[SDK] Add meter scope configurator

CHANGELOG.md

@@ -21,6 +21,9 @@ Increment the:
 * [SDK] Support OTEL_SDK_DISABLED environment variable
   [#3245](https://github.com/open-telemetry/opentelemetry-cpp/pull/3245)
 
+* [SDK] Add meter scope configurator
+  [#3268](https://github.com/open-telemetry/opentelemetry-cpp/pull/3268)
+
 Important changes:
 
 * [SDK] Support OTEL_SDK_DISABLED environment variable

sdk/include/opentelemetry/sdk/metrics/meter.h

@@ -19,6 +19,7 @@
 #include "opentelemetry/sdk/instrumentationscope/instrumentation_scope.h"
 #include "opentelemetry/sdk/metrics/instrument_metadata_validator.h"
 #include "opentelemetry/sdk/metrics/instruments.h"
+#include "opentelemetry/sdk/metrics/meter_config.h"
 #include "opentelemetry/sdk/metrics/meter_context.h"
 #include "opentelemetry/sdk/metrics/state/async_metric_storage.h"
 #include "opentelemetry/sdk/resource/resource.h"
@@ -138,12 +139,15 @@ class Meter final : public opentelemetry::metrics::Meter
   // Mapping between instrument-name and Aggregation Storage.
   std::unordered_map<std::string, std::shared_ptr<MetricStorage>> storage_registry_;
   std::shared_ptr<ObservableRegistry> observable_registry_;
+  MeterConfig meter_config_;
   std::unique_ptr<SyncWritableMetricStorage> RegisterSyncMetricStorage(
       InstrumentDescriptor &instrument_descriptor);
   std::unique_ptr<AsyncWritableMetricStorage> RegisterAsyncMetricStorage(
       InstrumentDescriptor &instrument_descriptor);
   opentelemetry::common::SpinLockMutex storage_lock_;
 
+  static opentelemetry::metrics::NoopMeter kNoopMeter;
+
   static nostd::shared_ptr<opentelemetry::metrics::ObservableInstrument>
   GetNoopObservableInsrument()
   {

sdk/include/opentelemetry/sdk/metrics/meter_config.h

@@ -0,0 +1,59 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+#pragma once
+
+#include "opentelemetry/version.h"
+
+OPENTELEMETRY_BEGIN_NAMESPACE
+namespace sdk
+{
+namespace metrics
+{
+/**
+ * MeterConfig defines various configurable aspects of a Meter's behavior.
+ * This class should not be used directly to configure a Meter's behavior, instead a
+ * ScopeConfigurator should be used to compute the desired MeterConfig which can then be used to
+ * configure a Meter.
+ */
+class MeterConfig
+{
+public:
+  bool operator==(const MeterConfig &other) const noexcept;
+
+  /**
+   * Returns if the Meter is enabled or disabled. Meters are enabled by default.
+   * @return a boolean indicating if the Meter is enabled. Defaults to true.
+   */
+  bool IsEnabled() const noexcept;
+
+  /**
+   * Returns a MeterConfig that represents a disabled Meter. A disabled meter behaves like a
+   * no-op meter.
+   * @return a static constant MeterConfig that represents a disabled meter.
+   */
+  static MeterConfig Disabled();
+
+  /**
+   * Returns a MeterConfig that represents an enabled Meter.
+   * @return a static constant MeterConfig that represents an enabled meter.
+   */
+  static MeterConfig Enabled();
+
+  /**
+   * Returns a MeterConfig that represents a Meter configured with the default behavior.
+   * The default behavior is guided by the OpenTelemetry specification.
+   * @return a static constant MeterConfig that represents a meter configured with default
+   * behavior.
+   */
+  static MeterConfig Default();
+
+private:
+  explicit MeterConfig(const bool disabled = false) : disabled_(disabled) {}
+  bool disabled_;
+  static const MeterConfig kDefaultConfig;
+  static const MeterConfig kDisabledConfig;
+};
+}  // namespace metrics
+}  // namespace sdk
+OPENTELEMETRY_END_NAMESPACE

sdk/include/opentelemetry/sdk/metrics/meter_context.h

@@ -13,6 +13,8 @@
 #include "opentelemetry/nostd/function_ref.h"
 #include "opentelemetry/nostd/span.h"
 #include "opentelemetry/nostd/string_view.h"
+#include "opentelemetry/sdk/instrumentationscope/scope_configurator.h"
+#include "opentelemetry/sdk/metrics/meter_config.h"
 #include "opentelemetry/sdk/metrics/metric_reader.h"
 #include "opentelemetry/sdk/metrics/state/metric_collector.h"
 #include "opentelemetry/sdk/metrics/view/instrument_selector.h"
@@ -48,14 +50,17 @@ class MeterContext : public std::enable_shared_from_this<MeterContext>
 public:
   /**
    * Initialize a new meter provider
-   * @param readers The readers to be configured with meter context.
    * @param views The views to be configured with meter context.
    * @param resource  The resource for this meter context.
    */
   MeterContext(
       std::unique_ptr<ViewRegistry> views = std::unique_ptr<ViewRegistry>(new ViewRegistry()),
       const opentelemetry::sdk::resource::Resource &resource =
-          opentelemetry::sdk::resource::Resource::Create({})) noexcept;
+          opentelemetry::sdk::resource::Resource::Create({}),
+      std::unique_ptr<instrumentationscope::ScopeConfigurator<MeterConfig>> meter_configurator =
+          std::make_unique<instrumentationscope::ScopeConfigurator<MeterConfig>>(
+              instrumentationscope::ScopeConfigurator<MeterConfig>::Builder(MeterConfig::Default())
+                  .Build())) noexcept;
 
   /**
    * Obtain the resource associated with this meter context.
@@ -70,13 +75,19 @@ class MeterContext : public std::enable_shared_from_this<MeterContext>
   ViewRegistry *GetViewRegistry() const noexcept;
 
   /**
-   * NOTE - INTERNAL method, can change in future.
+   * Obtain the ScopeConfigurator with this meter context.
+   * @return The ScopeConfigurator for this meter context.
+   */
+  const instrumentationscope::ScopeConfigurator<MeterConfig> &GetMeterConfigurator() const noexcept;
+
+  /**
+   * NOTE - INTERNAL method, can change in the future.
    * Process callback for each meter in thread-safe manner
    */
   bool ForEachMeter(nostd::function_ref<bool(std::shared_ptr<Meter> &meter)> callback) noexcept;
 
   /**
-   * NOTE - INTERNAL method, can change in future.
+   * NOTE - INTERNAL method, can change in the future.
    * Get the configured meters.
    * This method is NOT thread safe, and only called through MeterProvider
    *
@@ -154,6 +165,7 @@ class MeterContext : public std::enable_shared_from_this<MeterContext>
   std::vector<std::shared_ptr<CollectorHandle>> collectors_;
   std::unique_ptr<ViewRegistry> views_;
   opentelemetry::common::SystemTimestamp sdk_start_ts_;
+  std::unique_ptr<instrumentationscope::ScopeConfigurator<MeterConfig>> meter_configurator_;
   std::vector<std::shared_ptr<Meter>> meters_;
 
 #ifdef ENABLE_METRICS_EXEMPLAR_PREVIEW

sdk/include/opentelemetry/sdk/metrics/meter_context_factory.h

@@ -23,15 +23,39 @@ class OPENTELEMETRY_EXPORT MeterContextFactory
 {
 public:
   /**
-   * Create a MeterContext.
+   * Create a MeterContext with valid defaults.
+   * @return A unique pointer to the created MeterContext object.
    */
   static std::unique_ptr<MeterContext> Create();
 
+  /**
+   * Create a MeterContext with specified views.
+   * @param views ViewRegistry containing OpenTelemetry views registered with this meter context.
+   */
   static std::unique_ptr<MeterContext> Create(std::unique_ptr<ViewRegistry> views);
 
+  /**
+   * Create a MeterContext with specified views and resource.
+   * @param views ViewRegistry containing OpenTelemetry views registered with this meter context.
+   * @param resource The OpenTelemetry resource associated with this meter context.
+   * @return A unique pointer to the created MeterContext object.
+   */
   static std::unique_ptr<MeterContext> Create(
       std::unique_ptr<ViewRegistry> views,
       const opentelemetry::sdk::resource::Resource &resource);
+
+  /**
+   * Create a MeterContext with specified views, resource and meter scope configurator.
+   * @param views ViewRegistry containing OpenTelemetry views registered with this meter context.
+   * @param resource The OpenTelemetry resource associated with this meter context.
+   * @param meter_configurator A scope configurator defining the behavior of a meter associated with
+   * this meter context.
+   * @return A unique pointer to the created MeterContext object.
+   */
+  static std::unique_ptr<MeterContext> Create(
+      std::unique_ptr<ViewRegistry> views,
+      const opentelemetry::sdk::resource::Resource &resource,
+      std::unique_ptr<instrumentationscope::ScopeConfigurator<MeterConfig>> meter_configurator);
 };
 
 }  // namespace metrics

sdk/include/opentelemetry/sdk/metrics/meter_provider.h

@@ -20,6 +20,9 @@
 #include "opentelemetry/sdk/resource/resource.h"
 #include "opentelemetry/version.h"
 
+#include "opentelemetry/sdk/instrumentationscope/scope_configurator.h"
+#include "opentelemetry/sdk/metrics/meter.h"
+
 #ifdef ENABLE_METRICS_EXEMPLAR_PREVIEW
 #  include "opentelemetry/sdk/metrics/exemplar/filter_type.h"
 #endif
@@ -34,13 +37,19 @@ class OPENTELEMETRY_EXPORT MeterProvider final : public opentelemetry::metrics::
 {
 public:
   /**
-   * Initialize a new meter provider
+   * Initialize a new meter provider.
    * @param views The views for this meter provider
    * @param resource  The resources for this meter provider.
+   * @param meter_configurator Provides access to a function that computes the MeterConfig for
+   * Meters provided by this MeterProvider.
    */
   MeterProvider(
       std::unique_ptr<ViewRegistry> views     = std::unique_ptr<ViewRegistry>(new ViewRegistry()),
-      const sdk::resource::Resource &resource = sdk::resource::Resource::Create({})) noexcept;
+      const sdk::resource::Resource &resource = sdk::resource::Resource::Create({}),
+      std::unique_ptr<instrumentationscope::ScopeConfigurator<MeterConfig>> meter_configurator =
+          std::make_unique<instrumentationscope::ScopeConfigurator<MeterConfig>>(
+              instrumentationscope::ScopeConfigurator<MeterConfig>::Builder(MeterConfig::Default())
+                  .Build())) noexcept;
 
   /**
    * Initialize a new meter provider with a specified context

sdk/include/opentelemetry/sdk/metrics/meter_provider_factory.h

@@ -30,6 +30,11 @@ class OPENTELEMETRY_EXPORT MeterProviderFactory
       std::unique_ptr<ViewRegistry> views,
       const opentelemetry::sdk::resource::Resource &resource);
 
+  static std::unique_ptr<opentelemetry::sdk::metrics::MeterProvider> Create(
+      std::unique_ptr<ViewRegistry> views,
+      const opentelemetry::sdk::resource::Resource &resource,
+      std::unique_ptr<instrumentationscope::ScopeConfigurator<MeterConfig>> meter_configurator);
+
   static std::unique_ptr<opentelemetry::sdk::metrics::MeterProvider> Create(
       std::unique_ptr<sdk::metrics::MeterContext> context);
 };

sdk/src/metrics/CMakeLists.txt

@@ -8,6 +8,7 @@ add_library(
   meter_provider.cc
   meter_provider_factory.cc
   meter.cc
+  meter_config.cc
   meter_context.cc
   meter_context_factory.cc
   metric_reader.cc