Add support for multiple readers

src/OpenTelemetry/.publicApi/net461/PublicAPI.Unshipped.txt

@@ -121,7 +121,7 @@ static OpenTelemetry.Metrics.MetricTypeExtensions.IsGauge(this OpenTelemetry.Met
 static OpenTelemetry.Metrics.MetricTypeExtensions.IsHistogram(this OpenTelemetry.Metrics.MetricType self) -> bool
 static OpenTelemetry.Metrics.MetricTypeExtensions.IsLong(this OpenTelemetry.Metrics.MetricType self) -> bool
 static OpenTelemetry.Metrics.MetricTypeExtensions.IsSum(this OpenTelemetry.Metrics.MetricType self) -> bool
-static OpenTelemetry.ProviderExtensions.GetMetricCollect(this OpenTelemetry.BaseProvider baseProvider) -> System.Func<OpenTelemetry.Batch<OpenTelemetry.Metrics.Metric>>
+static OpenTelemetry.ProviderExtensions.GetObservableInstrumentCollectCallback(this OpenTelemetry.BaseProvider baseProvider) -> System.Action
 static OpenTelemetry.Sdk.CreateMeterProviderBuilder() -> OpenTelemetry.Metrics.MeterProviderBuilder
 static readonly OpenTelemetry.Metrics.MetricStreamConfiguration.Drop -> OpenTelemetry.Metrics.MetricStreamConfiguration
 virtual OpenTelemetry.BaseExporter<T>.OnForceFlush(int timeoutMilliseconds) -> bool

src/OpenTelemetry/.publicApi/netstandard2.0/PublicAPI.Unshipped.txt

@@ -121,7 +121,7 @@ static OpenTelemetry.Metrics.MetricTypeExtensions.IsGauge(this OpenTelemetry.Met
 static OpenTelemetry.Metrics.MetricTypeExtensions.IsHistogram(this OpenTelemetry.Metrics.MetricType self) -> bool
 static OpenTelemetry.Metrics.MetricTypeExtensions.IsLong(this OpenTelemetry.Metrics.MetricType self) -> bool
 static OpenTelemetry.Metrics.MetricTypeExtensions.IsSum(this OpenTelemetry.Metrics.MetricType self) -> bool
-static OpenTelemetry.ProviderExtensions.GetMetricCollect(this OpenTelemetry.BaseProvider baseProvider) -> System.Func<OpenTelemetry.Batch<OpenTelemetry.Metrics.Metric>>
+static OpenTelemetry.ProviderExtensions.GetObservableInstrumentCollectCallback(this OpenTelemetry.BaseProvider baseProvider) -> System.Action
 static OpenTelemetry.Sdk.CreateMeterProviderBuilder() -> OpenTelemetry.Metrics.MeterProviderBuilder
 static readonly OpenTelemetry.Metrics.MetricStreamConfiguration.Drop -> OpenTelemetry.Metrics.MetricStreamConfiguration
 virtual OpenTelemetry.BaseExporter<T>.OnForceFlush(int timeoutMilliseconds) -> bool

src/OpenTelemetry/CHANGELOG.md

@@ -26,30 +26,33 @@
   ([#2542](https://github.com/open-telemetry/opentelemetry-dotnet/pull/2542))
 
 * Added wildcard support for AddMeter.
-([#2459](https://github.com/open-telemetry/opentelemetry-dotnet/pull/2459))
+  ([#2459](https://github.com/open-telemetry/opentelemetry-dotnet/pull/2459))
+
+* Add support for multiple Metric readers
+  ([#2596](https://github.com/open-telemetry/opentelemetry-dotnet/pull/2596))
 
 ## 1.2.0-beta1
 
 Released 2021-Oct-08
 
-* Exception from Observable instrument callbacks does not
-  result in entire metrics being lost.
+* Exception from Observable instrument callbacks does not result in entire
+  metrics being lost.
 
-* SDK is allocation-free on recording of measurements with
-  upto 8 tags.
+* SDK is allocation-free on recording of measurements with upto 8 tags.
 
 * TracerProviderBuilder.AddLegacySource now supports wildcard activity names.
   ([#2183](https://github.com/open-telemetry/opentelemetry-dotnet/issues/2183))
 
-* Instrument and View names are validated
-  [according with the spec](https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/api.md#instrument).
+* Instrument and View names are validated [according with the
+  spec](https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/api.md#instrument).
   ([#2470](https://github.com/open-telemetry/opentelemetry-dotnet/issues/2470))
 
 ## 1.2.0-alpha4
 
 Released 2021-Sep-23
 
-* `BatchExportProcessor.OnShutdown` will now log the count of dropped telemetry items.
+* `BatchExportProcessor.OnShutdown` will now log the count of dropped telemetry
+  items.
   ([#2331](https://github.com/open-telemetry/opentelemetry-dotnet/pull/2331))
 * Changed `CompositeProcessor<T>.OnForceFlush` to meet with the spec
   requirement. Now the SDK will invoke `ForceFlush` on all registered
@@ -60,36 +63,39 @@ Released 2021-Sep-23
 
 Released 2021-Sep-13
 
-* Metrics perf improvements, bug fixes.
-  Replace MetricProcessor with MetricReader.
+* Metrics perf improvements, bug fixes. Replace MetricProcessor with
+  MetricReader.
   ([#2306](https://github.com/open-telemetry/opentelemetry-dotnet/pull/2306))
 
-* Add `BatchExportActivityProcessorOptions` which supports field value overriding
-  using `OTEL_BSP_SCHEDULE_DELAY`, `OTEL_BSP_EXPORT_TIMEOUT`,
-  `OTEL_BSP_MAX_QUEUE_SIZE`, `OTEL_BSP_MAX_EXPORT_BATCH_SIZE`
-  envionmental variables as defined in the
+* Add `BatchExportActivityProcessorOptions` which supports field value
+  overriding using `OTEL_BSP_SCHEDULE_DELAY`, `OTEL_BSP_EXPORT_TIMEOUT`,
+  `OTEL_BSP_MAX_QUEUE_SIZE`, `OTEL_BSP_MAX_EXPORT_BATCH_SIZE` envionmental
+  variables as defined in the
   [specification](https://github.com/open-telemetry/opentelemetry-specification/blob/v1.5.0/specification/sdk-environment-variables.md#batch-span-processor).
   ([#2219](https://github.com/open-telemetry/opentelemetry-dotnet/pull/2219))
 
 ## 1.2.0-alpha2
 
 Released 2021-Aug-24
 
-* More Metrics features. All instrument types, push/pull
-  exporters, Delta/Cumulative temporality supported.
+* More Metrics features. All instrument types, push/pull exporters,
+  Delta/Cumulative temporality supported.
 
-* `ResourceBuilder.CreateDefault` has detectors for
-  `OTEL_RESOURCE_ATTRIBUTES`, `OTEL_SERVICE_NAME` environment variables
-  so that explicit `AddEnvironmentVariableDetector` call is not needed. ([#2247](https://github.com/open-telemetry/opentelemetry-dotnet/pull/2247))
+* `ResourceBuilder.CreateDefault` has detectors for `OTEL_RESOURCE_ATTRIBUTES`,
+  `OTEL_SERVICE_NAME` environment variables so that explicit
+  `AddEnvironmentVariableDetector` call is not needed.
+  ([#2247](https://github.com/open-telemetry/opentelemetry-dotnet/pull/2247))
 
 * `ResourceBuilder.AddEnvironmentVariableDetector` handles `OTEL_SERVICE_NAME`
-   environmental variable. ([#2209](https://github.com/open-telemetry/opentelemetry-dotnet/pull/2209))
+   environmental variable.
+   ([#2209](https://github.com/open-telemetry/opentelemetry-dotnet/pull/2209))
 
-* Removes upper constraint for Microsoft.Extensions.Logging
-  dependencies. ([#2179](https://github.com/open-telemetry/opentelemetry-dotnet/pull/2179))
+* Removes upper constraint for Microsoft.Extensions.Logging dependencies.
+  ([#2179](https://github.com/open-telemetry/opentelemetry-dotnet/pull/2179))
 
-* OpenTelemetryLogger modified to not throw, when the
-  formatter supplied in ILogger.Log call is null. ([#2200](https://github.com/open-telemetry/opentelemetry-dotnet/pull/2200))
+* OpenTelemetryLogger modified to not throw, when the formatter supplied in
+  ILogger.Log call is null.
+  ([#2200](https://github.com/open-telemetry/opentelemetry-dotnet/pull/2200))
 
 ## 1.2.0-alpha1
 
@@ -100,7 +106,8 @@ Released 2021-Jul-23
   ([#2174](https://github.com/open-telemetry/opentelemetry-dotnet/pull/2174))
 
 * Removes .NET Framework 4.5.2, .NET 4.6 support. The minimum .NET Framework
-  version supported is .NET 4.6.1. ([#2138](https://github.com/open-telemetry/opentelemetry-dotnet/issues/2138))
+  version supported is .NET 4.6.1.
+  ([#2138](https://github.com/open-telemetry/opentelemetry-dotnet/issues/2138))
 
 ## 1.1.0
 
@@ -137,8 +144,8 @@ Released 2021-May-11
 Released 2021-Apr-23
 
 * Use `AssemblyFileVersionAttribute` instead of `FileVersionInfo.GetVersionInfo`
-  to get the SDK version attribute to ensure that it works when the assembly
-  is not loaded directly from a file on disk
+  to get the SDK version attribute to ensure that it works when the assembly is
+  not loaded directly from a file on disk
   ([#1908](https://github.com/open-telemetry/opentelemetry-dotnet/issues/1908))
 
 ## 1.1.0-beta1

src/OpenTelemetry/Metrics/CompositeMetricReader.cs

@@ -22,11 +22,15 @@
 
 namespace OpenTelemetry.Metrics
 {
-    internal sealed class CompositeMetricReader : MetricReader
+    /// <summary>
+    /// CompositeMetricReader that does not deal with adding metrics and recording measurements.
+    /// </summary>
+    internal sealed partial class CompositeMetricReader : MetricReader
     {
         private readonly DoublyLinkedListNode head;
         private DoublyLinkedListNode tail;
         private bool disposed;
+        private int count;
 
         public CompositeMetricReader(IEnumerable<MetricReader> readers)
         {
@@ -40,6 +44,7 @@ public CompositeMetricReader(IEnumerable<MetricReader> readers)
 
             this.head = new DoublyLinkedListNode(iter.Current);
             this.tail = this.head;
+            this.count++;
 
             while (iter.MoveNext())
             {
@@ -57,6 +62,7 @@ public CompositeMetricReader AddReader(MetricReader reader)
             };
             this.tail.Next = node;
             this.tail = node;
+            this.count++;
 
             return this;
         }

src/OpenTelemetry/Metrics/CompositeMetricReaderExt.cs

@@ -0,0 +1,149 @@
+// <copyright file="CompositeMetricReaderExt.cs" company="OpenTelemetry Authors">
+// Copyright The 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.
+// </copyright>
+
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Diagnostics.Metrics;
+
+namespace OpenTelemetry.Metrics
+{
+    /// <summary>
+    /// CompositeMetricReader that deals with adding metrics and recording measurements.
+    /// </summary>
+    internal sealed partial class CompositeMetricReader
+    {
+        internal List<Metric> AddMetricsWithNoViews(Instrument instrument)
+        {
+            var metrics = new List<Metric>(this.count);
+            for (var cur = this.head; cur != null; cur = cur.Next)
+            {
+                var metric = cur.Value.AddMetricWithNoViews(instrument);
+                metrics.Add(metric);
+            }
+
+            return metrics;
+        }
+
+        internal void RecordSingleStreamLongMeasurements(List<Metric> metrics, long value, ReadOnlySpan<KeyValuePair<string, object>> tags)
+        {
+            Debug.Assert(metrics.Count == this.count, "The count of metrics to be updated for a CompositeReader must match the number of individual readers.");
+
+            int index = 0;
+            for (var cur = this.head; cur != null; cur = cur.Next)
+            {
+                if (metrics[index] != null)
+                {
+                    cur.Value.RecordSingleStreamLongMeasurement(metrics[index], value, tags);
+                }
+
+                index++;
+            }
+        }
+
+        internal void RecordSingleStreamDoubleMeasurements(List<Metric> metrics, double value, ReadOnlySpan<KeyValuePair<string, object>> tags)
+        {
+            Debug.Assert(metrics.Count == this.count, "The count of metrics to be updated for a CompositeReader must match the number of individual readers.");
+
+            int index = 0;
+            for (var cur = this.head; cur != null; cur = cur.Next)
+            {
+                if (metrics[index] != null)
+                {
+                    cur.Value.RecordSingleStreamDoubleMeasurement(metrics[index], value, tags);
+                }
+
+                index++;
+            }
+        }
+
+        internal List<List<Metric>> AddMetricsSuperListWithViews(Instrument instrument, List<MetricStreamConfiguration> metricStreamConfigs)
+        {
+            var metricsSuperList = new List<List<Metric>>(this.count);
+            for (var cur = this.head; cur != null; cur = cur.Next)
+            {
+                var metrics = cur.Value.AddMetricsListWithViews(instrument, metricStreamConfigs);
+                metricsSuperList.Add(metrics);
+            }
+
+            return metricsSuperList;
+        }
+
+        internal void RecordLongMeasurements(List<List<Metric>> metricsSuperList, long value, ReadOnlySpan<KeyValuePair<string, object>> tags)
+        {
+            Debug.Assert(metricsSuperList.Count == this.count, "The count of metrics to be updated for a CompositeReader must match the number of individual readers.");
+
+            int index = 0;
+            for (var cur = this.head; cur != null; cur = cur.Next)
+            {
+                if (metricsSuperList[index].Count > 0)
+                {
+                    cur.Value.RecordLongMeasurement(metricsSuperList[index], value, tags);
+                }
+
+                index++;
+            }
+        }
+
+        internal void RecordDoubleMeasurements(List<List<Metric>> metricsSuperList, double value, ReadOnlySpan<KeyValuePair<string, object>> tags)
+        {
+            Debug.Assert(metricsSuperList.Count == this.count, "The count of metrics to be updated for a CompositeReader must match the number of individual readers.");
+
+            int index = 0;
+            for (var cur = this.head; cur != null; cur = cur.Next)
+            {
+                if (metricsSuperList[index].Count > 0)
+                {
+                    cur.Value.RecordDoubleMeasurement(metricsSuperList[index], value, tags);
+                }
+
+                index++;
+            }
+        }
+
+        internal void CompleteSingleStreamMeasurements(List<Metric> metrics)
+        {
+            Debug.Assert(metrics.Count == this.count, "The count of metrics to be updated for a CompositeReader must match the number of individual readers.");
+
+            int index = 0;
+            for (var cur = this.head; cur != null; cur = cur.Next)
+            {
+                if (metrics[index] != null)
+                {
+                    cur.Value.CompleteSingleStreamMeasurement(metrics[index]);
+                }
+
+                index++;
+            }
+        }
+
+        internal void CompleteMesaurements(List<List<Metric>> metricsSuperList)
+        {
+            Debug.Assert(metricsSuperList.Count == this.count, "The count of metrics to be updated for a CompositeReader must match the number of individual readers.");
+
+            int index = 0;
+            for (var cur = this.head; cur != null; cur = cur.Next)
+            {
+                if (metricsSuperList[index].Count > 0)
+                {
+                    cur.Value.CompleteMeasurement(metricsSuperList[index]);
+                }
+
+                index++;
+            }
+        }
+    }
+}

src/OpenTelemetry/Metrics/MeterProviderBuilderBase.cs

@@ -71,11 +71,6 @@ public override MeterProviderBuilder AddMeter(params string[] names)
 
         internal MeterProviderBuilder AddReader(MetricReader reader)
         {
-            if (this.MetricReaders.Count >= 1)
-            {
-                throw new InvalidOperationException("Only one Metricreader is allowed.");
-            }
-
             this.MetricReaders.Add(reader);
             return this;
         }