[SDK] Tracer::StartSpan benchmark and optimizations

CHANGELOG.md

@@ -41,6 +41,9 @@ Breaking changes:
 
 ## [1.28.0] 2026-07-16
 
+* [SDK] Add Tracer::StartSpan benchmark and optimizations
+  [#4248](https://github.com/open-telemetry/opentelemetry-cpp/pull/4248)
+
 * [RELEASE] Bump main branch to 1.28.0-dev
   [#4081](https://github.com/open-telemetry/opentelemetry-cpp/pull/4081)
 

api/include/opentelemetry/trace/context.h

@@ -27,13 +27,14 @@ inline nostd::shared_ptr<Span> GetSpan(const context::Context &context) noexcept
 // stored directly in the context, and returns an invalid SpanContext if neither is present.
 inline SpanContext GetSpanContext(const context::Context &context) noexcept
 {
-  if (!context.HasKey(kSpanKey))
+  const context::ContextValue context_value = context.GetValue(kSpanKey);
+
+  if (nostd::holds_alternative<nostd::monostate>(context_value))
   {
+    // The context does not have a span or span context
     return SpanContext::GetInvalid();
   }
 
-  const context::ContextValue context_value = context.GetValue(kSpanKey);
-
   // Get the span metadata from the active span in the context.
   if (const nostd::shared_ptr<Span> *maybe_span =
           nostd::get_if<nostd::shared_ptr<Span>>(&context_value))

api/include/opentelemetry/trace/default_span.h

@@ -14,7 +14,7 @@ namespace trace
 {
 
 /**
- * DefaultSpan provides a non-operational Span that propagates
+ * DefaultSpan provides a non-recording Span that propagates
  * the tracer context by wrapping it inside the Span object.
  */
 
@@ -28,6 +28,7 @@ class DefaultSpan : public Span
 
   trace::SpanContext GetContext() const noexcept override { return span_context_; }
 
+  // Returns false, as DefaultSpan is a non-recording span.
   bool IsRecording() const noexcept override { return false; }
 
   void SetAttribute(nostd::string_view /* key */,

api/include/opentelemetry/trace/span_startoptions.h

@@ -59,7 +59,7 @@ struct StartSpanOptions
   // - 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();
+  nostd::variant<SpanContext, context::Context> parent = context::Context{};
 
   // TODO:
   // SpanContext remote_parent;

opentracing-shim/test/shim_utils_test.cc

@@ -26,6 +26,7 @@
 #include "opentelemetry/common/attribute_value.h"
 #include "opentelemetry/common/key_value_iterable.h"
 #include "opentelemetry/common/timestamp.h"
+#include "opentelemetry/context/context.h"
 #include "opentelemetry/context/runtime_context.h"
 #include "opentelemetry/nostd/function_ref.h"
 #include "opentelemetry/nostd/shared_ptr.h"
@@ -34,13 +35,13 @@
 #include "opentelemetry/opentracingshim/shim_utils.h"
 #include "opentelemetry/opentracingshim/span_context_shim.h"
 #include "opentelemetry/trace/span_context.h"
+#include "opentelemetry/trace/span_metadata.h"
 #include "opentelemetry/trace/span_startoptions.h"
 
-#include "shim_mocks.h"
-
 namespace trace_api = opentelemetry::trace;
 namespace baggage   = opentelemetry::baggage;
 namespace common    = opentelemetry::common;
+namespace context   = opentelemetry::context;
 namespace nostd     = opentelemetry::nostd;
 namespace shim      = opentelemetry::opentracingshim;
 
@@ -138,8 +139,7 @@ TEST(ShimUtilsTest, MakeOptionsShim_EmptyRefs)
             common::SystemTimestamp{options.start_system_timestamp});
   ASSERT_EQ(options_shim.start_steady_time,
             common::SteadyTimestamp{options.start_steady_timestamp});
-  ASSERT_EQ(nostd::get<trace_api::SpanContext>(options_shim.parent),
-            trace_api::SpanContext::GetInvalid());
+  ASSERT_FALSE(nostd::get<context::Context>(options_shim.parent).HasKey(trace_api::kSpanKey));
 }
 
 TEST(ShimUtilsTest, MakeOptionsShim_InvalidSpanContext)
@@ -154,8 +154,8 @@ TEST(ShimUtilsTest, MakeOptionsShim_InvalidSpanContext)
             common::SystemTimestamp{options.start_system_timestamp});
   ASSERT_EQ(options_shim.start_steady_time,
             common::SteadyTimestamp{options.start_steady_timestamp});
-  ASSERT_EQ(nostd::get<trace_api::SpanContext>(options_shim.parent),
-            trace_api::SpanContext::GetInvalid());
+
+  ASSERT_FALSE(nostd::get<context::Context>(options_shim.parent).HasKey(trace_api::kSpanKey));
 }
 
 TEST(ShimUtilsTest, MakeOptionsShim_FirstChildOf)

sdk/include/opentelemetry/sdk/trace/sampler.h

@@ -58,11 +58,11 @@ struct SamplingResult
   //  The tracestate used by the span.
   nostd::shared_ptr<opentelemetry::trace::TraceState> trace_state;
 
-  inline bool IsRecording()
+  inline bool IsRecording() const noexcept
   {
     return decision == Decision::RECORD_ONLY || decision == Decision::RECORD_AND_SAMPLE;
   }
-  inline bool IsSampled() { return decision == Decision::RECORD_AND_SAMPLE; }
+  inline bool IsSampled() const noexcept { return decision == Decision::RECORD_AND_SAMPLE; }
 };
 
 /**

sdk/include/opentelemetry/sdk/trace/tracer.h

@@ -141,6 +141,7 @@ class Tracer final : public opentelemetry::trace::Tracer,
 #if OPENTELEMETRY_ABI_VERSION_NO < 2
   std::atomic<bool> is_enabled_{false};
 #endif
+  nostd::shared_ptr<opentelemetry::trace::Span> noop_span_;
 };
 }  // namespace trace
 }  // namespace sdk

sdk/src/trace/span.cc

@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0
 
 #include <chrono>
+#include <map>
 #include <utility>
 
 #include "opentelemetry/nostd/function_ref.h"
@@ -55,8 +56,9 @@ Span::Span(std::shared_ptr<Tracer> &&tracer,
            const common::KeyValueIterable &attributes,
            const opentelemetry::trace::SpanContextKeyValueIterable &links,
            const opentelemetry::trace::StartSpanOptions &options,
+           const opentelemetry::sdk::trace::SamplingResult &sampling_result,
            const opentelemetry::trace::SpanContext &parent_span_context,
-           std::unique_ptr<opentelemetry::trace::SpanContext> span_context) noexcept
+           opentelemetry::trace::SpanContext span_context) noexcept
     : tracer_{std::move(tracer)},
       recordable_{tracer_->GetProcessor().MakeRecordable()},
       start_steady_time{options.start_steady_time},
@@ -69,11 +71,11 @@ Span::Span(std::shared_ptr<Tracer> &&tracer,
   recordable_->SetSpanLimits(tracer_->GetSpanLimits());
   recordable_->SetName(name);
   recordable_->SetInstrumentationScope(tracer_->GetInstrumentationScope());
-  recordable_->SetIdentity(*span_context_, parent_span_context.IsValid()
-                                               ? parent_span_context.span_id()
-                                               : opentelemetry::trace::SpanId());
+  recordable_->SetIdentity(span_context_, parent_span_context.IsValid()
+                                              ? parent_span_context.span_id()
+                                              : opentelemetry::trace::SpanId());
 
-  recordable_->SetTraceFlags(span_context_->trace_flags());
+  recordable_->SetTraceFlags(span_context_.trace_flags());
 
   attributes.ForEachKeyValue([&](nostd::string_view key, common::AttributeValue value) noexcept {
     recordable_->SetAttribute(key, value);
@@ -86,6 +88,14 @@ Span::Span(std::shared_ptr<Tracer> &&tracer,
     return true;
   });
 
+  if (sampling_result.attributes != nullptr)
+  {
+    for (const auto &kv : *sampling_result.attributes)
+    {
+      recordable_->SetAttribute(kv.first, kv.second);
+    }
+  }
+
   recordable_->SetSpanKind(options.kind);
   recordable_->SetStartTime(NowOr(options.start_system_time));
   start_steady_time = NowOr(options.start_steady_time);

sdk/src/trace/span.h

@@ -11,6 +11,7 @@
 #include "opentelemetry/common/timestamp.h"
 #include "opentelemetry/nostd/string_view.h"
 #include "opentelemetry/sdk/trace/recordable.h"
+#include "opentelemetry/sdk/trace/sampler.h"
 #include "opentelemetry/sdk/trace/tracer.h"
 #include "opentelemetry/trace/span.h"
 #include "opentelemetry/trace/span_context.h"
@@ -31,8 +32,9 @@ class Span final : public opentelemetry::trace::Span
        const opentelemetry::common::KeyValueIterable &attributes,
        const opentelemetry::trace::SpanContextKeyValueIterable &links,
        const opentelemetry::trace::StartSpanOptions &options,
+       const opentelemetry::sdk::trace::SamplingResult &sampling_result,
        const opentelemetry::trace::SpanContext &parent_span_context,
-       std::unique_ptr<opentelemetry::trace::SpanContext> span_context) noexcept;
+       opentelemetry::trace::SpanContext span_context) noexcept;
 
   Span(const Span &)            = delete;
   Span(Span &&)                 = delete;
@@ -73,17 +75,14 @@ class Span final : public opentelemetry::trace::Span
 
   bool IsRecording() const noexcept override;
 
-  opentelemetry::trace::SpanContext GetContext() const noexcept override
-  {
-    return *span_context_.get();
-  }
+  opentelemetry::trace::SpanContext GetContext() const noexcept override { return span_context_; }
 
 private:
   std::shared_ptr<Tracer> tracer_;
   mutable std::mutex mu_;
   std::unique_ptr<Recordable> recordable_;
   opentelemetry::common::SteadyTimestamp start_steady_time;
-  std::unique_ptr<opentelemetry::trace::SpanContext> span_context_;
+  opentelemetry::trace::SpanContext span_context_;
   bool has_ended_{false};
 };
 }  // namespace trace