  // TODO:

sdk/src/trace/tracer.cc

@@ -43,6 +43,13 @@ nostd::shared_ptr<opentelemetry::trace::Span> Tracer::StartSpan(
  {
  parent_context = span_context;
  }
+ else
+ {
+ if (opentelemetry::trace::IsRootSpan(context))
+ {
+ parent_context = opentelemetry::trace::SpanContext{false, false};
+ }
+ }
  }
 
  opentelemetry::trace::TraceId trace_id;

sdk/test/trace/tracer_test.cc

@@ -1008,6 +1008,26 @@ TEST(Tracer, WithActiveSpan)
  spans = span_data->GetSpans();
  ASSERT_EQ(1, spans.size());
  EXPECT_EQ("span 2", spans.at(0)->GetName());
+ EXPECT_EQ(spans.at(0).get()->GetParentSpanId(), span_first->GetContext().span_id());
+ EXPECT_EQ(spans.at(0).get()->GetTraceId(), span_first->GetContext().trace_id());
+
+ {
+ trace_api::StartSpanOptions options;
+ opentelemetry::context::Context c1;
+ c1 = c1.SetValue(opentelemetry::trace::kIsRootSpanKey, true);
+ options.parent = c1;
+ auto root_span = tracer->StartSpan("span root", options);
+
+ spans = span_data->GetSpans();
+ ASSERT_EQ(0, spans.size());
+
+ root_span->End();
+ }
+ spans = span_data->GetSpans();
+ ASSERT_EQ(1, spans.size());
+ EXPECT_EQ("span root", spans.at(0)->GetName());
+ EXPECT_EQ(spans.at(0).get()->GetParentSpanId(), opentelemetry::trace::SpanId());
+ EXPECT_NE(spans.at(0).get()->GetTraceId(), span_first->GetContext().trace_id());
 
  span_first->End();
  }