Add CancellationTokenSource pooling

src/ReverseProxy/Service/Proxy/HttpProxy.cs

@@ -122,8 +122,8 @@ public async Task ProxyAsync(
 
                 // :: Step 4: Send the outgoing request using HttpClient
                 HttpResponseMessage destinationResponse;
-                var requestTimeoutSource = CancellationTokenSource.CreateLinkedTokenSource(requestAborted);
-                requestTimeoutSource.CancelAfter(requestOptions?.Timeout ?? DefaultTimeout);
+
+                var requestTimeoutSource = PooledCTS.Rent(requestOptions?.Timeout ?? DefaultTimeout, requestAborted);
                 var requestTimeoutToken = requestTimeoutSource.Token;
                 try
                 {
@@ -151,7 +151,7 @@ public async Task ProxyAsync(
                 }
                 finally
                 {
-                    requestTimeoutSource.Dispose();
+                    requestTimeoutSource.Return();
                 }
 
                 // Detect connection downgrade, which may be problematic for e.g. gRPC.

src/ReverseProxy/Utilities/PooledCTS.cs

@@ -0,0 +1,62 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+#nullable enable
+
+using System;
+using System.Collections.Concurrent;
+using System.Diagnostics;
+using System.Threading;
+
+namespace Yarp.ReverseProxy.Utilities
+{
+    internal sealed class PooledCTS : CancellationTokenSource
+    {
+        private static readonly ConcurrentQueue<PooledCTS> _sharedSources = new();
+
+        private static readonly Action<object?> _linkedTokenCancelDelegate = static s =>
+        {
+            ((CancellationTokenSource)s!).Cancel(throwOnFirstException: false);
+        };
+
+        private const long SafeToReuseTicks = TimeSpan.TicksPerSecond * 10;
+        private static readonly double _stopwatchTicksPerTimeSpanTick = Stopwatch.Frequency / (double)TimeSpan.TicksPerSecond;
+
+        private long _safeToReuseBeforeTimestamp;
+        private CancellationTokenRegistration _registration;
+
+        public static PooledCTS Rent(TimeSpan timeout, CancellationToken linkedToken)
+        {
+            if (!_sharedSources.TryDequeue(out var cts))
+            {
+                cts = new PooledCTS();
+            }
+
+            cts._registration = linkedToken.UnsafeRegister(_linkedTokenCancelDelegate, cts);
+
+            cts._safeToReuseBeforeTimestamp = Stopwatch.GetTimestamp() + (long)((timeout.Ticks - SafeToReuseTicks) * _stopwatchTicksPerTimeSpanTick);
+
+            cts.CancelAfter(timeout);
+
+            return cts;
+        }
+
+        public void Return()
+        {
+            _registration.Dispose();
+            _registration = default;
+
+            // TODO: Use TryReset in 6.0+
+            CancelAfter(Timeout.Infinite);
+
+            if (IsCancellationRequested || Stopwatch.GetTimestamp() > _safeToReuseBeforeTimestamp)
+            {
+                Dispose();
+            }
+            else
+            {
+                _sharedSources.Enqueue(this);
+            }
+        }
+    }
+}