[StatsPlugin] Add API to check if an instrument is enabled (#36757)

Closes #36757

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/36757 from yashykt:CheckIfMetricsAreEnabled 7755e98e60
PiperOrigin-RevId: 639067118

src/core/telemetry/metrics.h

@@ -329,6 +329,9 @@ class StatsPlugin {
   // Removes a callback previously added via AddCallback().  The stats
   // plugin may not use the callback after this method returns.
   virtual void RemoveCallback(RegisteredMetricCallback* callback) = 0;
+  // Returns true if instrument \a handle is enabled.
+  virtual bool IsInstrumentEnabled(
+      GlobalInstrumentsRegistry::GlobalInstrumentHandle handle) = 0;
 
   // Gets a ClientCallTracer associated with this stats plugin which can be used
   // in a call.
@@ -424,6 +427,17 @@ class GlobalStatsPluginRegistry {
                                       optional_values);
       }
     }
+    // Returns true if any of the stats plugins in the group have enabled \a
+    // handle.
+    bool IsInstrumentEnabled(
+        GlobalInstrumentsRegistry::GlobalInstrumentHandle handle) {
+      for (auto& state : plugins_state_) {
+        if (state.plugin->IsInstrumentEnabled(handle)) {
+          return true;
+        }
+      }
+      return false;
+    }
 
     // Registers a callback to be used to populate callback metrics.
     // The callback will update the specified metrics.  The callback

src/cpp/ext/otel/otel_plugin.cc

@@ -913,6 +913,12 @@ grpc_core::ServerCallTracer* OpenTelemetryPlugin::GetServerCallTracer(
               scope_config));
 }
 
+bool OpenTelemetryPlugin::IsInstrumentEnabled(
+    grpc_core::GlobalInstrumentsRegistry::GlobalInstrumentHandle handle) {
+  return !absl::holds_alternative<Disabled>(
+      instruments_data_.at(handle.index).instrument);
+}
+
 }  // namespace internal
 
 constexpr absl::string_view

src/cpp/ext/otel/otel_plugin.h

@@ -404,6 +404,9 @@ class OpenTelemetryPlugin : public grpc_core::StatsPlugin {
   grpc_core::ServerCallTracer* GetServerCallTracer(
       std::shared_ptr<grpc_core::StatsPlugin::ScopeConfig> scope_config)
       override;
+  bool IsInstrumentEnabled(
+      grpc_core::GlobalInstrumentsRegistry::GlobalInstrumentHandle handle)
+      override;
 
   const absl::AnyInvocable<bool(const grpc_core::ChannelArgs& /*args*/) const>&
   server_selector() const {

test/core/test_util/fake_stats_plugin.h

@@ -210,7 +210,8 @@ class FakeStatsPlugin : public StatsPlugin {
           bool(const experimental::StatsPluginChannelScope& /*scope*/) const>
           channel_filter = nullptr,
       bool use_disabled_by_default_metrics = false)
-      : channel_filter_(std::move(channel_filter)) {
+      : channel_filter_(std::move(channel_filter)),
+        use_disabled_by_default_metrics_(use_disabled_by_default_metrics) {
     GlobalInstrumentsRegistry::ForEach(
         [&](const GlobalInstrumentsRegistry::GlobalInstrumentDescriptor&
                 descriptor) {
@@ -359,6 +360,12 @@ class FakeStatsPlugin : public StatsPlugin {
       std::shared_ptr<StatsPlugin::ScopeConfig> /*scope_config*/) override {
     return nullptr;
   }
+  bool IsInstrumentEnabled(
+      GlobalInstrumentsRegistry::GlobalInstrumentHandle handle) override {
+    const auto& descriptor =
+        GlobalInstrumentsRegistry::GetInstrumentDescriptor(handle);
+    return use_disabled_by_default_metrics_ || descriptor.enable_by_default;
+  }
 
   absl::optional<uint64_t> GetUInt64CounterValue(
       GlobalInstrumentsRegistry::GlobalInstrumentHandle handle,
@@ -600,6 +607,7 @@ class FakeStatsPlugin : public StatsPlugin {
   absl::AnyInvocable<bool(
       const experimental::StatsPluginChannelScope& /*scope*/) const>
       channel_filter_;
+  bool use_disabled_by_default_metrics_;
   // Instruments.
   Mutex mu_;
   absl::flat_hash_map<uint32_t, Counter<uint64_t>> uint64_counters_

test/cpp/ext/otel/otel_plugin_test.cc

@@ -39,6 +39,7 @@
 
 #include "src/core/lib/config/core_configuration.h"
 #include "src/core/telemetry/call_tracer.h"
+#include "test/core/test_util/fake_stats_plugin.h"
 #include "test/core/test_util/test_config.h"
 #include "test/cpp/end2end/test_service_impl.h"
 #include "test/cpp/ext/otel/otel_test_library.h"
@@ -1281,7 +1282,17 @@ TEST_F(OpenTelemetryPluginOptionEnd2EndTest,
   EXPECT_EQ(absl::get<std::string>(server_attributes.at("key5")), "value5");
 }
 
-using OpenTelemetryPluginNPCMetricsTest = OpenTelemetryPluginEnd2EndTest;
+class OpenTelemetryPluginNPCMetricsTest
+    : public OpenTelemetryPluginEnd2EndTest {
+ protected:
+  void TearDown() override {
+    // We are tearing down OpenTelemetryPluginEnd2EndTest first to ensure that
+    // gRPC has shutdown before we reset the instruments registry.
+    OpenTelemetryPluginEnd2EndTest::TearDown();
+    grpc_core::GlobalInstrumentsRegistryTestPeer::
+        ResetGlobalInstrumentsRegistry();
+  }
+};
 
 TEST_F(OpenTelemetryPluginNPCMetricsTest, RecordUInt64Counter) {
   constexpr absl::string_view kMetricName = "uint64_counter";
@@ -1677,6 +1688,28 @@ TEST_F(OpenTelemetryPluginNPCMetricsTest,
                                 ::testing::DoubleEq(kMax), kCount))))));
 }
 
+TEST_F(OpenTelemetryPluginNPCMetricsTest, InstrumentsEnabledTest) {
+  constexpr absl::string_view kDoubleHistogramMetricName =
+      "yet_another_yet_another_double_histogram";
+  constexpr absl::string_view kUnit64CounterMetricName = "uint64_counter";
+  auto histogram_handle =
+      grpc_core::GlobalInstrumentsRegistry::RegisterDoubleHistogram(
+          kDoubleHistogramMetricName, "A simple double histogram.", "unit",
+          /*enable_by_default=*/false)
+          .Build();
+  auto counter_handle =
+      grpc_core::GlobalInstrumentsRegistry::RegisterUInt64Counter(
+          kUnit64CounterMetricName, "A simple unit64 counter.", "unit",
+          /*enable_by_default=*/false)
+          .Build();
+  Init(std::move(Options().set_metric_names({kDoubleHistogramMetricName})));
+  auto stats_plugins =
+      grpc_core::GlobalStatsPluginRegistry::GetStatsPluginsForServer(
+          grpc_core::ChannelArgs());
+  EXPECT_TRUE(stats_plugins.IsInstrumentEnabled(histogram_handle));
+  EXPECT_FALSE(stats_plugins.IsInstrumentEnabled(counter_handle));
+}
+
 using OpenTelemetryPluginCallbackMetricsTest = OpenTelemetryPluginEnd2EndTest;
 
 // The callback minimal interval is longer than the OT reporting interval, so we