Expose Randomizer property and use it in retry strategy

src/Polly.Core/ResilienceStrategyBuilderBase.cs

@@ -27,6 +27,8 @@ private protected ResilienceStrategyBuilderBase(ResilienceStrategyBuilderBase ot
         Properties = other.Properties;
         TimeProvider = other.TimeProvider;
         OnCreatingStrategy = other.OnCreatingStrategy;
+        Randomizer = other.Randomizer;
+        DiagnosticSource = other.DiagnosticSource;
     }
 
     /// <summary>
@@ -70,6 +72,16 @@ private protected ResilienceStrategyBuilderBase(ResilienceStrategyBuilderBase ot
     [EditorBrowsable(EditorBrowsableState.Never)]
     public DiagnosticSource? DiagnosticSource { get; set; }
 
+    /// <summary>
+    /// Gets or sets the randomizer that is used by strategies that need to generate random numbers.
+    /// </summary>
+    /// <remarks>
+    /// The default randomizer is thread safe and returns values between 0.0 and 1.0.
+    /// </remarks>
+    [EditorBrowsable(EditorBrowsableState.Never)]
+    [Required]
+    public Func<double> Randomizer { get; set; } = RandomUtil.Instance.NextDouble;
+
     internal abstract bool IsGenericBuilder { get; }
 
     internal void AddStrategyCore(Func<ResilienceStrategyBuilderContext, ResilienceStrategy> factory, ResilienceStrategyOptions options)
@@ -118,7 +130,8 @@ private ResilienceStrategy CreateResilienceStrategy(Entry entry)
             strategyType: entry.Properties.StrategyType,
             timeProvider: TimeProvider,
             isGenericBuilder: IsGenericBuilder,
-            diagnosticSource: DiagnosticSource);
+            diagnosticSource: DiagnosticSource,
+            randomizer: Randomizer);
 
         return entry.Factory(context);
     }

src/Polly.Core/ResilienceStrategyBuilderContext.cs

@@ -2,6 +2,8 @@
 
 namespace Polly;
 
+#pragma warning disable S107
+
 /// <summary>
 /// The context used for building an individual resilience strategy.
 /// </summary>
@@ -14,7 +16,8 @@ internal ResilienceStrategyBuilderContext(
         string strategyType,
         TimeProvider timeProvider,
         bool isGenericBuilder,
-        DiagnosticSource? diagnosticSource)
+        DiagnosticSource? diagnosticSource,
+        Func<double> randomizer)
     {
         BuilderName = builderName;
         BuilderProperties = builderProperties;
@@ -23,6 +26,7 @@ internal ResilienceStrategyBuilderContext(
         TimeProvider = timeProvider;
         IsGenericBuilder = isGenericBuilder;
         Telemetry = TelemetryUtil.CreateTelemetry(diagnosticSource, builderName, builderProperties, strategyName, strategyType);
+        Randomizer = randomizer;
     }
 
     /// <summary>
@@ -55,5 +59,7 @@ internal ResilienceStrategyBuilderContext(
     /// </summary>
     internal TimeProvider TimeProvider { get; }
 
+    internal Func<double> Randomizer { get; }
+
     internal bool IsGenericBuilder { get; }
 }

src/Polly.Core/Retry/RetryHelper.cs

@@ -6,7 +6,7 @@ internal static class RetryHelper
 
     public static bool IsValidDelay(TimeSpan delay) => delay >= TimeSpan.Zero;
 
-    public static TimeSpan GetRetryDelay(RetryBackoffType type, int attempt, TimeSpan baseDelay, ref double state, RandomUtil random)
+    public static TimeSpan GetRetryDelay(RetryBackoffType type, int attempt, TimeSpan baseDelay, ref double state, Func<double> randomizer)
     {
         if (baseDelay == TimeSpan.Zero)
         {
@@ -23,7 +23,7 @@ public static TimeSpan GetRetryDelay(RetryBackoffType type, int attempt, TimeSpa
             RetryBackoffType.Linear => (attempt + 1) * baseDelay,
             RetryBackoffType.Exponential => Math.Pow(ExponentialFactor, attempt) * baseDelay,
 #endif
-            RetryBackoffType.ExponentialWithJitter => DecorrelatedJitterBackoffV2(attempt, baseDelay, ref state, random),
+            RetryBackoffType.ExponentialWithJitter => DecorrelatedJitterBackoffV2(attempt, baseDelay, ref state, randomizer),
             _ => throw new ArgumentOutOfRangeException(nameof(type), type, "The retry backoff type is not supported.")
         };
     }
@@ -40,11 +40,11 @@ public static TimeSpan GetRetryDelay(RetryBackoffType type, int attempt, TimeSpa
     /// The actual amount of delay-before-retry for try t may be distributed between 0 and <c>f * (2^(t+1) - 2^(t-1)) for t >= 2;</c>
     /// or between 0 and <c>f * 2^(t+1)</c>, for t is 0 or 1.</param>
     /// <param name="prev">The previous state value used for calculations.</param>
-    /// <param name="random">The random utility to use.</param>
+    /// <param name="randomizer">The generator to use.</param>
     /// <remarks>
     /// This code was adopted from https://github.com/Polly-Contrib/Polly.Contrib.WaitAndRetry/blob/master/src/Polly.Contrib.WaitAndRetry/Backoff.DecorrelatedJitterV2.cs.
     /// </remarks>
-    private static TimeSpan DecorrelatedJitterBackoffV2(int attempt, TimeSpan baseDelay, ref double prev, RandomUtil random)
+    private static TimeSpan DecorrelatedJitterBackoffV2(int attempt, TimeSpan baseDelay, ref double prev, Func<double> randomizer)
     {
         // The original author/credit for this jitter formula is @george-polevoy .
         // Jitter formula used with permission as described at https://github.com/App-vNext/Polly/issues/530#issuecomment-526555979
@@ -64,7 +64,7 @@ private static TimeSpan DecorrelatedJitterBackoffV2(int attempt, TimeSpan baseDe
 
         long targetTicksFirstDelay = baseDelay.Ticks;
 
-        double t = attempt + random.NextDouble();
+        double t = attempt + randomizer();
         double next = Math.Pow(2, t) * Math.Tanh(Math.Sqrt(PFactor * t));
 
         double formulaIntrinsicValue = next - prev;

src/Polly.Core/Retry/RetryResilienceStrategy.cs

@@ -1,3 +1,4 @@
+using System;
 using Polly.Telemetry;
 
 namespace Polly.Retry;
@@ -6,14 +7,14 @@ internal sealed class RetryResilienceStrategy<T> : OutcomeResilienceStrategy<T>
 {
     private readonly TimeProvider _timeProvider;
     private readonly ResilienceStrategyTelemetry _telemetry;
-    private readonly RandomUtil _randomUtil;
+    private readonly Func<double> _randomizer;
 
     public RetryResilienceStrategy(
         RetryStrategyOptions<T> options,
         bool isGeneric,
         TimeProvider timeProvider,
         ResilienceStrategyTelemetry telemetry,
-        RandomUtil randomUtil)
+        Func<double> randomizer)
         : base(isGeneric)
     {
         ShouldHandle = options.ShouldHandle;
@@ -25,7 +26,7 @@ public RetryResilienceStrategy(
 
         _timeProvider = timeProvider;
         _telemetry = telemetry;
-        _randomUtil = randomUtil;
+        _randomizer = randomizer;
     }
 
     public TimeSpan BaseDelay { get; }
@@ -61,7 +62,7 @@ protected override async ValueTask<Outcome<T>> ExecuteCallbackAsync<TState>(Func
                 return outcome;
             }
 
-            var delay = RetryHelper.GetRetryDelay(BackoffType, attempt, BaseDelay, ref retryState, _randomUtil);
+            var delay = RetryHelper.GetRetryDelay(BackoffType, attempt, BaseDelay, ref retryState, _randomizer);
             if (DelayGenerator is not null)
             {
                 var delayArgs = new OutcomeArguments<T, RetryDelayArguments>(context, outcome, new RetryDelayArguments(attempt, delay));

src/Polly.Core/Retry/RetryResilienceStrategyBuilderExtensions.cs

@@ -50,7 +50,7 @@ private static TBuilder AddRetryCore<TBuilder, TResult>(this TBuilder builder, R
                 context.IsGenericBuilder,
                 context.TimeProvider,
                 context.Telemetry,
-                RandomUtil.Instance),
+                context.Randomizer),
             options);
     }
 }

test/Polly.Core.Tests/ResilienceStrategyBuilderContextTests.cs

@@ -9,7 +9,7 @@ public void Ctor_EnsureDefaults()
     {
         var properties = new ResilienceProperties();
         var timeProvider = new FakeTimeProvider();
-        var context = new ResilienceStrategyBuilderContext("builder-name", properties, "strategy-name", "strategy-type", timeProvider.Object, true, Mock.Of<DiagnosticSource>());
+        var context = new ResilienceStrategyBuilderContext("builder-name", properties, "strategy-name", "strategy-type", timeProvider.Object, true, Mock.Of<DiagnosticSource>(), () => 1.0);
 
         context.IsGenericBuilder.Should().BeTrue();
         context.BuilderName.Should().Be("builder-name");
@@ -18,6 +18,7 @@ public void Ctor_EnsureDefaults()
         context.StrategyType.Should().Be("strategy-type");
         context.TimeProvider.Should().Be(timeProvider.Object);
         context.Telemetry.Should().NotBeNull();
+        context.Randomizer.Should().NotBeNull();
 
         context.Telemetry.TelemetrySource.BuilderName.Should().Be("builder-name");
         context.Telemetry.TelemetrySource.BuilderProperties.Should().BeSameAs(properties);

test/Polly.Core.Tests/ResilienceStrategyBuilderTests.cs

@@ -1,4 +1,5 @@
 using System.ComponentModel.DataAnnotations;
+using Moq;
 using Polly.Utils;
 
 namespace Polly.Core.Tests;
@@ -14,6 +15,30 @@ public void Ctor_EnsureDefaults()
         builder.Properties.Should().NotBeNull();
         builder.TimeProvider.Should().Be(TimeProvider.System);
         builder.IsGenericBuilder.Should().BeFalse();
+        builder.Randomizer.Should().NotBeNull();
+    }
+
+    [Fact]
+    public void CopyCtor_Ok()
+    {
+        var builder = new ResilienceStrategyBuilder
+        {
+            TimeProvider = Mock.Of<TimeProvider>(),
+            BuilderName = "dummy",
+            Randomizer = () => 0.0,
+            DiagnosticSource = Mock.Of<DiagnosticSource>(),
+            OnCreatingStrategy = _ => { },
+        };
+
+        builder.Properties.Set(new ResiliencePropertyKey<string>("dummy"), "dummy");
+
+        var other = new ResilienceStrategyBuilder<double>(builder);
+        other.BuilderName.Should().Be(builder.BuilderName);
+        other.TimeProvider.Should().Be(builder.TimeProvider);
+        other.Randomizer.Should().BeSameAs(builder.Randomizer);
+        other.DiagnosticSource.Should().BeSameAs(builder.DiagnosticSource);
+        other.OnCreatingStrategy.Should().BeSameAs(builder.OnCreatingStrategy);
+        other.Properties.GetValue(new ResiliencePropertyKey<string>("dummy"), "").Should().Be("dummy");
     }
 
     [Fact]
@@ -133,10 +158,7 @@ public void AddStrategy_MultipleNonDelegating_Ok()
     }
 
     [Fact]
-    public void Build_Empty_ReturnsNullResilienceStrategy()
-    {
-        new ResilienceStrategyBuilder().Build().Should().BeSameAs(NullResilienceStrategy.Instance);
-    }
+    public void Build_Empty_ReturnsNullResilienceStrategy() => new ResilienceStrategyBuilder().Build().Should().BeSameAs(NullResilienceStrategy.Instance);
 
     [Fact]
     public void AddStrategy_AfterUsed_Throws()
@@ -259,6 +281,7 @@ public void BuildStrategy_EnsureCorrectContext()
                 context.BuilderProperties.Should().BeSameAs(builder.Properties);
                 context.Telemetry.Should().NotBeNull();
                 context.TimeProvider.Should().Be(builder.TimeProvider);
+                context.Randomizer.Should().BeSameAs(builder.Randomizer);
                 verified1 = true;
 
                 return new TestResilienceStrategy();
@@ -312,10 +335,7 @@ public void Build_OnCreatingStrategy_EnsureRespected()
     }
 
     [Fact]
-    public void EmptyOptions_Ok()
-    {
-        ResilienceStrategyBuilderExtensions.EmptyOptions.Instance.StrategyType.Should().Be("Empty");
-    }
+    public void EmptyOptions_Ok() => ResilienceStrategyBuilderExtensions.EmptyOptions.Instance.StrategyType.Should().Be("Empty");
 
     [Fact]
     public void ExecuteAsync_EnsureReceivedCallbackExecutesNextStrategy()

test/Polly.Core.Tests/Retry/RetryHelperTests.cs

@@ -6,7 +6,7 @@ namespace Polly.Core.Tests.Retry;
 
 public class RetryHelperTests
 {
-    private readonly RandomUtil _randomUtil = new(0);
+    private readonly Func<double> _randomizer = new RandomUtil(0).NextDouble;
 
     [Fact]
     public void IsValidDelay_Ok()
@@ -26,7 +26,7 @@ public void UnsupportedRetryBackoffType_Throws()
         Assert.Throws<ArgumentOutOfRangeException>(() =>
         {
             double state = 0;
-            return RetryHelper.GetRetryDelay(type, 0, TimeSpan.FromSeconds(1), ref state, _randomUtil);
+            return RetryHelper.GetRetryDelay(type, 0, TimeSpan.FromSeconds(1), ref state, _randomizer);
         });
     }
 
@@ -35,41 +35,41 @@ public void Constant_Ok()
     {
         double state = 0;
 
-        RetryHelper.GetRetryDelay(RetryBackoffType.Constant, 0, TimeSpan.Zero, ref state, _randomUtil).Should().Be(TimeSpan.Zero);
-        RetryHelper.GetRetryDelay(RetryBackoffType.Constant, 1, TimeSpan.Zero, ref state, _randomUtil).Should().Be(TimeSpan.Zero);
-        RetryHelper.GetRetryDelay(RetryBackoffType.Constant, 2, TimeSpan.Zero, ref state, _randomUtil).Should().Be(TimeSpan.Zero);
+        RetryHelper.GetRetryDelay(RetryBackoffType.Constant, 0, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
+        RetryHelper.GetRetryDelay(RetryBackoffType.Constant, 1, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
+        RetryHelper.GetRetryDelay(RetryBackoffType.Constant, 2, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
 
-        RetryHelper.GetRetryDelay(RetryBackoffType.Constant, 0, TimeSpan.FromSeconds(1), ref state, _randomUtil).Should().Be(TimeSpan.FromSeconds(1));
-        RetryHelper.GetRetryDelay(RetryBackoffType.Constant, 1, TimeSpan.FromSeconds(1), ref state, _randomUtil).Should().Be(TimeSpan.FromSeconds(1));
-        RetryHelper.GetRetryDelay(RetryBackoffType.Constant, 2, TimeSpan.FromSeconds(1), ref state, _randomUtil).Should().Be(TimeSpan.FromSeconds(1));
+        RetryHelper.GetRetryDelay(RetryBackoffType.Constant, 0, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(1));
+        RetryHelper.GetRetryDelay(RetryBackoffType.Constant, 1, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(1));
+        RetryHelper.GetRetryDelay(RetryBackoffType.Constant, 2, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(1));
     }
 
     [Fact]
     public void Linear_Ok()
     {
         double state = 0;
 
-        RetryHelper.GetRetryDelay(RetryBackoffType.Linear, 0, TimeSpan.Zero, ref state, _randomUtil).Should().Be(TimeSpan.Zero);
-        RetryHelper.GetRetryDelay(RetryBackoffType.Linear, 1, TimeSpan.Zero, ref state, _randomUtil).Should().Be(TimeSpan.Zero);
-        RetryHelper.GetRetryDelay(RetryBackoffType.Linear, 2, TimeSpan.Zero, ref state, _randomUtil).Should().Be(TimeSpan.Zero);
+        RetryHelper.GetRetryDelay(RetryBackoffType.Linear, 0, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
+        RetryHelper.GetRetryDelay(RetryBackoffType.Linear, 1, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
+        RetryHelper.GetRetryDelay(RetryBackoffType.Linear, 2, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
 
-        RetryHelper.GetRetryDelay(RetryBackoffType.Linear, 0, TimeSpan.FromSeconds(1), ref state, _randomUtil).Should().Be(TimeSpan.FromSeconds(1));
-        RetryHelper.GetRetryDelay(RetryBackoffType.Linear, 1, TimeSpan.FromSeconds(1), ref state, _randomUtil).Should().Be(TimeSpan.FromSeconds(2));
-        RetryHelper.GetRetryDelay(RetryBackoffType.Linear, 2, TimeSpan.FromSeconds(1), ref state, _randomUtil).Should().Be(TimeSpan.FromSeconds(3));
+        RetryHelper.GetRetryDelay(RetryBackoffType.Linear, 0, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(1));
+        RetryHelper.GetRetryDelay(RetryBackoffType.Linear, 1, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(2));
+        RetryHelper.GetRetryDelay(RetryBackoffType.Linear, 2, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(3));
     }
 
     [Fact]
     public void Exponential_Ok()
     {
         double state = 0;
 
-        RetryHelper.GetRetryDelay(RetryBackoffType.Exponential, 0, TimeSpan.Zero, ref state, _randomUtil).Should().Be(TimeSpan.Zero);
-        RetryHelper.GetRetryDelay(RetryBackoffType.Exponential, 1, TimeSpan.Zero, ref state, _randomUtil).Should().Be(TimeSpan.Zero);
-        RetryHelper.GetRetryDelay(RetryBackoffType.Exponential, 2, TimeSpan.Zero, ref state, _randomUtil).Should().Be(TimeSpan.Zero);
+        RetryHelper.GetRetryDelay(RetryBackoffType.Exponential, 0, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
+        RetryHelper.GetRetryDelay(RetryBackoffType.Exponential, 1, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
+        RetryHelper.GetRetryDelay(RetryBackoffType.Exponential, 2, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
 
-        RetryHelper.GetRetryDelay(RetryBackoffType.Exponential, 0, TimeSpan.FromSeconds(1), ref state, _randomUtil).Should().Be(TimeSpan.FromSeconds(1));
-        RetryHelper.GetRetryDelay(RetryBackoffType.Exponential, 1, TimeSpan.FromSeconds(1), ref state, _randomUtil).Should().Be(TimeSpan.FromSeconds(2));
-        RetryHelper.GetRetryDelay(RetryBackoffType.Exponential, 2, TimeSpan.FromSeconds(1), ref state, _randomUtil).Should().Be(TimeSpan.FromSeconds(4));
+        RetryHelper.GetRetryDelay(RetryBackoffType.Exponential, 0, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(1));
+        RetryHelper.GetRetryDelay(RetryBackoffType.Exponential, 1, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(2));
+        RetryHelper.GetRetryDelay(RetryBackoffType.Exponential, 2, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(4));
     }
 
     [InlineData(1)]
@@ -94,20 +94,20 @@ public void ExponentialWithJitter_Ok(int count)
     public void ExponentialWithJitter_EnsureRandomness()
     {
         var delay = TimeSpan.FromSeconds(7.8);
-        var delays1 = GetExponentialWithJitterBackoff(false, delay, 100, RandomUtil.Instance);
-        var delays2 = GetExponentialWithJitterBackoff(false, delay, 100, RandomUtil.Instance);
+        var delays1 = GetExponentialWithJitterBackoff(false, delay, 100, RandomUtil.Instance.NextDouble);
+        var delays2 = GetExponentialWithJitterBackoff(false, delay, 100, RandomUtil.Instance.NextDouble);
 
         delays1.SequenceEqual(delays2).Should().BeFalse();
     }
 
-    private static IReadOnlyList<TimeSpan> GetExponentialWithJitterBackoff(bool contrib, TimeSpan baseDelay, int retryCount, RandomUtil? util = null)
+    private static IReadOnlyList<TimeSpan> GetExponentialWithJitterBackoff(bool contrib, TimeSpan baseDelay, int retryCount, Func<double>? randomizer = null)
     {
         if (contrib)
         {
             return Backoff.DecorrelatedJitterBackoffV2(baseDelay, retryCount, 0, false).Take(retryCount).ToArray();
         }
 
-        var random = util ?? new RandomUtil(0);
+        var random = randomizer ?? new RandomUtil(0).NextDouble;
         double state = 0;
         var result = new List<TimeSpan>();
 

test/Polly.Core.Tests/Retry/RetryResilienceStrategyBuilderExtensionsTests.cs

@@ -103,4 +103,48 @@ public void AddRetry_InvalidOptions_Throws()
             .Should()
             .Throw<ValidationException>();
     }
+
+    [Fact]
+    public void GetAggregatedDelay_ShouldReturnTheSameValue()
+    {
+        var options = new RetryStrategyOptions { BackoffType = RetryBackoffType.ExponentialWithJitter };
+
+        var delay = GetAggregatedDelay(options);
+        GetAggregatedDelay(options).Should().Be(delay);
+    }
+
+    [Fact]
+    public void GetAggregatedDelay_EnsureCorrectValue()
+    {
+        var options = new RetryStrategyOptions { BackoffType = RetryBackoffType.Constant, BaseDelay = TimeSpan.FromSeconds(1), RetryCount = 5 };
+
+        GetAggregatedDelay(options).Should().Be(TimeSpan.FromSeconds(5));
+    }
+
+    private static TimeSpan GetAggregatedDelay<T>(RetryStrategyOptions<T> options)
+    {
+        var aggregatedDelay = TimeSpan.Zero;
+
+        var strategy = new ResilienceStrategyBuilder { Randomizer = () => 1.0 }.AddRetry(new()
+        {
+            RetryCount = options.RetryCount,
+            BaseDelay = options.BaseDelay,
+            BackoffType = options.BackoffType,
+            ShouldHandle = _ => PredicateResult.True, // always retry until all retries are exhausted
+            RetryDelayGenerator = args =>
+            {
+                // the delay hint is calculated for this attempt by the retry strategy
+                aggregatedDelay += args.Arguments.DelayHint;
+
+                // return zero delay, so no waiting
+                return new ValueTask<TimeSpan>(TimeSpan.Zero);
+            }
+        })
+        .Build();
+
+        // this executes all retries and we aggregate the delays immediately
+        strategy.Execute(() => { });
+
+        return aggregatedDelay;
+    }
 }