From 7b0a1897d10f954a0e276ad003a345a0b64269eb Mon Sep 17 00:00:00 2001
From: JBD <jbd@golang.org>
Date: Wed, 18 Apr 2018 12:53:52 -0700
Subject: [PATCH] Create Go execution tracer task for each span

This allows us to associate OpenCensus spans with execution
tracer tasks and allow users to have fine-grained details
about the runtime events happened in the lifetime of a
distributed tracing span.
---
 trace/trace.go         | 12 ++++++++++--
 trace/trace_go11.go    | 26 ++++++++++++++++++++++++++
 trace/trace_nongo11.go | 25 +++++++++++++++++++++++++
 3 files changed, 61 insertions(+), 2 deletions(-)
 create mode 100644 trace/trace_go11.go
 create mode 100644 trace/trace_nongo11.go

diff --git a/trace/trace.go b/trace/trace.go
index 58932badc..785699139 100644
--- a/trace/trace.go
+++ b/trace/trace.go
@@ -43,7 +43,9 @@ type Span struct {
 	spanContext SpanContext
 	// spanStore is the spanStore this span belongs to, if any, otherwise it is nil.
 	*spanStore
-	exportOnce sync.Once
+	endOnce sync.Once
+
+	executionTracerSpanEnd func() // ends the execution tracer span
 }
 
 // IsRecordingEvents returns true if events are being recorded for this span.
@@ -162,6 +164,9 @@ func StartSpan(ctx context.Context, name string, o ...StartOption) (context.Cont
 		op(&opts)
 	}
 	span := startSpanInternal(name, parent != SpanContext{}, parent, false, opts)
+
+	ctx, end := startExecutionTracerSpan(ctx, name)
+	span.executionTracerSpanEnd = end
 	return NewContext(ctx, span), span
 }
 
@@ -175,6 +180,8 @@ func StartSpanWithRemoteParent(ctx context.Context, name string, parent SpanCont
 		op(&opts)
 	}
 	span := startSpanInternal(name, parent != SpanContext{}, parent, true, opts)
+	ctx, end := startExecutionTracerSpan(ctx, name)
+	span.executionTracerSpanEnd = end
 	return NewContext(ctx, span), span
 }
 
@@ -258,7 +265,8 @@ func (s *Span) End() {
 	if !s.IsRecordingEvents() {
 		return
 	}
-	s.exportOnce.Do(func() {
+	s.endOnce.Do(func() {
+		s.executionTracerSpanEnd()
 		// TODO: optimize to avoid this call if sd won't be used.
 		sd := s.makeSpanData()
 		sd.EndTime = internal.MonotonicEndTime(sd.StartTime)
diff --git a/trace/trace_go11.go b/trace/trace_go11.go
new file mode 100644
index 000000000..2c0996d17
--- /dev/null
+++ b/trace/trace_go11.go
@@ -0,0 +1,26 @@
+// Copyright 2018, OpenCensus Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build go1.11
+
+package trace
+
+import (
+	"context"
+	t "runtime/trace"
+)
+
+func startExecutionTracerSpan(ctx context.Context, name string) (context.Context, func()) {
+	return t.NewContext(ctx, name)
+}
diff --git a/trace/trace_nongo11.go b/trace/trace_nongo11.go
new file mode 100644
index 000000000..64406e18c
--- /dev/null
+++ b/trace/trace_nongo11.go
@@ -0,0 +1,25 @@
+// Copyright 2018, OpenCensus Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build !go1.11
+
+package trace
+
+import (
+	"context"
+)
+
+func startExecutionTracerSpan(ctx context.Context, name string) (context.Context, func()) {
+	return ctx, func() {}
+}