Add doc comments for Samplers.

src/OpenTelemetry/Trace/Samplers/AlwaysOffSampler.cs

@@ -18,8 +18,12 @@
 
 namespace OpenTelemetry.Trace.Samplers
 {
+    /// <summary>
+    /// Sampler implementation which will sample out all the spans.
+    /// </summary>
     public sealed class AlwaysOffSampler : Sampler
     {
+        /// <inheritdoc />
         public override string Description { get; } = nameof(AlwaysOffSampler);
 
         /// <inheritdoc />

src/OpenTelemetry/Trace/Samplers/AlwaysOnSampler.cs

@@ -18,8 +18,13 @@
 
 namespace OpenTelemetry.Trace.Samplers
 {
+    /// <summary>
+    /// Sampler implementation which will sample in all the spans.
+    /// This sampler will be used as the default Sampler, if no other Sampler is configured.
+    /// </summary>
     public sealed class AlwaysOnSampler : Sampler
     {
+        /// <inheritdoc />
         public override string Description { get; } = nameof(AlwaysOnSampler);
 
         /// <inheritdoc />

src/OpenTelemetry/Trace/Samplers/AlwaysParentSampler.cs

@@ -18,8 +18,13 @@
 
 namespace OpenTelemetry.Trace.Samplers
 {
+    /// <summary>
+    /// Sampler implementation which will sample in, if parent span is sampled in.
+    /// If parent span is invalid, span is sampled out.
+    /// </summary>
     public sealed class AlwaysParentSampler : Sampler
     {
+        /// <inheritdoc />
         public override string Description { get; } = nameof(AlwaysParentSampler);
 
         /// <inheritdoc />

src/OpenTelemetry/Trace/Samplers/ProbabilitySampler.cs

@@ -19,12 +19,22 @@
 
 namespace OpenTelemetry.Trace.Samplers
 {
-    /// <inheritdoc />
+    /// <summary>
+    /// Sampler implementation which will sample in, if parent span or any linked span is sampled in.
+    /// Otherwise, samples in a percentage of the spans.
+    /// The probability of sampling a span is equal to that of the specified probability.
+    /// </summary>
     public sealed class ProbabilitySampler : Sampler
     {
         private readonly long idUpperBound;
         private readonly double probability;
 
+        /// <summary>
+        /// Initializes a new instance of the <see cref="ProbabilitySampler"/> class.
+        /// </summary>
+        /// <param name="probability">The desired probability of sampling. This must be between 0.0 and 1.0.
+        /// Higher the value, higher is the probability of a given span to be sampled in.
+        /// </param>
         public ProbabilitySampler(double probability)
         {
             if (probability < 0.0 || probability > 1.0)
@@ -33,7 +43,10 @@ public ProbabilitySampler(double probability)
             }
 
             this.probability = probability;
-            this.Description = $"ProbabilitySampler({this.probability:F6})";
+
+            // The expected description is like ProbabilitySampler{0.000100}
+            // https://docs.microsoft.com/dotnet/standard/base-types/composite-formatting#escaping-braces
+            this.Description = string.Format("{0}{1:F6}{2}", "ProbabilitySampler{", this.probability, "}");
 
             // Special case the limits, to avoid any possible issues with lack of precision across
             // double/long boundaries. For probability == 0.0, we use Long.MIN_VALUE as this guarantees

test/OpenTelemetry.Tests/Impl/Trace/Samplers/SamplersTest.cs

@@ -254,7 +254,8 @@ public void ProbabilitySampler_SampleBasedOnTraceId()
         [Fact]
         public void ProbabilitySampler_GetDescription()
         {
-            Assert.Equal($"ProbabilitySampler({0.5:F6})", new ProbabilitySampler(0.5).Description);
+            var expectedDescription = "ProbabilitySampler{0.500000}";
+            Assert.Equal(expectedDescription, new ProbabilitySampler(0.5).Description);
         }
 
         // Applies the given sampler to NUM_SAMPLE_TRIES random traceId/spanId pairs.