Fix GetQueryCache building two different caches for same region.

Author: fredericDelaporte

src/NHibernate/Async/Impl/SessionFactoryImpl.cs

@@ -86,9 +86,9 @@ public sealed partial class SessionFactoryImpl : ISessionFactoryImplementor, IOb
 			{
 				queryCache.Destroy();
 
-				foreach (IQueryCache cache in queryCaches.Values)
+				foreach (var cache in queryCaches.Values)
 				{
-					cache.Destroy();
+					cache.Value.Destroy();
 				}
 
 				updateTimestampsCache.Destroy();
@@ -296,10 +296,9 @@ public sealed partial class SessionFactoryImpl : ISessionFactoryImplementor, IOb
 				{
 					if (settings.IsQueryCacheEnabled)
 					{
-						IQueryCache currentQueryCache;
-						if (queryCaches.TryGetValue(cacheRegion, out currentQueryCache))
+						if (queryCaches.TryGetValue(cacheRegion, out var currentQueryCache))
 						{
-							return currentQueryCache.ClearAsync(cancellationToken);
+							return currentQueryCache.Value.ClearAsync(cancellationToken);
 						}
 					}
 				}

src/NHibernate/Impl/SessionFactoryImpl.cs

@@ -148,7 +148,7 @@ public void HandleEntityNotFound(string entityName, object id)
 		private readonly IQueryCache queryCache;
 
 		[NonSerialized]
-		private readonly ConcurrentDictionary<string, IQueryCache> queryCaches;
+		private readonly ConcurrentDictionary<string, Lazy<IQueryCache>> queryCaches;
 		[NonSerialized]
 		private readonly SchemaExport schemaExport;
 		[NonSerialized]
@@ -379,7 +379,7 @@ public SessionFactoryImpl(Configuration cfg, IMapping mapping, Settings settings
 			{
 				updateTimestampsCache = new UpdateTimestampsCache(settings, properties);
 				queryCache = settings.QueryCacheFactory.GetQueryCache(null, updateTimestampsCache, settings, properties);
-				queryCaches = new ConcurrentDictionary<string, IQueryCache>();
+				queryCaches = new ConcurrentDictionary<string, Lazy<IQueryCache>>();
 			}
 			else
 			{
@@ -845,9 +845,9 @@ public void Close()
 			{
 				queryCache.Destroy();
 
-				foreach (IQueryCache cache in queryCaches.Values)
+				foreach (var cache in queryCaches.Values)
 				{
-					cache.Destroy();
+					cache.Value.Destroy();
 				}
 
 				updateTimestampsCache.Destroy();
@@ -1027,21 +1027,18 @@ public IQueryCache GetQueryCache(string cacheRegion)
 				return null;
 			}
 
-			var wasAdded = false;
 			// The factory may be run concurrently by threads trying to get the same region.
-			// But the GetOrAdd will yield the same cache for all threads, so in case of add, use
-			// it to update allCacheRegions
-			var cache = queryCaches.GetOrAdd(
+			// But the GetOrAdd will yield the same lazy for all threads, so only one will
+			// initialize. https://stackoverflow.com/a/31637510/1178314
+			return queryCaches.GetOrAdd(
 				cacheRegion,
-				cr =>
-				{
-					var currentQueryCache = settings.QueryCacheFactory.GetQueryCache(cacheRegion, updateTimestampsCache, settings, properties);
-					wasAdded = true;
-					return currentQueryCache;
-				});
-			if (wasAdded)
-				allCacheRegions[cache.RegionName] = cache.Cache;
-			return cache;
+				cr => new Lazy<IQueryCache>(
+					() =>
+					{
+						var currentQueryCache = settings.QueryCacheFactory.GetQueryCache(cr, updateTimestampsCache, settings, properties);
+						allCacheRegions[currentQueryCache.RegionName] = currentQueryCache.Cache;
+						return currentQueryCache;
+					})).Value;
 		}
 
 		public void EvictQueries()
@@ -1067,10 +1064,9 @@ public void EvictQueries(string cacheRegion)
 			{
 				if (settings.IsQueryCacheEnabled)
 				{
-					IQueryCache currentQueryCache;
-					if (queryCaches.TryGetValue(cacheRegion, out currentQueryCache))
+					if (queryCaches.TryGetValue(cacheRegion, out var currentQueryCache))
 					{
-						currentQueryCache.Clear();
+						currentQueryCache.Value.Clear();
 					}
 				}
 			}