CSHARP-574: refactor so callers of GetMatchingInstances decide which instances should be matched against.

Author: rstam

Driver/Internal/ConnectedInstanceCollection.cs

@@ -57,10 +57,10 @@ public void Clear()
         }
 
         /// <summary>
-        /// Gets a list of InstanceWithPingTimes.
+        /// Gets a list of all instances.
         /// </summary>
-        /// <returns>The list of InstanceWithPingTimes</returns>
-        public List<InstanceWithPingTime> GetInstancesWithPingTime()
+        /// <returns>The list of all instances.</returns>
+        public List<InstanceWithPingTime> GetAllInstances()
         {
             lock (_connectedInstancesLock)
             {
@@ -83,6 +83,38 @@ public MongoServerInstance GetPrimary()
             }
         }
 
+        /// <summary>
+        /// Gets a list of primary and secondary instances.
+        /// </summary>
+        /// <returns>The list of primary and secondary instances.</returns>
+        public List<InstanceWithPingTime> GetPrimaryAndSecondaries()
+        {
+            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)
+                    .Select(x => new InstanceWithPingTime { Instance = x.Instance, CachedAveragePingTime = x.CachedAveragePingTime })
+                    .ToList();
+            }
+        }
+
+        /// <summary>
+        /// Gets a list of secondaries.
+        /// </summary>
+        /// <returns>The list of secondaries.</returns>
+        public List<InstanceWithPingTime> GetSecondaries()
+        {
+            lock (_connectedInstancesLock)
+            {
+                // note: make copies of InstanceWithPingTime values because they can change after we return
+                return _instances
+                    .Where(x => x.Instance.IsSecondary)
+                    .Select(x => new InstanceWithPingTime { Instance = x.Instance, CachedAveragePingTime = x.CachedAveragePingTime })
+                    .ToList();
+            }
+        }
+
         /// <summary>
         /// Ensures that the instance is in the collection.
         /// </summary>

Driver/Internal/ReplicaSetMongoServerProxy.cs

@@ -87,14 +87,14 @@ protected override MongoServerInstance ChooseServerInstance(ConnectedInstanceCol
                     }
                     else
                     {
-                        return GetMatchingInstance(connectedInstances, readPreference, secondaryAcceptableLatency);
+                        return GetMatchingInstance(connectedInstances.GetSecondaries(), readPreference, secondaryAcceptableLatency);
                     }
 
                 case ReadPreferenceMode.Secondary:
-                    return GetMatchingInstance(connectedInstances, readPreference, secondaryAcceptableLatency);
+                    return GetMatchingInstance(connectedInstances.GetSecondaries(), readPreference, secondaryAcceptableLatency);
 
                 case ReadPreferenceMode.SecondaryPreferred:
-                    var secondary = GetMatchingInstance(connectedInstances, readPreference, secondaryAcceptableLatency);
+                    var secondary = GetMatchingInstance(connectedInstances.GetSecondaries(), readPreference, secondaryAcceptableLatency);
                     if (secondary != null)
                     {
                         return secondary;
@@ -105,7 +105,7 @@ protected override MongoServerInstance ChooseServerInstance(ConnectedInstanceCol
                     }
 
                 case ReadPreferenceMode.Nearest:
-                    return GetMatchingInstance(connectedInstances, readPreference, secondaryAcceptableLatency);
+                    return GetMatchingInstance(connectedInstances.GetPrimaryAndSecondaries(), readPreference, secondaryAcceptableLatency);
 
                 default:
                     throw new MongoInternalException("Invalid ReadPreferenceMode.");
@@ -203,13 +203,12 @@ protected override void ProcessConnectedInstanceStateChange(MongoServerInstance
         /// <summary>
         /// Gets a randomly selected matching instance.
         /// </summary>
+        /// <param name="instancesWithPingTime">A list of instances from which to find a matching instance.</param>
         /// <param name="readPreference">The read preference that must be matched.</param>
         /// <param name="secondaryAcceptableLatency">The maximum acceptable secondary latency.</param>
         /// <returns>A randomly selected matching instance.</returns>
-        public MongoServerInstance GetMatchingInstance(ConnectedInstanceCollection connectedInstances, ReadPreference readPreference, TimeSpan secondaryAcceptableLatency)
+        public MongoServerInstance GetMatchingInstance(List<ConnectedInstanceCollection.InstanceWithPingTime> instancesWithPingTime, ReadPreference readPreference, TimeSpan secondaryAcceptableLatency)
         {
-            var instancesWithPingTime = connectedInstances.GetInstancesWithPingTime();
-
             var tagSets = readPreference.TagSets ?? new ReplicaSetTagSet[] { new ReplicaSetTagSet() };
             foreach (var tagSet in tagSets)
             {
@@ -224,15 +223,12 @@ public MongoServerInstance GetMatchingInstance(ConnectedInstanceCollection conne
                     }
 
                     var instance = instanceWithPingTime.Instance;
-                    if (instance.IsSecondary || (readPreference.ReadPreferenceMode == ReadPreferenceMode.Nearest && instance.IsPrimary))
+                    if (tagSet.MatchesInstance(instance))
                     {
-                        if (tagSet.MatchesInstance(instance))
+                        matchingInstances.Add(instance);
+                        if (maxPingTime == TimeSpan.MaxValue)
                         {
-                            matchingInstances.Add(instance);
-                            if (maxPingTime == TimeSpan.MaxValue)
-                            {
-                                maxPingTime = instanceWithPingTime.CachedAveragePingTime + secondaryAcceptableLatency;
-                            }
+                            maxPingTime = instanceWithPingTime.CachedAveragePingTime + secondaryAcceptableLatency;
                         }
                     }
                 }

Driver/Internal/ShardedMongoServerProxy.cs

@@ -59,7 +59,7 @@ public ShardedMongoServerProxy(MongoServer server, IEnumerable<MongoServerInstan
         /// <returns>A MongoServerInstance.</returns>
         protected override MongoServerInstance ChooseServerInstance(ConnectedInstanceCollection connectedInstances, ReadPreference readPreference)
         {
-            var instancesWithPingTime = connectedInstances.GetInstancesWithPingTime();
+            var instancesWithPingTime = connectedInstances.GetAllInstances();
             if (instancesWithPingTime.Count == 0)
             {
                 return null;