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