Introduce TelemetryListener (#1486)

Author: martintmk

bench/Polly.Core.Benchmarks/TelemetryBenchmark.cs

@@ -47,17 +47,7 @@ private ResiliencePipeline Build(ResiliencePipelineBuilder builder)
 
             if (Enrichment)
             {
-                options.Enrichers.Add(context =>
-                {
-                    // The Microsoft.Extensions.Resilience library will add around 6 additional tags
-                    // https://github.com/dotnet/extensions/tree/main/src/Libraries/Microsoft.Extensions.Resilience
-                    context.Tags.Add(new("dummy1", "dummy"));
-                    context.Tags.Add(new("dummy2", "dummy"));
-                    context.Tags.Add(new("dummy3", "dummy"));
-                    context.Tags.Add(new("dummy4", "dummy"));
-                    context.Tags.Add(new("dummy5", "dummy"));
-                    context.Tags.Add(new("dummy6", "dummy"));
-                });
+                options.MeteringEnrichers.Add(new CustomEnricher());
             }
 
             builder.ConfigureTelemetry(options);
@@ -66,6 +56,21 @@ private ResiliencePipeline Build(ResiliencePipelineBuilder builder)
         return builder.Build();
     }
 
+    private class CustomEnricher : MeteringEnricher
+    {
+        public override void Enrich<TResult, TArgs>(in EnrichmentContext<TResult, TArgs> context)
+        {
+            // The Microsoft.Extensions.Resilience library will add around 6 additional tags
+            // https://github.com/dotnet/extensions/tree/main/src/Libraries/Microsoft.Extensions.Resilience
+            context.Tags.Add(new("dummy1", "dummy"));
+            context.Tags.Add(new("dummy2", "dummy"));
+            context.Tags.Add(new("dummy3", "dummy"));
+            context.Tags.Add(new("dummy4", "dummy"));
+            context.Tags.Add(new("dummy5", "dummy"));
+            context.Tags.Add(new("dummy6", "dummy"));
+        }
+    }
+
     private class TelemetryEventStrategy : ResilienceStrategy
     {
         private readonly ResilienceStrategyTelemetry _telemetry;

src/Polly.Core/CircuitBreaker/OnCircuitClosedArguments.cs

@@ -1,12 +1,17 @@
 namespace Polly.CircuitBreaker;
 
+#pragma warning disable CA1815 // Override equals and operator equals on value types
+
 /// <summary>
 /// Arguments used by <see cref="CircuitBreakerStrategyOptions{TResult}.OnClosed"/> event.
 /// </summary>
-public sealed class OnCircuitClosedArguments
+/// <remarks>
+/// Always use the constructor when creating this struct, otherwise we do not guarantee binary compatibility.
+/// </remarks>
+public readonly struct OnCircuitClosedArguments
 {
     /// <summary>
-    /// Initializes a new instance of the <see cref="OnCircuitClosedArguments"/> class.
+    /// Initializes a new instance of the <see cref="OnCircuitClosedArguments"/> struct.
     /// </summary>
     /// <param name="isManual">Indicates whether the circuit was closed manually by using <see cref="CircuitBreakerManualControl"/>.</param>
     public OnCircuitClosedArguments(bool isManual) => IsManual = isManual;

src/Polly.Core/CircuitBreaker/OnCircuitHalfOpenedArguments.cs

@@ -1,12 +1,17 @@
 namespace Polly.CircuitBreaker;
 
+#pragma warning disable CA1815 // Override equals and operator equals on value types
+
 /// <summary>
 /// Arguments used by <see cref="CircuitBreakerStrategyOptions{TResult}.OnHalfOpened"/> event.
 /// </summary>
-public sealed class OnCircuitHalfOpenedArguments
+/// <remarks>
+/// Always use the constructor when creating this struct, otherwise we do not guarantee binary compatibility.
+/// </remarks>
+public readonly struct OnCircuitHalfOpenedArguments
 {
     /// <summary>
-    /// Initializes a new instance of the <see cref="OnCircuitHalfOpenedArguments"/> class.
+    /// Initializes a new instance of the <see cref="OnCircuitHalfOpenedArguments"/> struct.
     /// </summary>
     /// <param name="context">The context instance.</param>
     public OnCircuitHalfOpenedArguments(ResilienceContext context) => Context = context;

src/Polly.Core/CircuitBreaker/OnCircuitOpenedArguments.cs

@@ -1,12 +1,17 @@
 namespace Polly.CircuitBreaker;
 
+#pragma warning disable CA1815 // Override equals and operator equals on value types
+
 /// <summary>
 /// Arguments used by <see cref="CircuitBreakerStrategyOptions{TResult}.OnOpened"/> event.
 /// </summary>
-public sealed class OnCircuitOpenedArguments
+/// <remarks>
+/// Always use the constructor when creating this struct, otherwise we do not guarantee binary compatibility.
+/// </remarks>
+public readonly struct OnCircuitOpenedArguments
 {
     /// <summary>
-    /// Initializes a new instance of the <see cref="OnCircuitOpenedArguments"/> class.
+    /// Initializes a new instance of the <see cref="OnCircuitOpenedArguments"/> struct.
     /// </summary>
     /// <param name="breakDuration">The duration of break.</param>
     /// <param name="isManual">Indicates whether the circuit was opened manually by using <see cref="CircuitBreakerManualControl"/>.</param>

src/Polly.Core/Fallback/FallbackResilienceStrategy.cs

@@ -26,7 +26,7 @@ protected internal override async ValueTask<Outcome<T>> ExecuteCore<TState>(Func
             return outcome;
         }
 
-        var onFallbackArgs = new OutcomeArguments<T, OnFallbackArguments>(context, outcome, new OnFallbackArguments());
+        var onFallbackArgs = new OutcomeArguments<T, OnFallbackArguments>(context, outcome, default);
 
         _telemetry.Report(new(ResilienceEventSeverity.Warning, FallbackConstants.OnFallback), onFallbackArgs);
 

src/Polly.Core/Fallback/OnFallbackArguments.cs

@@ -3,6 +3,9 @@ namespace Polly.Fallback;
 /// <summary>
 /// Represents arguments used in fallback handling scenarios.
 /// </summary>
-public sealed class OnFallbackArguments
+/// <remarks>
+/// Always use the constructor when creating this struct, otherwise we do not guarantee binary compatibility.
+/// </remarks>
+public readonly struct OnFallbackArguments
 {
 }

src/Polly.Core/Hedging/OnHedgingArguments.cs

@@ -1,12 +1,17 @@
 namespace Polly.Hedging;
 
+#pragma warning disable CA1815 // Override equals and operator equals on value types
+
 /// <summary>
 /// Represents arguments used by the on-hedging event.
 /// </summary>
-public sealed class OnHedgingArguments
+/// <remarks>
+/// Always use the constructor when creating this struct, otherwise we do not guarantee binary compatibility.
+/// </remarks>
+public readonly struct OnHedgingArguments
 {
     /// <summary>
-    /// Initializes a new instance of the <see cref="OnHedgingArguments"/> class.
+    /// Initializes a new instance of the <see cref="OnHedgingArguments"/> struct.
     /// </summary>
     /// <param name="attemptNumber">The zero-based hedging attempt number.</param>
     /// <param name="hasOutcome">Indicates whether outcome is available.</param>