O11Y-2256 : Resource can be passed into MeterProvider

lib/src/api/metrics/noop/noop_meter_provider.dart

@@ -1,5 +1,4 @@
 import 'package:opentelemetry/api.dart';
-import 'package:opentelemetry/src/api/metrics/noop/noop_meter.dart';
 import 'package:opentelemetry/src/experimental_api.dart';
 
 /// A noop registry for creating named [Meter]s.

lib/src/experimental_api.dart

@@ -1,3 +1,4 @@
 export 'api/metrics/counter.dart' show Counter;
 export 'api/metrics/meter_provider.dart' show MeterProvider;
 export 'api/metrics/meter.dart' show Meter;
+export 'api/metrics/noop/noop_meter.dart' show NoopMeter;

lib/src/experimental_sdk.dart

@@ -1,3 +1,7 @@
 export 'sdk/metrics/counter.dart' show Counter;
 export 'sdk/metrics/meter_provider.dart' show MeterProvider;
 export 'sdk/metrics/meter.dart' show Meter;
+export 'sdk/metrics/state/meter_shared_state.dart' show MeterSharedState;
+export 'sdk/metrics/state/meter_provider_shared_state.dart'
+    show MeterProviderSharedState;
+export 'sdk/resource/resource.dart' show Resource;

lib/src/sdk/common/instrumentation_scope.dart

@@ -0,0 +1,27 @@
+import 'package:opentelemetry/api.dart' as api;
+
+class InstrumentationScope {
+  final String _name;
+  final String _version;
+  final String _schemaUrl;
+  final List<api.Attribute> _attributes;
+
+  InstrumentationScope(
+      this._name, this._version, this._schemaUrl, this._attributes);
+
+  String get name {
+    return _name;
+  }
+
+  String get version {
+    return _version;
+  }
+
+  String get schemaUrl {
+    return _schemaUrl;
+  }
+
+  List<api.Attribute> get attributes {
+    return _attributes;
+  }
+}

lib/src/sdk/metrics/meter.dart

@@ -2,6 +2,11 @@ import 'package:opentelemetry/src/experimental_sdk.dart' as sdk;
 import 'package:opentelemetry/src/experimental_api.dart' as api;
 
 class Meter implements api.Meter {
+  // ignore: unused_field
+  final sdk.MeterSharedState _state;
+
+  Meter(this._state);
+
   @override
   api.Counter<T> createCounter<T extends num>(String name,
       {String description, String unit}) {

lib/src/sdk/metrics/meter_provider.dart

@@ -2,28 +2,39 @@ import 'package:opentelemetry/api.dart' as api;
 import 'package:opentelemetry/src/experimental_api.dart' as api;
 import 'package:opentelemetry/src/experimental_sdk.dart' as sdk;
 import 'package:logging/logging.dart';
-import 'package:opentelemetry/src/api/metrics/meter_key.dart';
+import 'package:opentelemetry/src/sdk/common/instrumentation_scope.dart';
+import 'package:opentelemetry/src/sdk/metrics/state/meter_provider_shared_state.dart';
 
 const invalidMeterNameMessage = 'Invalid Meter Name';
 
 class MeterProvider implements api.MeterProvider {
-  final _meters = <MeterKey, api.Meter>{};
   final _logger = Logger('opentelemetry.sdk.metrics.meterprovider');
+  final _shutdown = false;
+  final MeterProviderSharedState _sharedState;
+
+  sdk.Resource get resource => _sharedState.resource;
+
+  MeterProvider({sdk.Resource resource})
+      : _sharedState = MeterProviderSharedState(resource);
 
   @override
-  sdk.Meter get(String name,
+  api.Meter get(String name,
       {String version = '',
       String schemaUrl = '',
       List<api.Attribute> attributes = const []}) {
     if (name == null || name == '') {
       name = '';
       _logger.warning(invalidMeterNameMessage, '', StackTrace.current);
     }
-    version ??= '';
-    schemaUrl ??= '';
-    attributes ??= const [];
-    final key = MeterKey(name, version, schemaUrl, attributes);
 
-    return _meters.putIfAbsent(key, () => sdk.Meter());
+    if (_shutdown) {
+      _logger.warning('A shutdown MeterProvider cannot provide a Meter', '',
+          StackTrace.current);
+      return api.NoopMeter();
+    }
+
+    return _sharedState
+        .getMeterSharedState(InstrumentationScope(name, version, schemaUrl, attributes))
+        .meter;
   }
 }

lib/src/sdk/metrics/state/meter_provider_shared_state.dart

@@ -0,0 +1,27 @@
+import 'package:opentelemetry/sdk.dart';
+import 'package:opentelemetry/src/sdk/common/instrumentation_scope.dart';
+import 'package:opentelemetry/src/sdk/metrics/state/meter_shared_state.dart';
+import 'package:quiver/core.dart';
+
+int instrumentationScopeId(InstrumentationScope instrumentationScope) {
+  return hash4(instrumentationScope.name, instrumentationScope.version,
+      instrumentationScope.schemaUrl, instrumentationScope.attributes);
+}
+
+class MeterProviderSharedState {
+  Resource resource;
+  Map<int, MeterSharedState> meterSharedStates = {};
+
+  MeterProviderSharedState(this.resource);
+
+  MeterSharedState getMeterSharedState(
+      InstrumentationScope instrumentationScope) {
+    final id = instrumentationScopeId(instrumentationScope);
+    var meterSharedState = meterSharedStates[id];
+    if (meterSharedState == null) {
+      meterSharedState = MeterSharedState(this, instrumentationScope);
+      meterSharedStates[id] = meterSharedState;
+    }
+    return meterSharedState;
+  }
+}

lib/src/sdk/metrics/state/meter_shared_state.dart

@@ -0,0 +1,15 @@
+import 'package:opentelemetry/src/sdk/common/instrumentation_scope.dart';
+
+import 'package:opentelemetry/src/experimental_sdk.dart' as sdk;
+
+class MeterSharedState {
+  // ignore: unused_field
+  final sdk.MeterProviderSharedState _meterProviderSharedState;
+  // ignore: unused_field
+  final InstrumentationScope _instrumentationScope;
+  sdk.Meter meter;
+
+  MeterSharedState(this._meterProviderSharedState, this._instrumentationScope) {
+    meter = sdk.Meter(this);
+  }
+}

test/unit/sdk/metrics/meter_provider_test.dart

@@ -157,6 +157,12 @@ void main() {
       expect(identical(meterA, meterB), false);
     });
 
+    test('resource can be set', () {
+      final resource = sdk.Resource([api.Attribute.fromString('foo', 'bar')]);
+      final provider = sdk.MeterProvider(resource: resource);
+      expect(identical(resource, provider.resource), true);
+    });
+
     // todo: implement test that verifies that changes to attributes apply to
     // previously created meters
     // https://github.com/Workiva/opentelemetry-dart/issues/74