Parent-or-else Sampler (#142)

sdk/include/opentelemetry/sdk/trace/samplers/parent_or_else.h

@@ -0,0 +1,57 @@
+#pragma once
+
+#include "opentelemetry/sdk/common/atomic_shared_ptr.h"
+#include "opentelemetry/sdk/trace/sampler.h"
+
+OPENTELEMETRY_BEGIN_NAMESPACE
+namespace sdk
+{
+namespace trace
+{
+namespace trace_api = opentelemetry::trace;
+
+/**
+ * A placeholder class that stores the states of a span.
+ * Will be replaced by the real SpanContext class once it is implemented.
+ */
+class Sampler::SpanContext
+{
+public:
+  inline explicit SpanContext(bool is_recording, bool sampled_flag)
+      : is_recording(is_recording), sampled_flag(sampled_flag)
+  {}
+
+  bool is_recording;
+  bool sampled_flag;
+};
+
+/**
+ * The parent or else sampler is a composite sampler. ParentOrElse(delegateSampler) either respects
+ * the parent span's sampling decision or delegates to delegateSampler for root spans.
+ */
+class ParentOrElseSampler : public Sampler
+{
+public:
+  explicit ParentOrElseSampler(std::shared_ptr<Sampler> delegate_sampler) noexcept;
+  /** The decision either respects the parent span's sampling decision or delegates to
+   * delegateSampler for root spans
+   * @return Returns NOT_RECORD always
+   */
+  SamplingResult ShouldSample(const SpanContext * parent_context,
+                              trace_api::TraceId trace_id,
+                              nostd::string_view name,
+                              trace_api::SpanKind span_kind,
+                              const trace_api::KeyValueIterable & attributes) noexcept override;
+
+  /**
+   * @return Description MUST be ParentOrElse{delegate_sampler_.getDescription()}
+   */
+  std::string GetDescription() const noexcept override;
+
+private:
+  const std::shared_ptr<Sampler> delegate_sampler_;
+  const std::string description_;
+};
+}  // namespace trace
+}  // namespace sdk
+OPENTELEMETRY_END_NAMESPACE

sdk/src/trace/CMakeLists.txt

@@ -1 +1 @@
-add_library(opentelemetry_trace tracer_provider.cc tracer.cc span.cc)
+add_library(opentelemetry_trace tracer_provider.cc tracer.cc span.cc samplers/parent_or_else.cc)

sdk/src/trace/samplers/parent_or_else.cc

@@ -0,0 +1,41 @@
+#include "opentelemetry/sdk/trace/samplers/parent_or_else.h"
+
+OPENTELEMETRY_BEGIN_NAMESPACE
+namespace sdk
+{
+namespace trace
+{
+ParentOrElseSampler::ParentOrElseSampler(std::shared_ptr<Sampler> delegate_sampler) noexcept
+    : delegate_sampler_(delegate_sampler),
+      description_("ParentOrElse{" + delegate_sampler->GetDescription() + "}")
+{}
+
+SamplingResult ParentOrElseSampler::ShouldSample(
+    const SpanContext *parent_context,
+    trace_api::TraceId trace_id,
+    nostd::string_view name,
+    trace_api::SpanKind span_kind,
+    const trace_api::KeyValueIterable &attributes) noexcept
+{
+  if (parent_context == nullptr)
+  {
+    // If no parent (root span) exists returns the result of the delegateSampler
+    return delegate_sampler_->ShouldSample(parent_context, trace_id, name, span_kind, attributes);
+  }
+  
+  // If parent exists:
+  if (parent_context->sampled_flag)
+  {
+    return {Decision::RECORD_AND_SAMPLE, nullptr};
+  }
+
+  return {Decision::NOT_RECORD, nullptr};
+}
+
+std::string ParentOrElseSampler::GetDescription() const noexcept
+{
+  return description_;
+}
+}  // namespace trace
+}  // namespace sdk
+OPENTELEMETRY_END_NAMESPACE

sdk/test/trace/BUILD

@@ -53,8 +53,6 @@ cc_test(
     ],
 )
 
-
-
 cc_test(
     name = "always_off_sampler_test",
     srcs = [
@@ -64,4 +62,15 @@ cc_test(
         "//sdk/src/trace",
         "@com_google_googletest//:gtest_main",
     ],
-)
+)
+
+cc_test(
+    name = "parent_or_else_sampler_test",
+    srcs = [
+        "parent_or_else_sampler_test.cc",
+    ],
+    deps = [
+        "//sdk/src/trace",
+        "@com_google_googletest//:gtest_main",
+    ],
+)

sdk/test/trace/CMakeLists.txt

@@ -1,5 +1,6 @@
 foreach(testname tracer_provider_test span_data_test simple_processor_test
-                 tracer_test always_off_sampler_test always_on_sampler_test)
+                 tracer_test always_off_sampler_test always_on_sampler_test 
+                 parent_or_else_sampler_test)
   add_executable(${testname} "${testname}.cc")
   target_link_libraries(${testname} ${GTEST_BOTH_LIBRARIES}
                         ${CMAKE_THREAD_LIBS_INIT} opentelemetry_trace)

sdk/test/trace/parent_or_else_sampler_test.cc

@@ -0,0 +1,50 @@
+#include <gtest/gtest.h>
+#include <memory>
+#include "opentelemetry/sdk/trace/samplers/always_off.h"
+#include "opentelemetry/sdk/trace/samplers/always_on.h"
+#include "opentelemetry/sdk/trace/samplers/parent_or_else.h"
+
+using opentelemetry::sdk::trace::AlwaysOffSampler;
+using opentelemetry::sdk::trace::AlwaysOnSampler;
+using opentelemetry::sdk::trace::Decision;
+using opentelemetry::sdk::trace::ParentOrElseSampler;
+
+TEST(ParentOrElseSampler, ShouldSample)
+{
+  ParentOrElseSampler sampler_off(std::make_shared<AlwaysOffSampler>());
+  ParentOrElseSampler sampler_on(std::make_shared<AlwaysOnSampler>());
+
+  // Set up parameters
+  opentelemetry::trace::TraceId trace_id;
+  opentelemetry::trace::SpanKind span_kind = opentelemetry::trace::SpanKind::kInternal;
+  using M = std::map<std::string, int>;
+  M m1 = {{}};
+  opentelemetry::trace::KeyValueIterableView<M> view{m1};
+  opentelemetry::sdk::trace::Sampler::SpanContext parent_context_sampled(true, true);
+  opentelemetry::sdk::trace::Sampler::SpanContext parent_context_nonsampled(true, false);
+
+  // Case 1: Parent doesn't exist. Return result of delegateSampler()
+  auto sampling_result = sampler_off.ShouldSample(nullptr, trace_id, "", span_kind, view);
+  auto sampling_result2 = sampler_on.ShouldSample(nullptr, trace_id, "", span_kind, view);
+
+  ASSERT_EQ(Decision::NOT_RECORD, sampling_result.decision);
+  ASSERT_EQ(Decision::RECORD_AND_SAMPLE, sampling_result2.decision);
+
+  // Case 2: Parent exists and SampledFlag is true
+  auto sampling_result3 =
+      sampler_off.ShouldSample(&parent_context_sampled, trace_id, "", span_kind, view);
+  ASSERT_EQ(Decision::RECORD_AND_SAMPLE, sampling_result3.decision);
+
+  // Case 3: Parent exists and SampledFlag is false
+  auto sampling_result4 =
+      sampler_on.ShouldSample(&parent_context_nonsampled, trace_id, "", span_kind, view);
+  ASSERT_EQ(Decision::NOT_RECORD, sampling_result4.decision);
+}
+
+TEST(ParentOrElseSampler, GetDescription)
+{
+  ParentOrElseSampler sampler(std::make_shared<AlwaysOffSampler>());
+  ASSERT_EQ("ParentOrElse{AlwaysOffSampler}", sampler.GetDescription());
+  ParentOrElseSampler sampler2(std::make_shared<AlwaysOnSampler>());
+  ASSERT_EQ("ParentOrElse{AlwaysOnSampler}", sampler2.GetDescription());
+}