openhardwaremonitor/Hardware/PInvokeDelegateFactory.cs

/*
 
  This Source Code Form is subject to the terms of the Mozilla Public
  License, v. 2.0. If a copy of the MPL was not distributed with this
  file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
  Copyright (C) 2009-2012 Michael M<EFBFBD>ller <mmoeller@openhardwaremonitor.org>
	
*/

using System;
using System.Collections.Generic;
using System.Reflection;
using System.Reflection.Emit;
using System.Runtime.InteropServices;
using OpenHardwareMonitor.Collections;

namespace OpenHardwareMonitor.Hardware {

  internal static class PInvokeDelegateFactory {

    private static readonly ModuleBuilder moduleBuilder = 
      AppDomain.CurrentDomain.DefineDynamicAssembly(
        new AssemblyName("PInvokeDelegateFactoryInternalAssembly"),
        AssemblyBuilderAccess.Run).DefineDynamicModule(
        "PInvokeDelegateFactoryInternalModule");

    private static readonly IDictionary<Pair<DllImportAttribute, Type>, Type> wrapperTypes =
      new Dictionary<Pair<DllImportAttribute, Type>, Type>();

    public static void CreateDelegate<T>(DllImportAttribute dllImportAttribute,
      out T newDelegate, DllImportSearchPath dllImportSearchPath =
      DllImportSearchPath.System32) where T : class 
    {
      Type wrapperType;
      Pair<DllImportAttribute, Type> key =
        new Pair<DllImportAttribute, Type>(dllImportAttribute, typeof(T));
      wrapperTypes.TryGetValue(key, out wrapperType);

      if (wrapperType == null) {
        wrapperType = CreateWrapperType(typeof(T), dllImportAttribute, dllImportSearchPath);
        wrapperTypes.Add(key, wrapperType);
      }

      newDelegate = Delegate.CreateDelegate(typeof(T), wrapperType,
        dllImportAttribute.EntryPoint) as T;
    }

    private static Type CreateWrapperType(Type delegateType,
      DllImportAttribute dllImportAttribute,
      DllImportSearchPath dllImportSearchPath)
    {

      TypeBuilder typeBuilder = moduleBuilder.DefineType(
        "PInvokeDelegateFactoryInternalWrapperType" + wrapperTypes.Count);

      MethodInfo methodInfo = delegateType.GetMethod("Invoke");

      ParameterInfo[] parameterInfos = methodInfo.GetParameters();
      int parameterCount = parameterInfos.GetLength(0);

      Type[] parameterTypes = new Type[parameterCount];
      for (int i = 0; i < parameterCount; i++)
        parameterTypes[i] = parameterInfos[i].ParameterType;

      MethodBuilder methodBuilder = typeBuilder.DefinePInvokeMethod(
        dllImportAttribute.EntryPoint, dllImportAttribute.Value,
        MethodAttributes.Public | MethodAttributes.Static |
        MethodAttributes.PinvokeImpl, CallingConventions.Standard,
        methodInfo.ReturnType, parameterTypes,
        dllImportAttribute.CallingConvention,
        dllImportAttribute.CharSet);

      methodBuilder.SetCustomAttribute(new CustomAttributeBuilder(
        typeof(DefaultDllImportSearchPathsAttribute).GetConstructor(
          new Type[] { typeof(DllImportSearchPath) }),
        new object[] { dllImportSearchPath }));

      foreach (ParameterInfo parameterInfo in parameterInfos)
        methodBuilder.DefineParameter(parameterInfo.Position + 1,
          parameterInfo.Attributes, parameterInfo.Name);

      if (dllImportAttribute.PreserveSig)
        methodBuilder.SetImplementationFlags(MethodImplAttributes.PreserveSig);

      return typeBuilder.CreateType();
    }
  }
}