Add a temp project with Metric API (which will come eventually from runtime)

OpenTelemetry.sln

@@ -207,6 +207,8 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "exception-reporting", "docs
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "customizing-the-sdk", "docs\trace\customizing-the-sdk\customizing-the-sdk.csproj", "{64E3D8BB-93AB-4571-93F7-ED8D64DFFD06}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "System.Diagnostics.Metrics.Temp", "src\System.Diagnostics.Metrics.Temp\System.Diagnostics.Metrics.Temp.csproj", "{4481390E-52F5-46A6-8510-3B1433ABAFE6}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -405,6 +407,10 @@ Global
 		{64E3D8BB-93AB-4571-93F7-ED8D64DFFD06}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{64E3D8BB-93AB-4571-93F7-ED8D64DFFD06}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{64E3D8BB-93AB-4571-93F7-ED8D64DFFD06}.Release|Any CPU.Build.0 = Release|Any CPU
+		{4481390E-52F5-46A6-8510-3B1433ABAFE6}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{4481390E-52F5-46A6-8510-3B1433ABAFE6}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{4481390E-52F5-46A6-8510-3B1433ABAFE6}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{4481390E-52F5-46A6-8510-3B1433ABAFE6}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

src/OpenTelemetry.Api/Metrics/MeterProviderBuilder.cs

@@ -0,0 +1,39 @@
+// <copyright file="MeterProviderBuilder.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;
+
+namespace OpenTelemetry.Metrics
+{
+    /// <summary>
+    /// MeterProviderBuilder base class.
+    /// </summary>
+    public abstract class MeterProviderBuilder
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="MeterProviderBuilder"/> class.
+        /// </summary>
+        protected MeterProviderBuilder()
+        {
+        }
+
+        /// <summary>
+        /// Adds given meter source names to the list of subscribed sources.
+        /// </summary>
+        /// <param name="names">Meter source names.</param>
+        /// <returns>Returns <see cref="MeterProviderBuilder"/> for chaining.</returns>
+        public abstract MeterProviderBuilder AddSource(params string[] names);
+    }
+}

src/OpenTelemetry/Metrics/MeterProviderBuilderSdk.cs

@@ -0,0 +1,30 @@
+// <copyright file="MeterProviderBuilderSdk.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>
+
+namespace OpenTelemetry.Metrics
+{
+    public class MeterProviderBuilderSdk : MeterProviderBuilder
+    {
+        protected MeterProviderBuilderSdk()
+        {
+        }
+
+        public override MeterProviderBuilder AddSource(params string[] names)
+        {
+            return this;
+        }
+    }
+}

src/OpenTelemetry/OpenTelemetry.csproj

@@ -26,6 +26,7 @@
 
   <ItemGroup>
     <ProjectReference Include="$(RepoRoot)\src\OpenTelemetry.Api\OpenTelemetry.Api.csproj" />
+    <ProjectReference Include="$(RepoRoot)\src\System.Diagnostics.Metrics.Temp\System.Diagnostics.Metrics.Temp.csproj" />
   </ItemGroup>
 
   <ItemGroup>

src/System.Diagnostics.Metrics.Temp/Counter.cs

@@ -0,0 +1,42 @@
+// <copyright file="ActivityExtensions.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>
+
+#nullable enable
+
+namespace System.Diagnostics.Metrics
+{
+    public class Counter<T> : MeterInstrument<T>
+        where T : unmanaged
+    {
+        internal Counter(Meter meter, string name, string? description, string? unit) :
+            base(meter, name, description, unit)
+        {
+            Publish();
+        }
+
+        public void Add(T measurement) => RecordMeasurement(measurement);
+        public void Add(T measurement,
+            (string LabelName, object LabelValue) label1) => RecordMeasurement(measurement, label1);
+        public void Add(T measurement,
+            (string LabelName, object LabelValue) label1,
+            (string LabelName, object LabelValue) label2) => RecordMeasurement(measurement, label1, label2);
+        public void Add(T measurement,
+            (string LabelName, object LabelValue) label1,
+            (string LabelName, object LabelValue) label2,
+            (string LabelName, object LabelValue) label3) => RecordMeasurement(measurement, label1, label2, label3);
+        public void Add(T measurement, params (string LabelName, object LabelValue)[] labels) => RecordMeasurement(measurement, labels);
+    }
+}

src/System.Diagnostics.Metrics.Temp/CounterFunc.cs

@@ -0,0 +1,43 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+#nullable enable
+
+namespace System.Diagnostics.Metrics
+{
+    public class CounterFunc<T> : ObservableMeterInstrument<T> where T : unmanaged
+    {
+        // This is either a Func<T> or an Func<IEnumerable<Measurement<T>>>
+        object _observeValueFunc;
+
+        public CounterFunc(Meter meter, string name, Func<T> observeValue, string? description, string? unit) :
+            base(meter, name, description, unit)
+        {
+            _observeValueFunc = observeValue;
+            Publish();
+        }
+
+        public CounterFunc(Meter meter, string name, Func<IEnumerable<Measurement<T>>> observeValues, string? description, string? unit) :
+            base(meter, name, description, unit)
+        {
+            _observeValueFunc = observeValues;
+            Publish();
+        }
+
+        protected override IEnumerable<Measurement<T>> Observe()
+        {
+            if (_observeValueFunc is Func<T>)
+            {
+                T value = ((Func<T>)_observeValueFunc)();
+                return new Measurement<T>[] { new Measurement<T>(value) };
+            }
+            else
+            {
+                return ((Func<IEnumerable<Measurement<T>>>)_observeValueFunc)();
+            }
+        }
+    }
+}

src/System.Diagnostics.Metrics.Temp/Distribution.cs

@@ -0,0 +1,29 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace System.Diagnostics.Metrics
+{
+    public class Distribution<T> : MeterInstrument<T> where T : unmanaged
+    {
+        internal Distribution(Meter meter, string name, string? description, string? unit)
+            : base(meter, name, description, unit)
+        {
+            Publish();
+        }
+
+        public void Record(T measurement) => RecordMeasurement(measurement);
+        public void Record(T measurement,
+            (string LabelName, object LabelValue) label1) => RecordMeasurement(measurement, label1);
+        public void Record(T measurement,
+            (string LabelName, object LabelValue) label1,
+            (string LabelName, object LabelValue) label2) => RecordMeasurement(measurement, label1, label2);
+        public void Record(T measurement,
+            (string LabelName, object LabelValue) label1,
+            (string LabelName, object LabelValue) label2,
+            (string LabelName, object LabelValue) label3) => RecordMeasurement(measurement, label1, label2, label3);
+        public void Record(T measurement, params (string LabelName, object LabelValue)[] labels) => RecordMeasurement(measurement, labels);
+    }
+}

src/System.Diagnostics.Metrics.Temp/Gauge.cs

@@ -0,0 +1,29 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+#nullable enable
+
+namespace System.Diagnostics.Metrics
+{
+    public class Gauge<T> : MeterInstrument<T> where T : unmanaged
+    {
+        internal Gauge(Meter meter, string name, string? description, string? unit) :
+            base(meter, name, description, unit)
+        {
+            Publish();
+        }
+
+        public void Set(T val)
+        {
+            RecordMeasurement(val);
+        }
+
+        public void Set(T val, params (string LabelName, object LabelValue)[] labels)
+        {
+            RecordMeasurement(val, labels);
+        }
+    }
+}

src/System.Diagnostics.Metrics.Temp/Meter.cs

@@ -0,0 +1,84 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+#nullable enable
+
+namespace System.Diagnostics.Metrics
+{
+    public class Meter : IDisposable
+    {
+        List<MeterInstrument>? _instruments = new List<MeterInstrument>();
+
+        public Meter(string name) : this(name, "") { }
+
+        public Meter(string name, string version)
+        {
+            Name = name;
+            Version = version;
+            lock (MeterInstrumentCollection.Lock)
+            {
+                MeterInstrumentCollection.Instance.AddMeter(this);
+            }
+        }
+
+        public Counter<T> CreateCounter<T>(string name, string? description = null, string? unit = null) where T : unmanaged
+        {
+            return new Counter<T>(this, name, description, unit);
+        }
+
+        public CounterFunc<T> CreateCounterFunc<T>(string name, Func<T> observeValue, string? description = null, string? unit = null) where T : unmanaged
+        {
+            return new CounterFunc<T>(this, name, observeValue, description, unit);
+        }
+
+        public CounterFunc<T> CreateCounterFunc<T>(string name, Func<IEnumerable<Measurement<T>>> observeValues, string? description = null, string? unit = null) where T : unmanaged
+        {
+            return new CounterFunc<T>(this, name, observeValues, description, unit);
+        }
+
+        public Gauge<T> CreateGauge<T>(string name, string? description = null, string? unit = null) where T : unmanaged
+        {
+            return new Gauge<T>(this, name, description, unit);
+        }
+
+        public Distribution<T> CreateDistribution<T>(string name, string? description = null, string? unit = null) where T : unmanaged
+        {
+            return new Distribution<T>(this, name, description, unit);
+        }
+
+        public string Name { get; }
+        public string Version { get; }
+
+
+        internal void PublishInstrument(MeterInstrument instrument)
+        {
+            lock (MeterInstrumentCollection.Lock)
+            {
+                if (_instruments != null) // if not disposed
+                {
+                    _instruments.Add(instrument);
+                    MeterInstrumentCollection.Instance.PublishInstrument(instrument);
+                }
+            }
+        }
+
+        public void Dispose()
+        {
+            lock (MeterInstrumentCollection.Lock)
+            {
+                MeterInstrumentCollection.Instance.RemoveMeter(this);
+                _instruments = null;
+            }
+        }
+
+        internal IEnumerable<MeterInstrument> Instruments =>
+#if NET452
+                (IEnumerable<MeterInstrument>?)_instruments ?? new MeterInstrument[0];
+#else
+                (IEnumerable<MeterInstrument>?)_instruments ?? Array.Empty<MeterInstrument>();
+#endif
+    }
+}