C# Expression 表达式树 缓存

在学习mvc3源代码的时候，发现里面调用action的源代码如下：

 private static ActionExecutor GetExecutor(MethodInfo methodInfo) {            // Parameters to executor            ParameterExpression controllerParameter = Expression.Parameter(typeof(ControllerBase), "controller");            ParameterExpression parametersParameter = Expression.Parameter(typeof(object[]), "parameters");            // Build parameter list            List<Expression> parameters = new List<Expression>();            ParameterInfo[] paramInfos = methodInfo.GetParameters();            for (int i = 0; i < paramInfos.Length; i++) {                ParameterInfo paramInfo = paramInfos[i];                BinaryExpression valueObj = Expression.ArrayIndex(parametersParameter, Expression.Constant(i));                UnaryExpression valueCast = Expression.Convert(valueObj, paramInfo.ParameterType);                // valueCast is "(Ti) parameters[i]"                parameters.Add(valueCast);            }            // Call method            UnaryExpression instanceCast = (!methodInfo.IsStatic) ? Expression.Convert(controllerParameter, methodInfo.ReflectedType) : null;            MethodCallExpression methodCall = methodCall = Expression.Call(instanceCast, methodInfo, parameters);            // methodCall is "((TController) controller) method((T0) parameters[0], (T1) parameters[1], ...)"            // Create function            if (methodCall.Type == typeof(void)) {                Expression<VoidActionExecutor> lambda = Expression.Lambda<VoidActionExecutor>(methodCall, controllerParameter, parametersParameter);                VoidActionExecutor voidExecutor = lambda.Compile();                return WrapVoidAction(voidExecutor);            }            else {                // must coerce methodCall to match ActionExecutor signature                UnaryExpression castMethodCall = Expression.Convert(methodCall, typeof(object));                Expression<ActionExecutor> lambda = Expression.Lambda<ActionExecutor>(castMethodCall, controllerParameter, parametersParameter);                return lambda.Compile();            }        }

里面用了表达式树，当时的我对表达式树还不怎么了解，曾提出一个疑问，为什么不用反射而要用表达式树了，在网上找了很多资料说明表达式树比反射性能要高。甚至根由大牛曾提出表达式缓存的思想，http://blog.zhaojie.me/2009/03/expression-cache-2-simple-key-cache.html。然而在mvc3中有些地方还是用了表达式树缓存的（CachedExpressionCompiler mvc3自带的）

至于怎么缓存我这里就不班门弄斧了，只是告诉一下大家Compile()这个东东很伤性能啊。

现在说说我的测试吧：

 static void Main(string[] args)        {            TestExpress(100000);            TestExpress(500000);            Console.ReadLine();        }        private static void TestExpress(int count)        {            // int count = 100000;            Console.WriteLine("循环次数：" + count);            Expression<Func<int, int, int>> addExpr = (x, y) => x + y;            var start = DateTime.Now;            for (int i = 0; i < count; i++)            {                Func<int, int, int> test = addExpr.Compile();                int result = test(1, 2);            }            var end = DateTime.Now;            var time = end - start;            Console.WriteLine("no Cache:" + time.Milliseconds);            Func<int, int, int> addResult = addExpr.Compile();            start = DateTime.Now;            for (int i = 0; i < count; i++)            {                int result = addResult(1, 2);            }            end = DateTime.Now;            time = end - start;            Console.WriteLine("Cache:" + time.Milliseconds);        }

我在release下得到的结果：

在每个计算机每次执行的结果都是不同的，但是缓存了时间明显要短。

我把有关Expression表达式树缓存 Expression表达式树序列化的源代码整理了一下，方便大家下载。http://download.csdn.net/detail/dz45693/4375232