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feat: Publish OTel process context #324

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0e050b6
Import process context reference implementation
ivoanjo Jun 4, 2026
2db7a35
feat: [PROF-14789] Publish OTel process context
ivoanjo Jun 4, 2026
6813769
Make autoformatter happy
ivoanjo Jun 5, 2026
35bb013
Tweak to make CI happy
ivoanjo Jun 5, 2026
76267e5
Another try at making CI happy
ivoanjo Jun 5, 2026
71d7825
More small tweaks to make CI happy
ivoanjo Jun 5, 2026
bcda89d
More CI fixes
ivoanjo Jun 5, 2026
38359e2
More making CI happy
ivoanjo Jun 5, 2026
1690f10
Add links to where `otel_process_ctx.h/.cpp
ivoanjo Jun 8, 2026
4f6916d
Introduce new constant with library name, rather than hardcoding in r…
ivoanjo Jun 18, 2026
afddc6d
Minor: Remove redundant includes
ivoanjo Jun 18, 2026
8b9a8a3
Minor: Use references when building up metadata
ivoanjo Jun 18, 2026
c191436
Minor: Don't compare unordered maps as it can easily break
ivoanjo Jun 18, 2026
9d050df
Tweak behavior when report_hostname is disabled + add test
ivoanjo Jun 19, 2026
ab0b053
Add missing `static` declaration
ivoanjo Jun 19, 2026
2984054
Minor: Fix wording in comment to use infinitive
ivoanjo Jun 19, 2026
c561524
Introduce move-only RAII guard and mutex to ensure correctness
ivoanjo Jun 19, 2026
0575cde
Tighten tests for moving the tracer instance
ivoanjo Jun 19, 2026
e2ab668
Merge branch 'main' into ivoanjo/prof-14789-otel-process-ctx
ivoanjo Jun 22, 2026
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4 changes: 4 additions & 0 deletions BUILD.bazel
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Original file line number Diff line number Diff line change
Expand Up @@ -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",
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2 changes: 2 additions & 0 deletions CMakeLists.txt
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Expand Up @@ -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
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13 changes: 13 additions & 0 deletions include/datadog/tracer.h
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Expand Up @@ -33,6 +33,7 @@ class TraceSampler;
class SpanSampler;
class IDGenerator;
class InMemoryFile;
class OtelCtxGuard;

class Tracer {
std::shared_ptr<Logger> logger_;
Expand All @@ -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_guard_;
Baggage::Options baggage_opts_;
bool baggage_injection_enabled_;
bool baggage_extraction_enabled_;
Expand All @@ -65,6 +68,16 @@ class Tracer {
Tracer(const FinalizedTracerConfig& config,
const std::shared_ptr<const IDGenerator>& generator);

~Tracer();

@xlamorlette-datadog xlamorlette-datadog Jun 8, 2026

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Declaring a user-defined destructor suppresses the implicit move constructor and move assignment.

Moreover, the implicit copy is now problematic because it will lead to several calls to otel_process_ctx_drop_current(). More precisely, the problem is that:

  • otel_process_ctx_publish() is called from the constructor (via store_config(), line 228);
  • otel_process_ctx_drop_current() is called in then destructor (line 124).

They operate on a process-global singleton (published_state in otel_process_ctx.cpp). So the destructor's drop is global, and it fires for every Tracer instance destroyed, including copies and temporaries.

This notably breaks the implementation of nginx-datadog that uses move and return by value on Tracer.

I suggest adding a move-only RAII guard, held by a unique_ptr, so that to transfer the ownership on move. Copy constructor and assignment should be deleted. This is just an idea, maybe a better solution could come from thinking about the whole Otel process context handling.

By the way, TEST_TRACER("move semantics"), line 1885 of test_tracer.cpp is wrong: when the move constructor doesn't exist, it binds to the copy constructor. This test should be fixed!

@ivoanjo ivoanjo Jun 19, 2026

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Ughhh thanks for spotting this, my C++-fu is not strong enough to have spotted this one.

In c561524 I've added a guard and a mutex that enforces thread-safe last-writer-wins semantics for the process context.

And in 0575cde I've tightened the "move semantics" test to not surprise us again in the future.


// 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();
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3 changes: 3 additions & 0 deletions include/datadog/version.h
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Expand Up @@ -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.
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5 changes: 3 additions & 2 deletions src/datadog/error.cpp
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@@ -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 {
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