public

JohannesRudolph / MethodStatics.cs

Created 2011-06-26

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
 
namespace MethodStaticLocals
{
    class ExpensiveObject 
    {
        public ExpensiveObject()
        {
            Console.WriteLine( "Creating Expensive object" );
        }
    };
 
    class MainClass
    {
        public static void Main( string[] args )
        {
            Expression<Action> call = () => Func( "hello" );
 
            Invoke( call );
            Invoke( call );
        }
 
        // caches handles for expresisons, as they are expensive to find.
        static Dictionary<Expression, RuntimeMethodHandle> handleCache = new Dictionary<Expression, RuntimeMethodHandle>();
        // static locals are managed per method handle
        static Dictionary<RuntimeMethodHandle, Dictionary<string, object>> staticLocals = new Dictionary<RuntimeMethodHandle, Dictionary<string, object>>();
        // redirects are individual for each expression tree
        static Dictionary<Expression, Delegate> redirects = new Dictionary<Expression, Delegate>();
 
        static void Invoke( Expression<Action> call )
        {
            if (call.Parameters != null && call.Parameters.Any())
                throw new InvalidOperationException();
 
            if (call.Body.NodeType != ExpressionType.Call)
                throw new InvalidOperationException();
 
            Delegate redirectedInvocation = SetupRedirectedInvocation( call );
 
            redirectedInvocation.DynamicInvoke();
           
        }
 
        private static Delegate SetupRedirectedInvocation( Expression<Action> call )
        {
            Delegate redirectedInvocation;
            if (!redirects.TryGetValue( call, out redirectedInvocation ))
            {
                RuntimeMethodHandle caller = SetupCaller( call );
 
                Console.WriteLine( "Creating redirect for {0}", caller.Value );
                MethodCallExpression callExpression = (MethodCallExpression)call.Body;
 
                // add staticLocals dictionary as argument
                var arguments = callExpression.Arguments.ToList();
                arguments.Add( Expression.Constant( staticLocals[caller] ) );
 
                // todo: dynamically find redirect
                var redirect = MethodOf( () => Func( default( string ), default( Dictionary<string, object> ) ) );
 
                LambdaExpression redirectedExpression = Expression.Lambda( Expression.Call( callExpression.Object, redirect, arguments ), new ParameterExpression[0] );
 
                redirectedInvocation = redirectedExpression.Compile();
                redirects.Add( call, redirectedInvocation );
            }
            return redirectedInvocation;
        }
 
        private static RuntimeMethodHandle SetupCaller( Expression<Action> call )
        {
            RuntimeMethodHandle caller;
            if (!handleCache.TryGetValue( call, out caller ))
            {
                caller = new StackFrame( 1 ).GetMethod().MethodHandle;
                handleCache.Add( call, caller );
                staticLocals.Add( caller, new Dictionary<string, object>() );
            }
            return caller;
        }
 
        public static MethodInfo MethodOf( Expression<Action> expression )
        {
            MethodCallExpression body = (MethodCallExpression)expression.Body;
            return body.Method;
        }
 
        [Obsolete( "do not call directly" )]
        public static void Func( string arg )
        {
        }
 
        private static void Func( string arg, Dictionary<string, object> staticLocals )
        {
            if (!staticLocals.ContainsKey( "expensive"))
            {
                staticLocals.Add( "expensive", new ExpensiveObject() );
            }
 
            ExpensiveObject obj = (ExpensiveObject)staticLocals["expensive"];
            Console.WriteLine( "Func invoked: arg: {0}; expensive: {1}", arg, obj );
        }
    }
}