CSHARP-724. Unset primary flag when instance disconnects or a new primary is elected

Author: Sridhar Nanjundeswaran

MongoDB.Driver/Communication/MongoServerInstance.cs

@@ -530,6 +530,29 @@ internal void SetState(MongoServerState state)
             OnStateChanged();
         }
 
+        /// <summary>
+        /// Unset the primary flag on this instance but retain all other information
+        /// </summary>
+        internal void UnsetPrimary()
+        {
+            lock (_serverInstanceLock)
+            {
+                _serverInfo.IsPrimary = false;
+            }
+        }
+
+        /// <summary>
+        /// Unset the primary flag on this instance but retain all other information
+        /// </summary>
+        internal void UnsetPrimarySecondary()
+        {
+            lock (_serverInstanceLock)
+            {
+                _serverInfo.IsPrimary = false;
+                _serverInfo.IsSecondary = false;
+            }
+        }
+
         // private methods
         private void LookupServerInformation(MongoConnection connection)
         {
@@ -659,6 +682,7 @@ private void Ping(MongoConnection connection)
             catch
             {
                 _pingTimeAggregator.Clear();
+                UnsetPrimarySecondary();
                 SetState(MongoServerState.Disconnected);
                 throw;
             }

MongoDB.Driver/Communication/Proxies/ReplicaSetMongoServerProxy.cs

@@ -254,6 +254,14 @@ private void ProcessConnectedPrimaryStateChange(MongoServerInstance instance)
                 // remove instances the primary doesn't know about and add instances we don't know about
                 MakeInstancesMatchAddresses(members);
             }
+            var instancesMarkedPrimary = Instances.Where(x => x.IsPrimary);
+            foreach (var otherInstance in instancesMarkedPrimary)
+            {
+                if (!otherInstance.Address.Equals(instance.Address))
+                {
+                    otherInstance.UnsetPrimary();
+                }
+            }
         }
 
         private void ProcessConnectedSecondaryStateChange(MongoServerInstance instance)