Slow invocation of read callbacks

CHANGELOG.md

@@ -1,5 +1,13 @@
 # ChangeLog - DataStax C# Driver
 
+## 3.23.0
+
+TBD
+
+### New Features
+
+*   [[PR 622](https://github.com/datastax/csharp-driver/pull/622)] Fix some freezes caused by the application running slowly after a request execution
+
 ## 3.22.0
 
 2024-09-30

src/Cassandra.IntegrationTests/Core/SessionExecuteAsyncTests.cs

@@ -14,7 +14,9 @@
 //   limitations under the License.
 //
 using System;
+using System.Diagnostics;
 using System.Linq;
+using System.Threading;
 using System.Threading.Tasks;
 
 using NUnit.Framework;
@@ -23,6 +25,14 @@ namespace Cassandra.IntegrationTests.Core
 {
     public class SessionExecuteAsyncTests : SimulacronTest
     {
+        public override void OneTimeSetUp()
+        {
+            base.OneTimeSetUp();
+
+            const int minThreads = 32;
+            ThreadPool.SetMinThreads(minThreads, minThreads);
+        }
+
         [Test]
         public void SessionExecuteAsyncCQLQueryToSync()
         {
@@ -93,5 +103,30 @@ public void SessionExecuteAsyncCQLQueriesParallel()
             Assert.NotNull(task2.Result.First().GetValue<string>("key"));
             Assert.NotNull(task3.Result.First().GetValue<string[]>("tokens"));
         }
+
+        [Test]
+        public async Task SessionExecuteAsyncCQLQueriesParallelAndSlowResponseProcessingInUserThread()
+        {
+            const int sleepTimeMs = 3_000;
+            const int maxExpectedWaitingTimeMs = 5_000;
+            for (var i = 0; i < 3; i++)
+            {
+                var sw = Stopwatch.StartNew();
+
+                var tasks = Enumerable.Range(0, 10)
+                                      .Select(_ => Task.Run(async () =>
+                                      {
+                                          var statement = new SimpleStatement("SELECT * FROM system.local");
+                                          await Session.ExecuteAsync(statement).ConfigureAwait(false);
+                                          Thread.Sleep(sleepTimeMs);
+                                      }))
+                                      .ToArray();
+                await Task.WhenAll(tasks).ConfigureAwait(false);
+
+                sw.Stop();  
+
+                Assert.Less(sw.ElapsedMilliseconds, maxExpectedWaitingTimeMs);
+            }
+        }
     }
 }

src/Cassandra/Requests/TcsMetricsRequestResultHandler.cs

@@ -30,7 +30,11 @@ internal class TcsMetricsRequestResultHandler : IRequestResultHandler
         public TcsMetricsRequestResultHandler(IRequestObserver requestObserver)
         {
             _requestObserver = requestObserver;
+#if NET452
             _taskCompletionSource = new TaskCompletionSource<RowSet>();
+#else
+            _taskCompletionSource = new TaskCompletionSource<RowSet>(TaskCreationOptions.RunContinuationsAsynchronously);
+#endif
         }
 
         public async Task TrySetResultAsync(RowSet result, SessionRequestInfo sessionRequestInfo)