From 4dc403c05751f5f9a8829c18e08c4e9a91a3fa2c Mon Sep 17 00:00:00 2001
From: "Amr Hanafi (MAHDI))" <amrh@microsoft.com>
Date: Thu, 30 Jan 2020 13:55:39 -0800
Subject: [PATCH 1/3] Add AlwaysParentSample

---
 sdk/trace/sampling.go      |  7 ++++++
 sdk/trace/sampling_test.go | 49 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+)
 create mode 100644 sdk/trace/sampling_test.go

diff --git a/sdk/trace/sampling.go b/sdk/trace/sampling.go
index 736752367da..f33810c97a3 100644
--- a/sdk/trace/sampling.go
+++ b/sdk/trace/sampling.go
@@ -77,3 +77,10 @@ func NeverSample() Sampler {
 		return SamplingDecision{Sample: false}
 	}
 }
+
+// AlwaysParentSample returns a Sampler that samples only if the parent span is sampled.
+func AlwaysParentSample() Sampler {
+	return func(p SamplingParameters) SamplingDecision {
+		return SamplingDecision{Sample: p.ParentContext.IsSampled()}
+	}
+}
diff --git a/sdk/trace/sampling_test.go b/sdk/trace/sampling_test.go
new file mode 100644
index 00000000000..7c86ed0b716
--- /dev/null
+++ b/sdk/trace/sampling_test.go
@@ -0,0 +1,49 @@
+// Copyright 2019, OpenTelemetry 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.
+
+package trace_test
+
+import (
+	"testing"
+
+	"go.opentelemetry.io/otel/api/core"
+	sdktrace "go.opentelemetry.io/otel/sdk/trace"
+)
+
+func TestAlwaysParentSampleWithParentSampled(t *testing.T) {
+	sampler := sdktrace.AlwaysParentSample()
+	traceID, _ := core.TraceIDFromHex("4bf92f3577b34da6a3ce929d0e0e4736")
+	spanID, _ := core.SpanIDFromHex("00f067aa0ba902b7")
+	parentCtx := core.SpanContext{
+		TraceID:    traceID,
+		SpanID:     spanID,
+		TraceFlags: core.TraceFlagsSampled,
+	}
+	if !sampler(sdktrace.SamplingParameters{ParentContext: parentCtx}).Sample {
+		t.Error("Sampling decision should be true")
+	}
+}
+
+func TestAlwaysParentSampleWithParentNotSampled(t *testing.T) {
+	sampler := sdktrace.AlwaysParentSample()
+	traceID, _ := core.TraceIDFromHex("4bf92f3577b34da6a3ce929d0e0e4736")
+	spanID, _ := core.SpanIDFromHex("00f067aa0ba902b7")
+	parentCtx := core.SpanContext{
+		TraceID: traceID,
+		SpanID:  spanID,
+	}
+	if sampler(sdktrace.SamplingParameters{ParentContext: parentCtx}).Sample {
+		t.Error("Sampling decision should be false")
+	}
+}

From cd50ca1095cd9f9ea14dc0068a6a806f03d13c58 Mon Sep 17 00:00:00 2001
From: Amr Hanafi <amramahdi@gmail.com>
Date: Fri, 31 Jan 2020 09:45:57 -0800
Subject: [PATCH 2/3] Update sampler doc

Co-Authored-By: Krzesimir Nowak <qdlacz@gmail.com>
---
 sdk/trace/sampling.go | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/sdk/trace/sampling.go b/sdk/trace/sampling.go
index f33810c97a3..03a73d88ee3 100644
--- a/sdk/trace/sampling.go
+++ b/sdk/trace/sampling.go
@@ -78,7 +78,8 @@ func NeverSample() Sampler {
 	}
 }
 
-// AlwaysParentSample returns a Sampler that samples only if the parent span is sampled.
+// AlwaysParentSample returns a Sampler that samples a trace only
+// if the parent span is sampled.
 func AlwaysParentSample() Sampler {
 	return func(p SamplingParameters) SamplingDecision {
 		return SamplingDecision{Sample: p.ParentContext.IsSampled()}

From 943a9a68de7522c074653a1684e2542945bc97ce Mon Sep 17 00:00:00 2001
From: "Amr Hanafi (MAHDI))" <amrh@microsoft.com>
Date: Fri, 31 Jan 2020 23:51:50 -0800
Subject: [PATCH 3/3] Address PR comments

---
 sdk/trace/sampling.go      | 6 +++---
 sdk/trace/sampling_test.go | 2 +-
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/sdk/trace/sampling.go b/sdk/trace/sampling.go
index 03a73d88ee3..4f91d4d95c6 100644
--- a/sdk/trace/sampling.go
+++ b/sdk/trace/sampling.go
@@ -80,8 +80,8 @@ func NeverSample() Sampler {
 
 // AlwaysParentSample returns a Sampler that samples a trace only
 // if the parent span is sampled.
+// This Sampler is a passthrough to the ProbabilitySampler with
+// a fraction of value 0.
 func AlwaysParentSample() Sampler {
-	return func(p SamplingParameters) SamplingDecision {
-		return SamplingDecision{Sample: p.ParentContext.IsSampled()}
-	}
+	return ProbabilitySampler(0)
 }
diff --git a/sdk/trace/sampling_test.go b/sdk/trace/sampling_test.go
index 7c86ed0b716..488bfe946ef 100644
--- a/sdk/trace/sampling_test.go
+++ b/sdk/trace/sampling_test.go
@@ -1,4 +1,4 @@
-// Copyright 2019, OpenTelemetry Authors
+// Copyright 2020, OpenTelemetry Authors
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.