CSHARP-3761: Fix issue with ObjectDisposedException. (#729)

CSHARP-3761: Fix issue with ObjectDisposedException.

Author: DmitryLukyanov

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

@@ -76,7 +76,7 @@ public void RequestHeartbeat()
 
         public void Wait(CancellationToken cancellationToken)
         {
-            _taskCompletionSource.Task.Wait();
+            _taskCompletionSource.Task.Wait(cancellationToken);
         }
 
         private void TimerCallback(object state)

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

@@ -14,7 +14,6 @@
 */
 
 using System;
-using System.Collections.Concurrent;
 using System.Diagnostics;
 using System.Net;
 using System.Threading;
@@ -36,6 +35,7 @@ internal sealed class ServerMonitor : IServerMonitor
         private readonly EndPoint _endPoint;
         private HeartbeatDelay _heartbeatDelay;
         private readonly object _lock = new object();
+        private readonly CancellationToken _monitorCancellationToken; // used to cancel the entire monitor
         private readonly CancellationTokenSource _monitorCancellationTokenSource; // used to cancel the entire monitor
         private readonly IRoundTripTimeMonitor _roundTripTimeMonitor;
         private readonly ServerApi _serverApi;
@@ -101,7 +101,8 @@ public ServerMonitor(
             eventSubscriber.TryGetEventHandler(out _sdamInformationEventHandler);
             _serverApi = serverApi;
 
-            _heartbeatCancellationTokenSource = CancellationTokenSource.CreateLinkedTokenSource(_monitorCancellationTokenSource.Token);
+            _monitorCancellationToken = _monitorCancellationTokenSource.Token;
+            _heartbeatCancellationTokenSource = CancellationTokenSource.CreateLinkedTokenSource(_monitorCancellationToken);
         }
 
         public ServerDescription Description => Interlocked.CompareExchange(ref _currentDescription, null, null);
@@ -118,7 +119,7 @@ public void CancelCurrentCheck()
                 {
                     _heartbeatCancellationTokenSource.Cancel();
                     _heartbeatCancellationTokenSource.Dispose();
-                    _heartbeatCancellationTokenSource = CancellationTokenSource.CreateLinkedTokenSource(_monitorCancellationTokenSource.Token);
+                    _heartbeatCancellationTokenSource = CancellationTokenSource.CreateLinkedTokenSource(_monitorCancellationToken);
                     // the previous hello or legacy hello cancellation token is still cancelled
 
                     toDispose = _connection;
@@ -147,20 +148,13 @@ public void Initialize()
             if (_state.TryChange(State.Initial, State.Open))
             {
                 _roundTripTimeMonitor.Start();
-                _serverMonitorThread = new Thread(ThreadStart) { IsBackground = true };
-                _serverMonitorThread.Start();
+                _serverMonitorThread = new Thread(new ParameterizedThreadStart(ThreadStart)) { IsBackground = true };
+                _serverMonitorThread.Start(_monitorCancellationToken);
             }
 
-            void ThreadStart()
+            void ThreadStart(object monitorCancellationToken)
             {
-                try
-                {
-                    MonitorServer();
-                }
-                catch (OperationCanceledException)
-                {
-                    // ignore OperationCanceledException
-                }
+                MonitorServer((CancellationToken)monitorCancellationToken);
             }
         }
 
@@ -218,10 +212,9 @@ private IConnection InitializeConnection(CancellationToken cancellationToken) //
             return connection;
         }
 
-        private void MonitorServer()
+        private void MonitorServer(CancellationToken monitorCancellationToken)
         {
             var metronome = new Metronome(_serverMonitorSettings.HeartbeatInterval);
-            var monitorCancellationToken = _monitorCancellationTokenSource.Token;
 
             while (!monitorCancellationToken.IsCancellationRequested)
             {