Added sampler to Activity - v1

samples/Exporters/Console/TestConsoleActivity.cs

@@ -49,6 +49,12 @@ internal static object Run(ConsoleActivityOptions options)
                 if (parent != null)
                 {
                     parent.DisplayName = "HttpIn DisplayName";
+
+                    // IsAllDataRequested is equivalent of Span.IsRecording
+                    if (parent.IsAllDataRequested)
+                    {
+                        parent.AddTag("expensive data", "This data is expensive to obtain. Avoid it if activity is not being recorded");
+                    }
                 }
 
                 try

src/OpenTelemetry/Trace/ActivitySampler.cs

@@ -0,0 +1,48 @@
+// <copyright file="ActivitySampler.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.Collections.Generic;
+using System.Diagnostics;
+
+namespace OpenTelemetry.Trace
+{
+    /// <summary>
+    /// Sampler to select data to be exported. This sampler executes before Activity object is created.
+    /// </summary>
+    public abstract class ActivitySampler
+    {
+        /// <summary>
+        /// Gets the sampler description.
+        /// </summary>
+        public abstract string Description { get; }
+
+        /// <summary>
+        /// Checks whether activity needs to be created and tracked.
+        /// </summary>
+        /// <param name="parentContext">Parent activity context. Typically taken from the wire.</param>
+        /// <param name="traceId">Trace ID of a activity to be created.</param>
+        /// <param name="spanId">Span ID of a activity to be created.</param>
+        /// <param name="name"> Name (DisplayName) of the activity to be created. Note, that the name of the activity is settable.
+        /// So this name can be changed later and Sampler implementation should assume that.
+        /// Typical example of a name change is when <see cref="Activity"/> representing incoming http request
+        /// has a name of url path and then being updated with route name when routing complete.
+        /// </param>
+        /// <param name="activityKind">The kind of the Activity.</param>
+        /// <param name="tags">Initial set of Tags for the Activity being constructed.</param>
+        /// <param name="links">Links associated with the activity.</param>
+        /// <returns>Sampling decision on whether activity needs to be sampled or not.</returns>
+        public abstract SamplingResult ShouldSample(in ActivityContext parentContext, in ActivityTraceId traceId, in ActivitySpanId spanId, string name, ActivityKind activityKind, IEnumerable<KeyValuePair<string, string>> tags, IEnumerable<ActivityLink> links);
+    }
+}

src/OpenTelemetry/Trace/Configuration/OpenTelemetryBuilder.cs

@@ -32,6 +32,8 @@ internal OpenTelemetryBuilder()
 
         internal ActivityProcessorPipelineBuilder ProcessingPipeline { get; private set; }
 
+        internal ActivitySampler Sampler { get; private set; }
+
         internal HashSet<string> ActivitySourceNames { get; private set; }
 
         /// <summary>
@@ -52,6 +54,17 @@ public OpenTelemetryBuilder SetProcessorPipeline(Action<ActivityProcessorPipelin
             return this;
         }
 
+        /// <summary>
+        /// Configures sampler.
+        /// </summary>
+        /// <param name="sampler">Sampler instance.</param>
+        /// <returns>Returns <see cref="OpenTelemetryBuilder"/> for chaining.</returns>
+        public OpenTelemetryBuilder SetSampler(ActivitySampler sampler)
+        {
+            this.Sampler = sampler ?? throw new ArgumentNullException(nameof(sampler));
+            return this;
+        }
+
         /// <summary>
         /// Adds given activitysource name to the list of subscribed sources.
         /// </summary>

src/OpenTelemetry/Trace/Configuration/OpenTelemetrySdk.cs

@@ -17,6 +17,7 @@
 using System;
 using System.Diagnostics;
 using OpenTelemetry.Trace.Export;
+using OpenTelemetry.Trace.Samplers;
 
 namespace OpenTelemetry.Trace.Configuration
 {
@@ -40,6 +41,8 @@ public static void EnableOpenTelemetry(Action<OpenTelemetryBuilder> configureOpe
             var openTelemetryBuilder = new OpenTelemetryBuilder();
             configureOpenTelemetryBuilder(openTelemetryBuilder);
 
+            ActivitySampler sampler = openTelemetryBuilder.Sampler ?? new AlwaysOnActivitySampler();
+
             ActivityProcessor activityProcessor;
             if (openTelemetryBuilder.ProcessingPipeline == null)
             {
@@ -65,9 +68,40 @@ public static void EnableOpenTelemetry(Action<OpenTelemetryBuilder> configureOpe
                 // or not
                 ShouldListenTo = (activitySource) => openTelemetryBuilder.ActivitySourceNames.Contains(activitySource.Name.ToUpperInvariant()),
 
-                // The following parameters are not used now.
+                // The following parameter is not used now.
                 GetRequestedDataUsingParentId = (ref ActivityCreationOptions<string> options) => ActivityDataRequest.AllData,
-                GetRequestedDataUsingContext = (ref ActivityCreationOptions<ActivityContext> options) => ActivityDataRequest.AllData,
+
+                // This delegate informs ActivitySource about sampling decision.
+                // Following simple behavior is enabled now:
+                // If Sampler returns IsSampled as true, returns ActivityDataRequest.AllDataAndRecorded
+                // This creates Activity and sets its IsAllDataRequested to true.
+                // Library authors can check activity.IsAllDataRequested and avoid
+                // doing any additional telemetry population.
+                // Activity.IsAllDataRequested is the equivalent of Span.IsRecording
+                //
+                // If Sampler returns IsSampled as false, returns ActivityDataRequest.None
+                // This prevents Activity from being created at all.
+                GetRequestedDataUsingContext = (ref ActivityCreationOptions<ActivityContext> options) =>
+                {
+                    var shouldSample = sampler.ShouldSample(
+                        options.Parent,
+                        options.Parent.TraceId,
+                        default(ActivitySpanId), // Passing default SpanId here. The actual SpanId is not known before actual Activity creation
+                        options.Name,
+                        options.Kind,
+                        options.Tags,
+                        options.Links);
+                    if (shouldSample.IsSampled)
+                    {
+                        return ActivityDataRequest.AllDataAndRecorded;
+                    }
+                    else
+                    {
+                        return ActivityDataRequest.None;
+                    }
+
+                    // TODO: Improve this to properly use ActivityDataRequest.AllData, PropagationData as well.
+                },
             };
 
             ActivitySource.AddActivityListener(listener);

src/OpenTelemetry/Trace/Samplers/AlwaysOffActivitySampler.cs

@@ -0,0 +1,35 @@
+// <copyright file="AlwaysOffActivitySampler.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.Collections.Generic;
+using System.Diagnostics;
+
+namespace OpenTelemetry.Trace.Samplers
+{
+    /// <summary>
+    /// Sampler implementation which never samples any activity.
+    /// </summary>
+    public sealed class AlwaysOffActivitySampler : ActivitySampler
+    {
+        /// <inheritdoc />
+        public override string Description { get; } = nameof(AlwaysOffActivitySampler);
+
+        /// <inheritdoc />
+        public override SamplingResult ShouldSample(in ActivityContext parentContext, in ActivityTraceId traceId, in ActivitySpanId spanId, string name, ActivityKind activityKind, IEnumerable<KeyValuePair<string, string>> tags, IEnumerable<ActivityLink> links)
+        {
+            return new SamplingResult(false);
+        }
+    }
+}

src/OpenTelemetry/Trace/Samplers/AlwaysOnActivitySampler.cs

@@ -0,0 +1,36 @@
+// <copyright file="AlwaysOnActivitySampler.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.Collections.Generic;
+using System.Diagnostics;
+
+namespace OpenTelemetry.Trace.Samplers
+{
+    /// <summary>
+    /// Sampler implementation which samples every activity.
+    /// This sampler will be used as the default Sampler, if no other Sampler is configured.
+    /// </summary>
+    public sealed class AlwaysOnActivitySampler : ActivitySampler
+    {
+        /// <inheritdoc />
+        public override string Description { get; } = nameof(AlwaysOnActivitySampler);
+
+        /// <inheritdoc />
+        public override SamplingResult ShouldSample(in ActivityContext parentContext, in ActivityTraceId traceId, in ActivitySpanId spanId, string name, ActivityKind activityKind, IEnumerable<KeyValuePair<string, string>> tags, IEnumerable<ActivityLink> links)
+        {
+            return new SamplingResult(true);
+        }
+    }
+}

test/OpenTelemetry.Tests/Implementation/Trace/Samplers/ActivitySamplersTest.cs

@@ -0,0 +1,92 @@
+// <copyright file="ActivitySamplersTest.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.Collections.Generic;
+using System.Diagnostics;
+using Xunit;
+
+namespace OpenTelemetry.Trace.Samplers.Test
+{
+    public class ActivitySamplersTest
+    {
+        private static readonly ActivityKind ActivityKindServer = ActivityKind.Server;
+        private readonly ActivityTraceId traceId;
+        private readonly ActivitySpanId spanId;
+        private readonly ActivitySpanId parentSpanId;
+
+        public ActivitySamplersTest()
+        {
+            traceId = ActivityTraceId.CreateRandom();
+            spanId = ActivitySpanId.CreateRandom();
+            parentSpanId = ActivitySpanId.CreateRandom();
+        }
+
+        [Theory]
+        [InlineData(ActivityTraceFlags.Recorded)]
+        [InlineData(ActivityTraceFlags.None)]
+        public void AlwaysOnSampler_AlwaysReturnTrue(ActivityTraceFlags flags)
+        {
+            var parentContext = new ActivityContext(traceId, parentSpanId, flags);
+            var link = new ActivityLink(parentContext);
+
+            Assert.True(
+                    new AlwaysOnActivitySampler()
+                        .ShouldSample(
+                            parentContext,
+                            traceId,
+                            spanId,
+                            "Another name",
+                            ActivityKindServer,
+                            null,
+                            new List<ActivityLink>() { link }).IsSampled);
+        }
+
+        [Fact]
+        public void AlwaysOnSampler_GetDescription()
+        {
+            // TODO: The name must be AlwaysOnSampler as per spec.
+            // We should correct it when we replace span sampler with this.
+            Assert.Equal("AlwaysOnActivitySampler", new AlwaysOnActivitySampler().Description);
+        }
+
+        [Theory]
+        [InlineData(ActivityTraceFlags.Recorded)]
+        [InlineData(ActivityTraceFlags.None)]
+        public void AlwaysOffSampler_AlwaysReturnFalse(ActivityTraceFlags flags)
+        {
+            var parentContext = new ActivityContext(traceId, parentSpanId, flags);
+            var link = new ActivityLink(parentContext);
+
+            Assert.False(
+                    new AlwaysOffActivitySampler()
+                        .ShouldSample(
+                            parentContext,
+                            traceId,
+                            spanId,
+                            "Another name",
+                            ActivityKindServer,
+                            null,
+                            new List<ActivityLink>() { link }).IsSampled);
+        }
+
+        [Fact]
+        public void AlwaysOffSampler_GetDescription()
+        {
+            // TODO: The name must be AlwaysOffSampler as per spec.
+            // We should correct it when we replace span sampler with this.
+            Assert.Equal("AlwaysOffActivitySampler", new AlwaysOffActivitySampler().Description);
+        }
+    }
+}