ActivitySource minor optimization and test (#1105)

* ActivitySource minor optimization and test

* comment

* More optimize

src/OpenTelemetry/Trace/ActivitySourceAdapter.cs

@@ -14,6 +14,7 @@
 // limitations under the License.
 // </copyright>
 
+using System;
 using System.Diagnostics;
 using OpenTelemetry.Resources;
 
@@ -39,10 +40,34 @@ namespace OpenTelemetry.Trace
         private readonly Sampler sampler;
         private readonly Resource resource;
         private ActivityProcessor activityProcessor;
+        private Action<Activity> getRequestedDataAction;
 
         internal ActivitySourceAdapter(Sampler sampler, ActivityProcessor activityProcessor, Resource resource)
         {
+            if (sampler == null)
+            {
+                throw new ArgumentNullException(nameof(sampler));
+            }
+
+            if (resource == null)
+            {
+                throw new ArgumentNullException(nameof(resource));
+            }
+
             this.sampler = sampler;
+            if (this.sampler is AlwaysOnSampler)
+            {
+                this.getRequestedDataAction = this.RunGetRequestedDataAlwaysOnSampler;
+            }
+            else if (this.sampler is AlwaysOffSampler)
+            {
+                this.getRequestedDataAction = this.RunGetRequestedDataAlwaysOffSampler;
+            }
+            else
+            {
+                this.getRequestedDataAction = this.RunGetRequestedDataOtherSampler;
+            }
+
             this.activityProcessor = activityProcessor;
             this.resource = resource;
         }
@@ -57,11 +82,11 @@ namespace OpenTelemetry.Trace
         /// <param name="activity"><see cref="Activity"/> to be started.</param>
         public void Start(Activity activity)
         {
-            this.RunGetRequestedData(activity);
+            this.getRequestedDataAction(activity);
             if (activity.IsAllDataRequested)
             {
                 activity.SetResource(this.resource);
-                this.activityProcessor.OnStart(activity);
+                this.activityProcessor?.OnStart(activity);
             }
         }
 
@@ -73,7 +98,7 @@ namespace OpenTelemetry.Trace
         {
             if (activity.IsAllDataRequested)
             {
-                this.activityProcessor.OnEnd(activity);
+                this.activityProcessor?.OnEnd(activity);
             }
         }
 
@@ -82,7 +107,18 @@ namespace OpenTelemetry.Trace
             this.activityProcessor = processor;
         }
 
-        private void RunGetRequestedData(Activity activity)
+        private void RunGetRequestedDataAlwaysOnSampler(Activity activity)
+        {
+            activity.IsAllDataRequested = true;
+            activity.ActivityTraceFlags |= ActivityTraceFlags.Recorded;
+        }
+
+        private void RunGetRequestedDataAlwaysOffSampler(Activity activity)
+        {
+            activity.IsAllDataRequested = false;
+        }
+
+        private void RunGetRequestedDataOtherSampler(Activity activity)
         {
             ActivityContext parentContext;
             if (string.IsNullOrEmpty(activity.ParentId))

test/OpenTelemetry.Tests/Trace/TracerProvideSdkTest.cs

@@ -272,6 +272,31 @@ namespace OpenTelemetry.Trace.Tests
             Assert.True(endCalledNew);
         }
 
+        [Fact]
+        public void TracerProvideSdkCreatesActivitySourceWhenNoProcessor()
+        {
+            TestInstrumentation testInstrumentation = null;
+            using var tracerProvider = Sdk.CreateTracerProviderBuilder()
+                        .AddInstrumentation((adapter) =>
+                        {
+                            testInstrumentation = new TestInstrumentation(adapter);
+                            return testInstrumentation;
+                        })
+                        .Build();
+
+            var adapter = testInstrumentation.Adapter;
+            Activity activity = new Activity("test");
+            activity.Start();
+            adapter.Start(activity);
+            adapter.Stop(activity);
+            activity.Stop();
+
+            // No asserts here. Validates that no exception
+            // gets thrown when processors are not added,
+            // TODO: Refactor to have more proper unit test
+            // to target each individual classes.
+        }
+
         [Fact]
         public void TracerProvideSdkCreatesAndDiposesInstrumentation()
         {