wip: used to review approach

src/OpenTelemetry.Adapter.Dependencies/DependenciesAdapter.cs

@@ -29,23 +29,23 @@ public class DependenciesAdapter : IDisposable
         /// <summary>
         /// Initializes a new instance of the <see cref="DependenciesAdapter"/> class.
         /// </summary>
-        /// <param name="tracerFactory">Tracer factory to get a tracer from.</param>
+        /// <param name="tracerProvider">Tracer provider to get a tracer from.</param>
         /// <param name="httpOptions">Http configuration options.</param>
         /// <param name="sqlOptions">Sql configuration options.</param>
-        public DependenciesAdapter(TracerFactoryBase tracerFactory, HttpClientAdapterOptions httpOptions = null, SqlClientAdapterOptions sqlOptions = null)
+        public DependenciesAdapter(ITracerProvider tracerProvider, HttpClientAdapterOptions httpOptions = null, SqlClientAdapterOptions sqlOptions = null)
         {
-            if (tracerFactory == null)
+            if (tracerProvider == null)
             {
-                throw new ArgumentNullException(nameof(tracerFactory));
+                throw new ArgumentNullException(nameof(tracerProvider));
             }
 
             var assemblyVersion = typeof(DependenciesAdapter).Assembly.GetName().Version;
 
-            var httpClientListener = new HttpClientAdapter(tracerFactory.GetTracer(nameof(HttpClientAdapter), "semver:" + assemblyVersion), httpOptions ?? new HttpClientAdapterOptions());
-            var httpWebRequestAdapter = new HttpWebRequestAdapter(tracerFactory.GetTracer(nameof(HttpWebRequestAdapter), "semver:" + assemblyVersion), httpOptions ?? new HttpClientAdapterOptions());
-            var azureClientsListener = new AzureClientsAdapter(tracerFactory.GetTracer(nameof(AzureClientsAdapter), "semver:" + assemblyVersion));
-            var azurePipelineListener = new AzurePipelineAdapter(tracerFactory.GetTracer(nameof(AzurePipelineAdapter), "semver:" + assemblyVersion));
-            var sqlClientListener = new SqlClientAdapter(tracerFactory.GetTracer(nameof(AzurePipelineAdapter), "semver:" + assemblyVersion), sqlOptions ?? new SqlClientAdapterOptions());
+            var httpClientListener = new HttpClientAdapter(tracerProvider.GetTracer(nameof(HttpClientAdapter), "semver:" + assemblyVersion), httpOptions ?? new HttpClientAdapterOptions());
+            var httpWebRequestAdapter = new HttpWebRequestAdapter(tracerProvider.GetTracer(nameof(HttpWebRequestAdapter), "semver:" + assemblyVersion), httpOptions ?? new HttpClientAdapterOptions());
+            var azureClientsListener = new AzureClientsAdapter(tracerProvider.GetTracer(nameof(AzureClientsAdapter), "semver:" + assemblyVersion));
+            var azurePipelineListener = new AzurePipelineAdapter(tracerProvider.GetTracer(nameof(AzurePipelineAdapter), "semver:" + assemblyVersion));
+            var sqlClientListener = new SqlClientAdapter(tracerProvider.GetTracer(nameof(AzurePipelineAdapter), "semver:" + assemblyVersion), sqlOptions ?? new SqlClientAdapterOptions());
 
             this.adapters.Add(httpClientListener);
             this.adapters.Add(httpWebRequestAdapter);

src/OpenTelemetry.Adapter.StackExchangeRedis/StackExchangeRedisCallsAdapter.cs

@@ -51,7 +51,7 @@ public StackExchangeRedisCallsAdapter(Tracer tracer)
 
             this.cancellationTokenSource = new CancellationTokenSource();
             this.cancellationToken = this.cancellationTokenSource.Token;
-            var spanType = typeof(TracerFactory).Assembly.GetType("OpenTelemetry.Trace.SpanSdk");
+            var spanType = typeof(TracerProviderSdk).Assembly.GetType("OpenTelemetry.Trace.SpanSdk");
 
             this.spanEndTimestampInfo = spanType?.GetProperty("EndTimestamp");
             if (this.spanEndTimestampInfo == null)

src/OpenTelemetry.Api/Trace/ITracerProvider.cs

@@ -0,0 +1,32 @@
+// <copyright file="ITracerProvider.cs" company="OpenTelemetry Authors">
+// Copyright 2018, 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.Trace
+{
+    /// <summary>
+    /// Creates Tracers for an instrumentation library.
+    /// </summary>
+    public interface ITracerProvider
+    {
+        /// <summary>
+        /// Returns an Tracer for a given name and version.
+        /// </summary>
+        /// <param name="name">Name of the instrumentation library.</param>
+        /// <param name="version">Version of the instrumentation library (optional).</param>
+        /// <returns>Tracer for the given name and version information.</returns>
+        Tracer GetTracer(string name, string version = null);
+    }
+}

src/OpenTelemetry.Api/Internal/BlankSpan.cs → src/OpenTelemetry.Api/Trace/NoopSpan.cs

@@ -1,4 +1,4 @@
-// <copyright file="BlankSpan.cs" company="OpenTelemetry Authors">
+// <copyright file="NoopSpan.cs" company="OpenTelemetry Authors">
 // Copyright 2018, OpenTelemetry Authors
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
@@ -18,19 +18,10 @@
 namespace OpenTelemetry.Trace
 {
     /// <summary>
-    /// Blank span.
+    /// No-op span.
     /// </summary>
-    internal sealed class BlankSpan : TelemetrySpan
+    public sealed class NoopSpan : TelemetrySpan
     {
-        /// <summary>
-        /// Blank span instance.
-        /// </summary>
-        public static readonly BlankSpan Instance = new BlankSpan();
-
-        private BlankSpan()
-        {
-        }
-
         /// <inheritdoc />
         public override SpanContext Context => default;
 

src/OpenTelemetry.Api/Trace/ProxyTracer.cs → src/OpenTelemetry.Api/Trace/NoopTracer.cs

@@ -1,4 +1,4 @@
-// <copyright file="ProxyTracer.cs" company="OpenTelemetry Authors">
+// <copyright file="NoopTracer.cs" company="OpenTelemetry Authors">
 // Copyright 2018, OpenTelemetry Authors
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
@@ -17,58 +17,49 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
-using System.Threading;
-using OpenTelemetry.Context.Propagation;
 
 namespace OpenTelemetry.Trace
 {
     /// <summary>
     /// No-op tracer.
     /// </summary>
-    internal sealed class ProxyTracer : Tracer
+    public sealed class NoopTracer : Tracer
     {
         private static readonly IDisposable NoopScope = new NoopDisposable();
 
-        private Tracer realTracer;
+        private readonly TelemetrySpan noopSpan = new NoopSpan();
 
         /// <inheritdoc/>
-        public override TelemetrySpan CurrentSpan => this.realTracer?.CurrentSpan ?? BlankSpan.Instance;
+        public override TelemetrySpan CurrentSpan => this.noopSpan;
 
         /// <inheritdoc/>
         public override IDisposable WithSpan(TelemetrySpan span, bool endOnDispose)
         {
-            return this.realTracer != null ? this.realTracer.WithSpan(span, endOnDispose) : NoopScope;
+            return NoopScope;
         }
 
+        /// <inheritdoc/>
         public override TelemetrySpan StartRootSpan(string operationName, SpanKind kind, SpanCreationOptions options)
         {
-            return this.realTracer != null ? this.realTracer.StartRootSpan(operationName, kind, options) : BlankSpan.Instance;
+            return this.noopSpan;
         }
 
+        /// <inheritdoc/>
         public override TelemetrySpan StartSpan(string operationName, TelemetrySpan parent, SpanKind kind, SpanCreationOptions options)
         {
-            return this.realTracer != null ? this.realTracer.StartSpan(operationName, parent, kind, options) : BlankSpan.Instance;
+            return this.noopSpan;
         }
 
+        /// <inheritdoc/>
         public override TelemetrySpan StartSpan(string operationName, in SpanContext parent, SpanKind kind, SpanCreationOptions options)
         {
-            return this.realTracer != null ? this.realTracer.StartSpan(operationName, parent, kind, options) : BlankSpan.Instance;
+            return this.noopSpan;
         }
 
+        /// <inheritdoc/>
         public override TelemetrySpan StartSpanFromActivity(string operationName, Activity activity, SpanKind kind, IEnumerable<Link> links)
         {
-            return this.realTracer != null ? this.realTracer.StartSpanFromActivity(operationName, activity, kind, links) : BlankSpan.Instance;
-        }
-
-        public void UpdateTracer(Tracer realTracer)
-        {
-            if (this.realTracer != null)
-            {
-                return;
-            }
-
-            // just in case user calls init concurrently
-            Interlocked.CompareExchange(ref this.realTracer, realTracer, null);
+            return this.noopSpan;
         }
 
         private class NoopDisposable : IDisposable

src/OpenTelemetry.Api/Trace/NoopTracerProvider.cs

@@ -0,0 +1,33 @@
+// <copyright file="NoopTracerProvider.cs" company="OpenTelemetry Authors">
+// Copyright 2018, 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.Trace
+{
+    /// <summary>
+    /// No-op tracer provider.
+    /// </summary>
+    public class NoopTracerProvider : ITracerProvider
+    {
+        private readonly NoopTracer tracer = new NoopTracer();
+
+        /// <inheritdoc/>
+        public Tracer GetTracer(string name, string version = null)
+        {
+            return this.tracer;
+        }
+    }
+}

src/OpenTelemetry.Api/Trace/TracerProvider.cs

@@ -0,0 +1,46 @@
+// <copyright file="TracerProvider.cs" company="OpenTelemetry Authors">
+// Copyright 2018, 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.Trace
+{
+    /// <summary>
+    /// Creates Tracers for an instrumentation library.
+    /// </summary>
+    public class TracerProvider
+    {
+        /// <summary>
+        /// Gets or sets the global instance of <see cref="ITracerProvider"/>.
+        /// </summary>
+        public static ITracerProvider GlobalInstance { get; protected set; } = new NoopTracerProvider();
+
+        /// <summary>
+        /// Returns an Tracer for a given name and version.
+        /// </summary>
+        /// <param name="name">Name of the instrumentation library.</param>
+        /// <param name="version">Version of the instrumentation library (optional).</param>
+        /// <returns>Tracer for the given name and version information.</returns>
+        public static Tracer GetTracer(string name, string version = null)
+        {
+            return GlobalInstance.GetTracer(name, version);
+        }
+
+        // for tests
+        internal void Reset()
+        {
+            GlobalInstance = new NoopTracerProvider();
+        }
+    }
+}

src/OpenTelemetry.Hosting/Implementation/TelemetryFactoryHostedService.cs

@@ -36,7 +36,7 @@ public Task StartAsync(CancellationToken cancellationToken)
         {
             // Ensure the factory was created when the app starts.
             // This will create and start any configured adapters.
-            this.serviceProvider.GetRequiredService<TracerFactoryBase>();
+            this.serviceProvider.GetRequiredService<ITracerProvider>();
 
             return Task.CompletedTask;
         }