Clearing pools via delegates

Author: bahusoid

src/NHibernate/Driver/ReflectionBasedDriver.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Data.Common;
+using System.Linq.Expressions;
 using System.Reflection;
 using NHibernate.Util;
 
@@ -86,18 +87,18 @@ protected static class PoolHelper<T> where T : IDriver
 		{
 			// Static field in generic class => one field per concrete type used. This is exactly what
 			// we need here, do not move the generic argument to the method. Otherwise it will cache the
-			// method info of the first driver type used, and reuse it for other driver types, which
+			// delegate of the first driver type used, and reuse it for other driver types, which
 			// would fail.
-			private static volatile MethodInfo _clearPool;
-			private static volatile MethodInfo _clearAllPools;
+			private static volatile System.Action<DbConnection> _clearPool;
+			private static volatile System.Action _clearAllPools;
 
 			/// <summary>
 			/// Clears the connection pool.
 			/// </summary>
 			/// <param name="driver">The driver for which the connection pool has to be cleared.</param>
 			/// <param name="connectionString">The connection string of connections for which to clear the pool.
 			/// <c>null</c> for clearing them all.</param>
-			internal static void ClearPool(T driver, string connectionString)
+			public static void ClearPool(T driver, string connectionString)
 			{
 				// In case of concurrent threads, may initialize many times. We do not care.
 				// Members are volatile for avoiding they get used while their constructor is not yet ended.
@@ -106,8 +107,14 @@ internal static void ClearPool(T driver, string connectionString)
 					using (var clearConnection = driver.CreateConnection())
 					{
 						var connectionType = clearConnection.GetType();
-						_clearPool = connectionType.GetMethod("ClearPool") ?? throw new InvalidOperationException("Unable to resolve ClearPool method.");
-						_clearAllPools = connectionType.GetMethod("ClearAllPools") ?? throw new InvalidOperationException("Unable to resolve ClearAllPools method.");
+
+						var clearPoolMethodInfo = GetMethod(connectionType, "ClearPool");
+						var parameter = Expression.Parameter(typeof(DbConnection));
+						var methodCall = Expression.Call(clearPoolMethodInfo, Expression.Convert(parameter, connectionType));
+						_clearPool = Expression.Lambda<Action<DbConnection>>(methodCall, parameter).Compile();
+
+						var clearAllPoolsMethodInfo = GetMethod(connectionType, "ClearAllPools");
+						_clearAllPools = (System.Action) Delegate.CreateDelegate(typeof(System.Action), clearAllPoolsMethodInfo);
 					}
 				}
 
@@ -116,12 +123,17 @@ internal static void ClearPool(T driver, string connectionString)
 					using (var clearConnection = driver.CreateConnection())
 					{
 						clearConnection.ConnectionString = connectionString;
-						_clearPool.Invoke(null, new object[] {clearConnection});
+						_clearPool(clearConnection);
 					}
 					return;
 				}
 
-				_clearAllPools.Invoke(null, Array.Empty<object>());
+				_clearAllPools();
+			}
+
+			private static MethodInfo GetMethod(System.Type type, string methodName)
+			{
+				return type.GetMethod(methodName) ?? throw new InvalidOperationException($"Unable to resolve {type.Name}.{methodName} method.");
 			}
 		}
 	}