add otel instrumentation (#581)

this change adds OTEL tracing to a few places

* Top-level application lifecycle (config/init/cleanup, main loop)
* http.sys requests

it also brings some otlptrace optimizations and dynamic configuration of tracing. OTLP tracing is currently always disabled

1 files changed, 37 insertions, 23 deletions

diff --git a/src/zentelemetry/otlptrace.cpp b/src/zentelemetry/otlptrace.cpp
index b634eacf6..f987afcfe 100644
--- a/src/zentelemetry/otlptrace.cpp
+++ b/src/zentelemetry/otlptrace.cpp
@@ -7,6 +7,7 @@
 
 #	include <zencore/endian.h>
 #	include <zencore/memory/memoryarena.h>
+#	include <zencore/scopeguard.h>
 #	include <zencore/session.h>
 #	include <zencore/testing.h>
 #	include <zencore/uid.h>
@@ -106,16 +107,15 @@ Span::~Span()
 void
 Span::End()
 {
-	if (m_Ended)
+	if (m_EndTime)
 	{
 		return;
 	}
 
-	ZEN_ASSERT(t_TraceState.ActiveSpan == this);
+	ZEN_ASSERT_SLOW(t_TraceState.ActiveSpan == this);
 
-	m_Ended					= true;
-	t_TraceState.ActiveSpan = m_ParentSpan;
 	m_EndTime				= NowInNanoseconds();
+	t_TraceState.ActiveSpan = m_ParentSpan;
 }
 
 Span*
@@ -127,10 +127,10 @@ Span::GetCurrentSpan()
 SpanId
 Span::GetCurrentSpanId(TraceId& OutTraceId)
 {
-	if (t_TraceState.ActiveSpan)
+	if (const auto& State = t_TraceState; State.ActiveSpan)
 	{
-		OutTraceId = t_TraceState.CurrentTraceId;
-		return t_TraceState.ActiveSpan->m_SpanId;
+		OutTraceId = State.CurrentTraceId;
+		return State.ActiveSpan->m_SpanId;
 	}
 	else
 	{
@@ -271,6 +271,14 @@ IsRecording()
 
 //////////////////////////////////////////////////////////////////////////
 
+std::atomic<bool> g_OtlpTraceEnabled{false};
+
+inline bool
+IsOtlpTraceEnabled()
+{
+	return g_OtlpTraceEnabled.load();
+}
+
 thread_local Tracer* t_Tracer;
 
 struct Tracer::Impl
@@ -325,22 +333,19 @@ Tracer::GetTracer()
 ScopedSpan
 Tracer::CreateSpan(std::string_view Name)
 {
-	Tracer* TracerPtr = GetTracer();
-
-	Impl* const ImplPtr = TracerPtr->m_Impl;
-
-	Span* NewSpan = new (ImplPtr->m_Arena) Span(ImplPtr->m_Arena, Name, ImplPtr->m_SpanChain);
-
-	ImplPtr->m_SpanChain = NewSpan;
-	ImplPtr->m_SpanCount.fetch_add(1);
-
-	return ScopedSpan(NewSpan, TracerPtr);
+	return ScopedSpan(Name);
 }
 
 //////////////////////////////////////////////////////////////////////////
 
 ScopedSpan::ScopedSpan(std::string_view Name)
 {
+	if (!IsOtlpTraceEnabled())
+	{
+		// m_Tracer and m_Span remain null
+		return;
+	}
+
 	Tracer* TracerPtr = Tracer::GetTracer();
 
 	Tracer::Impl* const ImplPtr = TracerPtr->m_Impl;
@@ -379,15 +384,24 @@ otlptrace_forcelink()
 
 TEST_CASE("otlp.trace")
 {
+	// Enable OTLP tracing for the duration of this test
+	auto _ = MakeGuard([PreviousState = zen::otel::g_OtlpTraceEnabled.load()]() { zen::otel::g_OtlpTraceEnabled.store(PreviousState); });
+	zen::otel::g_OtlpTraceEnabled.store(true);
+
 	{
-		ScopedSpan Span = Tracer::CreateSpan("span0");
-		Span->AddEvent("TestEvent1"sv);
-		Span->AddEvent("TestEvent2"sv);
+		ScopedSpan Span0("span0", [](Span& S) {
+			S.AddAttribute("attr1"sv, "value1"sv);
+			S.AddAttribute("attr2"sv, 42ULL);
+			S.AddEvent("TestEvent1"sv);
+			S.AddEvent("TestEvent2"sv);
+		});
 
 		{
-			ScopedSpan Span2 = Tracer::CreateSpan("span1");
-			Span2->AddEvent("TestEvent3"sv);
-			Span2->AddEvent("TestEvent4"sv);
+			ScopedSpan Span1 = Tracer::CreateSpan("span1");
+			Span1.WithSpan([](Span& S) {
+				S.AddEvent("TestEvent3"sv);
+				S.AddEvent("TestEvent4"sv);
+			});
 		}
 	}
 }