feat: Publish OTel process context

BUILD.bazel

@@ -39,6 +39,10 @@ cc_library(
         "src/datadog/msgpack.cpp",
         "src/datadog/msgpack.h",
         "src/datadog/null_logger.h",
+        "src/datadog/otel_process_ctx.cpp",
+        "src/datadog/otel_process_ctx.h",
+        "src/datadog/otel_process_ctx_guard.cpp",
+        "src/datadog/otel_process_ctx_guard.h",
         "src/datadog/parse_util.cpp",
         "src/datadog/parse_util.h",
         "src/datadog/platform_util.h",

CMakeLists.txt

@@ -194,6 +194,8 @@ target_sources(dd-trace-cpp-objects
     src/datadog/limiter.cpp
     src/datadog/logger.cpp
     src/datadog/msgpack.cpp
+    src/datadog/otel_process_ctx.cpp
+    src/datadog/otel_process_ctx_guard.cpp
     src/datadog/parse_util.cpp
     src/datadog/propagation_style.cpp
     src/datadog/random.cpp

include/datadog/tracer.h

@@ -33,6 +33,7 @@ class TraceSampler;
 class SpanSampler;
 class IDGenerator;
 class InMemoryFile;
+class OtelCtxGuard;
 
 class Tracer {
   std::shared_ptr<Logger> logger_;
@@ -51,6 +52,8 @@ class Tracer {
   // read to determine if the process is instrumented with a tracer and to
   // retrieve relevant tracing information.
   std::shared_ptr<InMemoryFile> metadata_file_;
+  // Owns the published OpenTelemetry process context, if any.
+  std::unique_ptr<OtelCtxGuard> otel_context_guard_;
   Baggage::Options baggage_opts_;
   bool baggage_injection_enabled_;
   bool baggage_extraction_enabled_;
@@ -65,6 +68,16 @@ class Tracer {
   Tracer(const FinalizedTracerConfig& config,
          const std::shared_ptr<const IDGenerator>& generator);
 
+  ~Tracer();
+
+  // Move-only. The otel context guarded by OtelCtxGuard is a process-wide
+  // singleton; duplicating ownership would lead to spurious drops, so copies
+  // are disallowed.
+  Tracer(Tracer&&) noexcept;
+  Tracer& operator=(Tracer&&) noexcept;
+  Tracer(const Tracer&) = delete;
+  Tracer& operator=(const Tracer&) = delete;
+
   // Create a new trace and return the root span of the trace. Optionally
   // specify a `config` indicating the attributes of the root span.
   Span create_span();

include/datadog/version.h

@@ -4,6 +4,9 @@
 
 namespace datadog::tracing {
 
+// This library's name
+extern const char *const tracer_library_name;
+
 // The release version at or before this code revision, e.g. "v0.1.12".
 // That is, this code is at least as recent as `tracer_version`, but may be
 // more recent.

src/datadog/error.cpp

@@ -1,13 +1,14 @@
 #include <datadog/error.h>
+#include <datadog/version.h>
 
 #include <ostream>
 
 namespace datadog {
 namespace tracing {
 
 std::ostream& operator<<(std::ostream& stream, const Error& error) {
-  return stream << "[dd-trace-cpp error code " << int(error.code) << "] "
-                << error.message;
+  return stream << "[" << tracer_library_name << " error code "
+                << int(error.code) << "] " << error.message;
 }
 
 Error Error::with_prefix(StringView prefix) const {