Review comments

src/Servers/Kestrel/Core/src/Internal/Http2/FlowControl/InputFlowControl.cs

@@ -19,7 +19,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http2.FlowControl;
 /// <seealso href="https://datatracker.ietf.org/doc/html/rfc9113#name-flow-control"/>
 internal sealed class InputFlowControl
 {
-    private record struct FlowControlState
+    private struct FlowControlState
     {
         private const long AbortedBitMask = 1L << 32; // uint MaxValue + 1
         internal long _state;
@@ -35,7 +35,7 @@ public FlowControlState(uint initialWindowSize, bool isAborted)
 
         public uint Available => (uint)_state;
 
-        public bool IsAborted => (_state & AbortedBitMask) > 0;
+        public bool IsAborted => _state > uint.MaxValue;
     }
 
     private readonly uint _initialWindowSize;
@@ -84,7 +84,7 @@ public bool TryAdvance(int bytes)
                 return false;
             }
 
-            computedFlow = new FlowControlState(currentFlow.Available - (uint)bytes, currentFlow.IsAborted);
+            computedFlow = new FlowControlState(currentFlow.Available - (uint)bytes, isAborted: false);
         } while (currentFlow._state != Interlocked.CompareExchange(ref _flow._state, computedFlow._state, currentFlow._state));
 
         return true;
@@ -110,7 +110,7 @@ public bool TryUpdateWindow(int bytes, out int updateSize)
                 // It shouldn't be possible for the window size to ever exceed Http2PeerSettings.MaxWindowSize.
                 Debug.Assert(false, $"{nameof(TryUpdateWindow)} attempted to grow window past max size.");
             }
-            computedFlow = new FlowControlState(currentFlow.Available + (uint)bytes, currentFlow.IsAborted);
+            computedFlow = new FlowControlState(currentFlow.Available + (uint)bytes, isAborted: false);
         } while (currentFlow._state != Interlocked.CompareExchange(ref _flow._state, computedFlow._state, currentFlow._state));
 
         if (_windowUpdatesDisabled)
@@ -156,7 +156,7 @@ public int Abort()
                 return 0;
             }
 
-            computedFlow = new FlowControlState(currentFlow.Available, true);
+            computedFlow = new FlowControlState(currentFlow.Available, isAborted: true);
         } while (currentFlow._state != Interlocked.CompareExchange(ref _flow._state, computedFlow._state, currentFlow._state));
 
         // Tell caller to return connection window space consumed by this stream. Even if window updates have

src/Servers/Kestrel/Core/test/Http2/FlowControl/InputFlowControlTests.cs

@@ -8,10 +8,12 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Tests.Http2.FlowControl;
 
 public class InputFlowControlTests
 {
+    private const int IterationCount = 1;
+
     [Fact]
     public async Task Threads1_Advance()
     {
-        for (var i = 0; i < 1000; i++)
+        for (var i = 0; i < IterationCount; i++)
         {
             var sut = new InputFlowControl(5000, 1);
             await Task.Run(() => Advance(sut)); ;
@@ -30,7 +32,7 @@ static void Advance(InputFlowControl sut)
     [Fact]
     public async Task Threads2_Advance()
     {
-        for (var i = 0; i < 1000; i++)
+        for (var i = 0; i < IterationCount; i++)
         {
             var sut = new InputFlowControl(10000, 1);
             var t1 = Task.Run(() => Advance(sut));
@@ -51,7 +53,7 @@ static void Advance(InputFlowControl sut)
     [Fact]
     public async Task Threads3_Advance()
     {
-        for (var i = 0; i < 1000; i++)
+        for (var i = 0; i < IterationCount; i++)
         {
             var sut = new InputFlowControl(15000, 1);
             var t1 = Task.Run(() => Advance(sut));
@@ -73,7 +75,7 @@ static void Advance(InputFlowControl sut)
     [Fact]
     public async Task Threads3_WindowUpdates()
     {
-        for (var i = 0; i < 1000; i++)
+        for (var i = 0; i < IterationCount; i++)
         {
             var sut = new InputFlowControl(15000, 0);
             var t1 = Task.Run(() => WindowUpdate(sut));
@@ -96,7 +98,7 @@ static void WindowUpdate(InputFlowControl sut)
     [Fact]
     public async Task Threads4_Advance()
     {
-        for (var i = 0; i < 1000; i++)
+        for (var i = 0; i < IterationCount; i++)
         {
             var sut = new InputFlowControl(20000, 1);
             var t1 = Task.Run(() => Advance(sut));
@@ -118,7 +120,7 @@ static void Advance(InputFlowControl sut)
     [Fact]
     public async Task Threads3_Abort()
     {
-        for (var i = 0; i < 1000; i++)
+        for (var i = 0; i < IterationCount; i++)
         {
             var sut = new InputFlowControl(20000, 1);
             var t1 = Task.Run(() => Advance(sut));
@@ -165,7 +167,7 @@ public void Abort_Abort()
     [Fact]
     public async Task Threads3Abort_AssertAfter()
     {
-        for (var i = 0; i < 1000; i++)
+        for (var i = 0; i < IterationCount; i++)
         {
             var isAborted = false;
             var sut = new InputFlowControl(90000, 1);
@@ -204,7 +206,7 @@ static void Advance(ref bool isAborted, InputFlowControl sut)
     [Fact]
     public async Task Threads3Abort_AssertBefore()
     {
-        for (var i = 0; i < 3000; i++)
+        for (var i = 0; i < IterationCount; i++)
         {
             var isAborting = false;
             var sut = new InputFlowControl(30000, 1);
@@ -243,7 +245,7 @@ static void Advance(ref bool isAborting, InputFlowControl sut)
     [Fact]
     public async Task Threads3WindowUpdates_AssertAfter()
     {
-        for (var i = 0; i < 1000; i++)
+        for (var i = 0; i < IterationCount; i++)
         {
             var isAborted = false;
             var sut = new InputFlowControl(90000, 1);
@@ -282,7 +284,7 @@ static void WindowUpdate(ref bool isAborted, InputFlowControl sut)
     [Fact]
     public async Task Threads3WindowUpdates_AssertBefore()
     {
-        for (var i = 0; i < 3000; i++)
+        for (var i = 0; i < IterationCount; i++)
         {
             var isAborting = false;
             var sut = new InputFlowControl(30000, 1);
@@ -321,7 +323,7 @@ static void WindowUpdate(ref bool isAborting, InputFlowControl sut)
     [Fact]
     public async Task Threads3Advance_WindowUpdates()
     {
-        for (var i = 0; i < 1000; i++)
+        for (var i = 0; i < IterationCount; i++)
         {
             var sut = new InputFlowControl(30000, 0);
             var t0 = Task.Run(() => WindowUpdate(sut));
@@ -354,7 +356,7 @@ static void Advance(InputFlowControl sut)
     [Fact]
     public async Task Threads3WindowUpdates_AssertSize()
     {
-        for (var i = 0; i < 1000; i++)
+        for (var i = 0; i < IterationCount; i++)
         {
             var sizeSum = 0;
             var sut = new InputFlowControl(15000, 10);

src/Servers/Kestrel/perf/Microbenchmarks/Http2/FlowControl/FlowControlBenchmark.cs

@@ -0,0 +1,55 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using BenchmarkDotNet.Attributes;
+using Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http2.FlowControl;
+
+namespace Microsoft.AspNetCore.Server.Kestrel.Microbenchmarks.Http2.FlowControl;
+
+public class FlowControlBenchmark
+{
+    private readonly InputFlowControl _flowControl = new(1000, 10);
+    private const int N = 100000;
+    private const int Spin = 50;
+    private const int ThreadsCount = 3;
+
+    [IterationSetup]
+    public void IterationSetup()
+    {
+        _flowControl.Reset();
+    }
+
+    [Benchmark]
+    public async Task ThreadsAdvanceWithWindowUpdates()
+    {
+        var parallelThreads = new Task[ThreadsCount + 1];
+        _flowControl.Reset();
+        for (var i = 0; i < ThreadsCount; i++)
+        {
+            var advanceTask = Task.Factory.StartNew(() =>
+            {
+                for (int i = 0; i < N; i++)
+                {
+                    if (_flowControl.TryUpdateWindow(16, out _))
+                    {
+                        for (int j = 0; j < Spin; j++)
+                        {
+                        }
+                    }
+                }
+            }, TaskCreationOptions.LongRunning);
+            parallelThreads[i] = advanceTask;
+            var tAdvance = Task.Factory.StartNew(() =>
+            {
+                for (var i = 0; i < N; i++)
+                {
+                    _flowControl.TryAdvance(1);
+                }
+                _flowControl.Abort();
+            }, TaskCreationOptions.LongRunning);
+            parallelThreads[ThreadsCount] = tAdvance;
+        }
+
+        await Task.WhenAll(parallelThreads);
+    }
+}