Make SessionFactoryImpl.collectionPersisters a ReadOnlyDictionary to line up with how collectionMetadata is built and improve determistic behavior under accidental multithreading

Author: mjkent

src/NHibernate/Impl/SessionFactoryImpl.cs

@@ -110,7 +110,7 @@ public void HandleEntityNotFound(string entityName, string propertyName, object
 		[NonSerialized]
 		private readonly IDictionary<string, ICollectionMetadata> collectionMetadata;
 		[NonSerialized]
-		private readonly Dictionary<string, ICollectionPersister> collectionPersisters;
+		private readonly IDictionary<string, ICollectionPersister> collectionPersisters;
 		[NonSerialized]
 		private readonly ILookup<string, ICollectionPersister> collectionPersistersSpaces;
 
@@ -296,7 +296,7 @@ public SessionFactoryImpl(Configuration cfg, IMapping mapping, Settings settings
 			classMetadata = new ReadOnlyDictionary<string, IClassMetadata>(classMeta);
 
 			Dictionary<string, ISet<string>> tmpEntityToCollectionRoleMap = new Dictionary<string, ISet<string>>();
-			collectionPersisters = new Dictionary<string, ICollectionPersister>();
+			var collPersisters = new Dictionary<string, ICollectionPersister>();
 			foreach (Mapping.Collection model in cfg.CollectionMappings)
 			{
 				var cache = GetCacheConcurrencyStrategy(
@@ -306,7 +306,7 @@ public SessionFactoryImpl(Configuration cfg, IMapping mapping, Settings settings
 					model.OwnerEntityName,
 					caches);
 				var persister = PersisterFactory.CreateCollectionPersister(model, cache, this);
-				collectionPersisters[model.Role] = persister;
+				collPersisters[model.Role] = persister;
 				IType indexType = persister.IndexType;
 				if (indexType != null && indexType.IsAssociationType && !indexType.IsAnyType)
 				{
@@ -333,6 +333,8 @@ public SessionFactoryImpl(Configuration cfg, IMapping mapping, Settings settings
 				}
 			}
 
+			collectionPersisters = new ReadOnlyDictionary<string, ICollectionPersister>(collPersisters);
+
 			collectionPersistersSpaces = collectionPersisters
 				.SelectMany(x => x.Value.CollectionSpaces.Select(y => new { QuerySpace = y, Persister = x.Value }))
 				.ToLookup(x => x.QuerySpace, x => x.Persister);