Replace an O(n) lookup in LINQ query parsing by an O(1) one

src/NHibernate.Test/Async/Hql/HQLFunctions.cs

@@ -1079,9 +1079,9 @@ public async Task Current_DateAsync()
 		public async Task Current_Date_IsLowestTimeOfDayAsync()
 		{
 			AssumeFunctionSupported("current_date");
-			var now = DateTime.Now;
 			if (!TestDialect.SupportsNonDataBoundCondition)
 				Assert.Ignore("Test is not supported by the target database");
+			var now = DateTime.Now;
 			if (now.TimeOfDay < TimeSpan.FromMinutes(5) || now.TimeOfDay > TimeSpan.Parse("23:55"))
 				Assert.Ignore("Test is unreliable around midnight");
 

src/NHibernate/Linq/Functions/DefaultLinqToHqlGeneratorsRegistry.cs

@@ -1,4 +1,5 @@
-using System.Collections.Generic;
+using System.Collections.Concurrent;
+using System.Collections.Generic;
 using System.Linq;
 using System.Reflection;
 
@@ -10,6 +11,9 @@ public class DefaultLinqToHqlGeneratorsRegistry : ILinqToHqlGeneratorsRegistry
 		private readonly Dictionary<MemberInfo, IHqlGeneratorForProperty> registeredProperties = new Dictionary<MemberInfo, IHqlGeneratorForProperty>();
 		private readonly List<IRuntimeMethodHqlGenerator> runtimeMethodHqlGenerators = new List<IRuntimeMethodHqlGenerator>();
 
+		private readonly ConcurrentDictionary<MethodInfo, IHqlGeneratorForMethod> _cachedRuntimeMethodHqlGenerators =
+			new ConcurrentDictionary<MethodInfo, IHqlGeneratorForMethod>();
+
 		public DefaultLinqToHqlGeneratorsRegistry()
 		{
 			RegisterGenerator(new StandardLinqExtensionMethodGenerator());
@@ -69,14 +73,15 @@ public DefaultLinqToHqlGeneratorsRegistry()
 
 		protected bool GetRuntimeMethodGenerator(MethodInfo method, out IHqlGeneratorForMethod methodGenerator)
 		{
-			methodGenerator = null;
-
-			foreach (var typeGenerator in runtimeMethodHqlGenerators.Where(typeGenerator => typeGenerator.SupportsMethod(method)))
-			{
-				methodGenerator = typeGenerator.GetMethodGenerator(method);
-				return true;
-			}
-			return false;
+			methodGenerator = _cachedRuntimeMethodHqlGenerators.GetOrAdd(
+				method,
+				m =>
+					runtimeMethodHqlGenerators
+						.Where(g => g.SupportsMethod(m))
+						.Select(g => g.GetMethodGenerator(m))
+						.FirstOrDefault());
+
+			return methodGenerator != null;
 		}
 
 		public virtual bool TryGetGenerator(MethodInfo method, out IHqlGeneratorForMethod generator)
@@ -112,6 +117,7 @@ public virtual void RegisterGenerator(MemberInfo property, IHqlGeneratorForPrope
 		public void RegisterGenerator(IRuntimeMethodHqlGenerator generator)
 		{
 			runtimeMethodHqlGenerators.Add(generator);
+			_cachedRuntimeMethodHqlGenerators.Clear();
 		}
 	}
 }