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：

+ View Code?

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35

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：

+ View Code?

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

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