Add a very basic prometheus exporter

OpenTelemetry.sln

@@ -208,7 +208,9 @@ 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}") = "getting-started", "docs\metrics\getting-started\getting-started.csproj", "{DFB0AD2F-11BE-4BCD-A77B-1018C3344FA8}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "getting-started", "docs\metrics\getting-started\getting-started.csproj", "{DFB0AD2F-11BE-4BCD-A77B-1018C3344FA8}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "OpenTelemetry.Exporter.Prometheus", "src\OpenTelemetry.Exporter.Prometheus\OpenTelemetry.Exporter.Prometheus.csproj", "{52158A12-E7EF-45A1-859F-06F9B17410CB}"
 EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
@@ -412,6 +414,10 @@ Global
 		{DFB0AD2F-11BE-4BCD-A77B-1018C3344FA8}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{DFB0AD2F-11BE-4BCD-A77B-1018C3344FA8}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{DFB0AD2F-11BE-4BCD-A77B-1018C3344FA8}.Release|Any CPU.Build.0 = Release|Any CPU
+		{52158A12-E7EF-45A1-859F-06F9B17410CB}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{52158A12-E7EF-45A1-859F-06F9B17410CB}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{52158A12-E7EF-45A1-859F-06F9B17410CB}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{52158A12-E7EF-45A1-859F-06F9B17410CB}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

examples/Console/Examples.Console.csproj

@@ -36,5 +36,6 @@
     <ProjectReference Include="$(RepoRoot)\src\OpenTelemetry.Exporter.Zipkin\OpenTelemetry.Exporter.Zipkin.csproj" />
     <ProjectReference Include="$(RepoRoot)\src\OpenTelemetry.Exporter.Jaeger\OpenTelemetry.Exporter.Jaeger.csproj" />
     <ProjectReference Include="$(RepoRoot)\src\OpenTelemetry.Exporter.InMemory\OpenTelemetry.Exporter.InMemory.csproj" />
+    <ProjectReference Include="$(RepoRoot)\src\OpenTelemetry.Exporter.Prometheus\OpenTelemetry.Exporter.Prometheus.csproj" />
   </ItemGroup>
 </Project>

examples/Console/Program.cs

@@ -46,7 +46,7 @@ public static void Main(string[] args)
                 .MapResult(
                     (JaegerOptions options) => TestJaegerExporter.Run(options.Host, options.Port),
                     (ZipkinOptions options) => TestZipkinExporter.Run(options.Uri),
-                    (PrometheusOptions options) => TestPrometheusExporter.Run(options.Port, options.PushIntervalInSecs, options.DurationInMins),
+                    (PrometheusOptions options) => TestPrometheusExporter.Run(options.Port, options.DurationInMins),
                     (MetricsOptions options) => TestMetrics.Run(options),
                     (GrpcNetClientOptions options) => TestGrpcNetClient.Run(),
                     (HttpClientOptions options) => TestHttpClient.Run(),
@@ -83,13 +83,10 @@ internal class ZipkinOptions
     [Verb("prometheus", HelpText = "Specify the options required to test Prometheus")]
     internal class PrometheusOptions
     {
-        [Option('i', "pushIntervalInSecs", Default = 15, HelpText = "The interval at which Push controller pushes metrics.", Required = false)]
-        public int PushIntervalInSecs { get; set; }
-
         [Option('p', "port", Default = 9184, HelpText = "The port to expose metrics. The endpoint will be http://localhost:port/metrics (This is the port from which your Prometheus server scraps metrics from.)", Required = false)]
         public int Port { get; set; }
 
-        [Option('d', "duration", Default = 2, HelpText = "Total duration in minutes to run the demo. Run atleast for a min to see metrics flowing.", Required = false)]
+        [Option('d', "duration", Default = 2, HelpText = "Total duration in minutes to run the demo.", Required = false)]
         public int DurationInMins { get; set; }
     }
 

examples/Console/TestPrometheusExporter.cs

@@ -17,18 +17,22 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.Metrics;
+using System.Threading;
 using System.Threading.Tasks;
 using OpenTelemetry;
+using OpenTelemetry.Metrics;
 using OpenTelemetry.Trace;
 
 namespace Examples.Console
 {
     internal class TestPrometheusExporter
     {
-        internal static object Run(int port, int pushIntervalInSecs, int totalDurationInMins)
-        {
-            System.Console.WriteLine($"OpenTelemetry Prometheus Exporter is making metrics available at http://localhost:{port}/metrics/");
+        private static readonly Meter MyMeter = new Meter("TestMeter", "0.0.1");
+        private static readonly Counter<long> Counter = MyMeter.CreateCounter<long>("counter");
 
+        internal static object Run(int port, int totalDurationInMins)
+        {
             /*
             Following is sample prometheus.yml config. Adjust port,interval as needed.
 
@@ -42,9 +46,37 @@ internal static object Run(int port, int pushIntervalInSecs, int totalDurationIn
                 static_configs:
                 - targets: ['localhost:9184']
             */
-            System.Console.WriteLine("Press Enter key to exit.");
-            System.Console.ReadLine();
+            using var meterProvider = Sdk.CreateMeterProviderBuilder()
+                .AddSource("TestMeter")
+                .AddPrometheusExporter(opt => opt.Url = $"http://localhost:{port}/metrics/")
+                .Build();
+
+            using var token = new CancellationTokenSource();
+            Task writeMetricTask = new Task(() =>
+            {
+                while (!token.IsCancellationRequested)
+                {
+                    Counter.Add(
+                                10,
+                                new KeyValuePair<string, object>("tag1", "value1"),
+                                new KeyValuePair<string, object>("tag2", "value2"));
 
+                    Counter.Add(
+                                100,
+                                new KeyValuePair<string, object>("tag1", "anothervalue"),
+                                new KeyValuePair<string, object>("tag2", "somethingelse"));
+                    Task.Delay(10).Wait();
+                }
+            });
+            writeMetricTask.Start();
+
+            token.CancelAfter(totalDurationInMins * 60 * 1000);
+
+            System.Console.WriteLine($"OpenTelemetry Prometheus Exporter is making metrics available at http://localhost:{port}/metrics/");
+            System.Console.WriteLine($"Press Enter key to exit now or will exit automatically after {totalDurationInMins} minutes.");
+            System.Console.ReadLine();
+            token.Cancel();
+            System.Console.WriteLine("Exiting...");
             return null;
         }
     }

src/OpenTelemetry.Exporter.Prometheus/Implementation/PrometheusExporterEventSource.cs

@@ -0,0 +1,76 @@
+// <copyright file="PrometheusExporterEventSource.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.Diagnostics.Tracing;
+using OpenTelemetry.Internal;
+
+namespace OpenTelemetry.Exporter.Prometheus.Implementation
+{
+    /// <summary>
+    /// EventSource events emitted from the project.
+    /// </summary>
+    [EventSource(Name = "OpenTelemetry-Exporter-Prometheus")]
+    internal class PrometheusExporterEventSource : EventSource
+    {
+        public static PrometheusExporterEventSource Log = new PrometheusExporterEventSource();
+
+        [NonEvent]
+        public void FailedExport(Exception ex)
+        {
+            if (this.IsEnabled(EventLevel.Error, (EventKeywords)(-1)))
+            {
+                this.FailedExport(ex.ToInvariantString());
+            }
+        }
+
+        [NonEvent]
+        public void FailedShutdown(Exception ex)
+        {
+            if (this.IsEnabled(EventLevel.Error, (EventKeywords)(-1)))
+            {
+                this.FailedShutdown(ex.ToInvariantString());
+            }
+        }
+
+        [NonEvent]
+        public void CanceledExport(Exception ex)
+        {
+            if (this.IsEnabled(EventLevel.Error, (EventKeywords)(-1)))
+            {
+                this.CanceledExport(ex.ToInvariantString());
+            }
+        }
+
+        [Event(1, Message = "Failed to export metrics: '{0}'", Level = EventLevel.Error)]
+        public void FailedExport(string exception)
+        {
+            this.WriteEvent(1, exception);
+        }
+
+        [Event(2, Message = "Canceled to export metrics: '{0}'", Level = EventLevel.Error)]
+        public void CanceledExport(string exception)
+        {
+            this.WriteEvent(2, exception);
+        }
+
+        [Event(3, Message = "Failed to shutdown Metrics server '{0}'", Level = EventLevel.Error)]
+        public void FailedShutdown(string exception)
+        {
+            this.WriteEvent(3, exception);
+        }
+    }
+}