Implement HedgingResilienceStrategy (#1161)

.github/dependabot.yml

@@ -24,3 +24,4 @@ updates:
     - dependency-name: "Microsoft.Extensions.Logging"
     - dependency-name: "System.Diagnostics.DiagnosticSource"
     - dependency-name: "System.Threading.RateLimiting"
+    - dependency-name: "Microsoft.Bcl.AsyncInterfaces"

src/Directory.Packages.props

@@ -4,6 +4,7 @@
     <PackageVersion Include="BenchmarkDotNet" Version="0.13.5" />
     <PackageVersion Include="FluentAssertions" Version="6.11.0" />
     <PackageVersion Include="GitHubActionsTestLogger" Version="2.0.1" />
+    <PackageVersion Include="Microsoft.Bcl.AsyncInterfaces" Version="1.0.0" />
     <PackageVersion Include="Microsoft.CodeAnalysis.NetAnalyzers" Version="7.0.1" />
     <PackageVersion Include="Microsoft.Extensions.Caching.Memory" Version="7.0.0" />
     <PackageVersion Include="Microsoft.Extensions.DependencyInjection" Version="7.0.0" />
@@ -34,4 +35,4 @@
     <PackageVersion Include="Microsoft.Extensions.Options" Version="2.2.0" />
     <PackageVersion Include="Microsoft.Extensions.Logging.Abstractions" Version="2.2.0" />
   </ItemGroup>
-</Project>
+</Project>

src/Polly.Core.Benchmarks/Benchmarks/HedgingBenchmark.cs

@@ -0,0 +1,42 @@
+using System.Threading.Tasks;
+using BenchmarkDotNet.Attributes;
+using Polly.Core.Benchmarks;
+
+namespace Polly.Benchmarks;
+
+public class HedgingBenchmark
+{
+    private ResilienceStrategy? _strategy;
+
+    [GlobalSetup]
+    public void Setup()
+    {
+        _strategy = Helper.CreateHedging();
+    }
+
+    [Benchmark(Baseline = true)]
+    public async ValueTask Hedging_Primary()
+        => await _strategy!.ExecuteValueTaskAsync(static _ => new ValueTask<string>("primary")).ConfigureAwait(false);
+
+    [Benchmark]
+    public async ValueTask Hedging_Secondary()
+        => await _strategy!.ExecuteValueTaskAsync(static _ => new ValueTask<string>(Helper.Failure)).ConfigureAwait(false);
+
+    [Benchmark]
+    public async ValueTask Hedging_Primary_AsyncWork()
+        => await _strategy!.ExecuteValueTaskAsync(
+            static async _ =>
+            {
+                await Task.Yield();
+                return "primary";
+            }).ConfigureAwait(false);
+
+    [Benchmark]
+    public async ValueTask Hedging_Secondary_AsyncWork()
+        => await _strategy!.ExecuteValueTaskAsync(
+            static async _ =>
+            {
+                await Task.Yield();
+                return Helper.Failure;
+            }).ConfigureAwait(false);
+}

src/Polly.Core.Benchmarks/Internals/Helper.Hedging.cs

@@ -0,0 +1,23 @@
+using Polly.Hedging;
+
+namespace Polly.Core.Benchmarks;
+
+internal static partial class Helper
+{
+    public const string Failure = "failure";
+
+    public static ResilienceStrategy CreateHedging()
+    {
+        return CreateStrategy(builder =>
+        {
+            builder.AddHedging(new HedgingStrategyOptions
+            {
+                Handler = new HedgingHandler().SetHedging<string>(handler =>
+                {
+                    handler.ShouldHandle.HandleResult(Failure);
+                    handler.HedgingActionGenerator = args => () => Task.FromResult("hedged response");
+                })
+            });
+        });
+    }
+}

src/Polly.Core.Benchmarks/README.md

@@ -60,3 +60,12 @@ LaunchCount=2  WarmupCount=10
 |--------------------------- |---------:|----------:|----------:|------:|-------:|----------:|------------:|
 | ExecuteStrategyPipeline_V7 | 1.523 us | 0.0092 us | 0.0137 us |  1.00 | 0.3433 |    2872 B |        1.00 |
 | ExecuteStrategyPipeline_V8 | 1.276 us | 0.0128 us | 0.0191 us |  0.84 | 0.0114 |      96 B |        0.03 |
+
+## HEDGING
+
+|                      Method |       Mean |     Error |    StdDev | Ratio | RatioSD |   Gen0 |   Gen1 | Allocated | Alloc Ratio |
+|---------------------------- |-----------:|----------:|----------:|------:|--------:|-------:|-------:|----------:|------------:|
+|             Hedging_Primary |   891.3 ns |  39.39 ns |  58.96 ns |  1.00 |    0.00 | 0.0048 |      - |      40 B |        1.00 |
+|           Hedging_Secondary | 1,500.0 ns |   7.88 ns |  11.80 ns |  1.69 |    0.11 | 0.0229 |      - |     200 B |        5.00 |
+|   Hedging_Primary_AsyncWork | 4,250.9 ns | 140.89 ns | 206.52 ns |  4.78 |    0.34 | 0.1831 | 0.0305 |    1518 B |       37.95 |
+| Hedging_Secondary_AsyncWork | 6,544.9 ns |  99.90 ns | 143.27 ns |  7.34 |    0.39 | 0.2213 | 0.0839 |    1872 B |       46.80 |

src/Polly.Core.Tests/Hedging/Controller/HedgingControllerTests.cs

@@ -0,0 +1,36 @@
+using Polly.Hedging;
+using Polly.Hedging.Utils;
+
+namespace Polly.Core.Tests.Hedging.Controller;
+
+public class HedgingControllerTests
+{
+    [Fact]
+    public async Task Pooling_Ok()
+    {
+        var handler = new HedgingHandler().SetHedging<int>(handler => handler.HedgingActionGenerator = args => null).CreateHandler();
+        var controller = new HedgingController(new HedgingTimeProvider(), handler!, 3);
+
+        var context1 = controller.GetContext(ResilienceContext.Get());
+        await PrepareAsync(context1);
+
+        var context2 = controller.GetContext(ResilienceContext.Get());
+        await PrepareAsync(context2);
+
+        controller.RentedContexts.Should().Be(2);
+        controller.RentedExecutions.Should().Be(2);
+
+        context1.Complete();
+        context2.Complete();
+
+        controller.RentedContexts.Should().Be(0);
+        controller.RentedExecutions.Should().Be(0);
+    }
+
+    private static async Task PrepareAsync(HedgingExecutionContext context)
+    {
+        await context.LoadExecutionAsync((_, _) => new ValueTask<int>(10), "state");
+        await context.TryWaitForCompletedExecutionAsync(HedgingStrategyOptions.InfiniteHedgingDelay);
+        context.Tasks[0].AcceptOutcome();
+    }
+}