Task delay with infinite timespan is leaking memory

src/Farfetch.LoadShedding/Limiters/AdaptativeConcurrencyLimiter.cs

@@ -59,11 +59,13 @@ public Task ExecuteAsync(Func<Task> function, CancellationToken cancellationToke
         /// </summary>
         public async Task ExecuteAsync(Priority priority, Func<Task> function, CancellationToken cancellationToken = default)
         {
+            using (var delayTaskCancellationSource = new CancellationTokenSource())
+            using (var linkedCancellationSource = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken, delayTaskCancellationSource.Token))
             using (var item = await _taskManager.AcquireAsync(priority, cancellationToken))
             {
                 try
                 {
-                    var delayTask = Task.Delay(Timeout.Infinite, cancellationToken);
+                    var delayTask = Task.Delay(Timeout.Infinite, linkedCancellationSource.Token);
 
                     var resultTask = await Task.WhenAny(
                          function.Invoke(),
@@ -73,6 +75,14 @@ public async Task ExecuteAsync(Priority priority, Func<Task> function, Cancellat
                     {
                         cancellationToken.ThrowIfCancellationRequested();
                     }
+                    else
+                    {
+                        // Stop delayTask, otherwise it is kept indefinetly and leaks CancellationTokenRegistration (DelayPromiseWithCancellation)
+                        delayTaskCancellationSource.Cancel();
+
+                        // await ensures cancellation was received and accepted before we dispose CancellationTokenSource
+                        await delayTask.IgnoreWhenCancelled();
+                    }
 
                     if (resultTask.IsFaulted && resultTask.Exception is not null)
                     {

src/Farfetch.LoadShedding/Tasks/TaskExtensions.cs

@@ -0,0 +1,22 @@
+using System;
+using System.Threading.Tasks;
+
+namespace Farfetch.LoadShedding.Tasks
+{
+    internal static class TaskExtensions
+    {
+        public static async Task IgnoreWhenCancelled(this Task task)
+        {
+            if (!task.IsCanceled)
+            {
+                try
+                {
+                    await task.ConfigureAwait(false);
+                }
+                catch (OperationCanceledException)
+                {
+                }
+            }
+        }
+    }
+}