CSHARP-3182: Getting timeout error when using driver in WinForms .net core 3.1 project.

Author: DmitryLukyanov

src/MongoDB.Driver.Core/Core/Servers/RoundTripTimeMonitor.cs

@@ -84,8 +84,6 @@ public void Dispose()
 
         public async Task RunAsync()
         {
-            await Task.Yield(); // return control immediately
-
             while (!_cancellationToken.IsCancellationRequested)
             {
                 try

src/MongoDB.Driver.Core/Core/Servers/ServerMonitor.cs

@@ -128,7 +128,14 @@ public void Initialize()
         {
             if (_state.TryChange(State.Initial, State.Open))
             {
-                _ = MonitorServerAsync().ConfigureAwait(false);
+                // the call to Task.Factory.StartNew is not normally recommended or necessary
+                // we are using it temporarily to work around a race condition in some of our tests
+                // the issue is that we set up some mocked async methods to return results immediately synchronously
+                // which results in the MonitorServerAsync method making more progress synchronously than the test expected
+                // by using Task.Factory.StartNew we introduce a short delay before the MonitorServerAsync Task starts executing
+                // the delay is whatever time it takes for the new Task to be activated and scheduled
+                // and the delay is usually long enough for the test to get past the race condition (though not guaranteed)
+                _ = Task.Factory.StartNew(() => _ = MonitorServerAsync().ConfigureAwait(false)).ConfigureAwait(false);
                 _ = _roundTripTimeMonitor.RunAsync().ConfigureAwait(false);
             }
         }
@@ -189,8 +196,6 @@ private async Task<IConnection> InitializeConnectionAsync(CancellationToken canc
 
         private async Task MonitorServerAsync()
         {
-            await Task.Yield(); // return control immediately
-
             var metronome = new Metronome(_serverMonitorSettings.HeartbeatInterval);
             var monitorCancellationToken = _monitorCancellationTokenSource.Token;
 

tests/MongoDB.Driver.Core.Tests/Core/Servers/HeartbeatDelayTests.cs

@@ -14,6 +14,7 @@
 */
 
 using System;
+using System.Diagnostics;
 using System.Threading;
 using System.Threading.Tasks;
 using FluentAssertions;
@@ -38,13 +39,20 @@ public void Dispose_can_be_called_multiple_times()
         public void RequestHeartbeat_should_respect_to_minHeartbeatInterval([Values(10, -1)]int heartbeatIntervalInMinutes)
         {
             var heartbeatInterval = heartbeatIntervalInMinutes == -1 ? Timeout.InfiniteTimeSpan : TimeSpan.FromMinutes(heartbeatIntervalInMinutes);
-            var subject = new HeartbeatDelay(heartbeatInterval, TimeSpan.FromSeconds(2));
+            var minHeartbeatInterval = TimeSpan.FromSeconds(2);
 
+            var stopwatch = Stopwatch.StartNew();
+            var subject = new HeartbeatDelay(heartbeatInterval, minHeartbeatInterval);
             subject.RequestHeartbeat();
+            var timeout = TimeSpan.FromMinutes(1);
+            var result = Task.WaitAny(subject.Task, Task.Delay(timeout));
+            if (result != 0)
+            {
+                throw new Exception($"The test timeout {timeout} is exceeded.");
+            }
+            stopwatch.Stop();
 
-            SpinWait.SpinUntil(() => subject.Task.Status != TaskStatus.WaitingForActivation, TimeSpan.FromMilliseconds(1500)).Should().BeFalse();
-            Thread.Sleep(TimeSpan.FromMilliseconds(700));
-            subject.Task.Status.Should().Be(TaskStatus.RanToCompletion);
+            stopwatch.Elapsed.Should().BeGreaterOrEqualTo(minHeartbeatInterval - TimeSpan.FromMilliseconds(15));
         }
 
         [Fact]