CSHARP-724: Now that we have more robust primary tracking use that information in more places. Also, reset state verification timer on old primary whenever we discover a new primary so that the new state of the old primary will be determined as soon as possible.

Author: rstam

MongoDB.Driver/Communication/MongoServerInstance.cs

@@ -538,6 +538,7 @@ internal void UnsetPrimary()
             lock (_serverInstanceLock)
             {
                 _serverInfo.IsPrimary = false;
+                _stateVerificationTimer.Change(TimeSpan.Zero, TimeSpan.FromSeconds(10)); // verify state as soon as possible
             }
         }
 

MongoDB.Driver/Communication/Proxies/ConnectedInstanceCollection.cs

@@ -68,29 +68,18 @@ public List<InstanceWithPingTime> GetAllInstances()
             }
         }
 
-        /// <summary>
-        /// Gets the primary instance.
-        /// </summary>
-        /// <returns>The primary instance (or null if there is none).</returns>
-        public MongoServerInstance GetPrimary()
-        {
-            lock (_connectedInstancesLock)
-            {
-                return _instances.Select(x => x.Instance).FirstOrDefault(i => i.IsPrimary);
-            }
-        }
-
         /// <summary>
         /// Gets a list of primary and secondary instances.
         /// </summary>
+        /// <param name="primary">The current primary.</param>
         /// <returns>The list of primary and secondary instances.</returns>
-        public List<InstanceWithPingTime> GetPrimaryAndSecondaries()
+        public List<InstanceWithPingTime> GetPrimaryAndSecondaries(MongoServerInstance primary)
         {
             lock (_connectedInstancesLock)
             {
                 // note: make copies of InstanceWithPingTime values because they can change after we return
                 return _instances
-                    .Where(x => x.Instance.IsPrimary || x.Instance.IsSecondary)
+                    .Where(x => x.Instance == primary || x.Instance.IsSecondary)
                     .Select(x => new InstanceWithPingTime { Instance = x.Instance, CachedAveragePingTime = x.CachedAveragePingTime })
                     .ToList();
             }

MongoDB.Driver/Communication/Proxies/ReplicaSetMongoServerProxy.cs

@@ -96,13 +96,12 @@ protected override MongoServerInstance ChooseServerInstance(ConnectedInstanceCol
             switch (readPreference.ReadPreferenceMode)
             {
                 case ReadPreferenceMode.Primary:
-                    return connectedInstances.GetPrimary();
+                    return _primary;
 
                 case ReadPreferenceMode.PrimaryPreferred:
-                    var primary = connectedInstances.GetPrimary();
-                    if (primary != null)
+                    if (_primary != null)
                     {
-                        return primary;
+                        return _primary;
                     }
                     else
                     {
@@ -120,11 +119,11 @@ protected override MongoServerInstance ChooseServerInstance(ConnectedInstanceCol
                     }
                     else
                     {
-                        return connectedInstances.GetPrimary();
+                        return _primary;
                     }
 
                 case ReadPreferenceMode.Nearest:
-                    return GetMatchingInstance(connectedInstances.GetPrimaryAndSecondaries(), readPreference, secondaryAcceptableLatency);
+                    return GetMatchingInstance(connectedInstances.GetPrimaryAndSecondaries(_primary), readPreference, secondaryAcceptableLatency);
 
                 default:
                     throw new MongoInternalException("Invalid ReadPreferenceMode.");