什么是thunk技术实现？

/************************ Copyright (c) 2013 ************************

功能描述:

    thunk技术实现.利用这个类可以把回调函数完全封装成类成员函数.

调用示例:

 //导入头文件及库文件

 #include "ZThunk.h"

 class CTimer

 {

 private:

  // 此对像必须声时为类的数据成员或者全局对像,以保证它的生命周期

  ZThunk m_thunk;

 public:

  

  //安装定时器

  void Set()

  {

   //计算回调函数地址

   void* pAddr=m_thunk.Callback(this,&CTimer::TimerProc,ZThunk::THISCALL);

   // 此为安装定器函数的原形

   // UINT_PTR SetTimer(

   // HWND hWnd,              // 窗口句柄

   // UINT_PTR nIDEvent,      // 定时器ID

   // UINT uElapse,           // 时间间隔

   // TIMERPROC lpTimerFunc   // 定时器回调函数

   

   //安装计时器

   SetTimer(NULL,1,1000,(TIMERPROC)pAddr); 

  }

  //定时器回调函数,完全被封装成类成员函数!

  void TimerProc(HWND hWnd, DWORD dwMsg , WPARAM wPa, LPARAM lPa)

  {

   // to do something

  }

 };

************************ Copyright (c) 2006 ************************/

/*

网络上流行的Thunk技术，主要用于将成员函数变为线程函数或窗口过程.

弥补了static成员函数不能访问非静态成员数据的缺点，

最典型的应用就是微软的MFC和ATL中的窗口类实现，此原码也是网上公开的一个Thunk类

*/

#ifndef _ZTHUNK

#define _ZTHUNK

class ZThunk 

{

private:

 unsigned char m_ThiscallCode[10];

 unsigned char m_StdcallCode[16];

public:

 enum CALLINGCONVENTIONS

 {

  STDCALL = 1,

  THISCALL= 2

 };

public:

 template <class T>

 void* Callback(void* pThis,T MemberOffset,CALLINGCONVENTIONS CallingConvention = STDCALL)

 {

  // these codes only use in stdcall

  if(CallingConvention == STDCALL)

  {

   // Encoded machine instruction   Equivalent assembly languate notation

   // ---------------------------   -------------------------------------

   // FF 34 24                      push  dword ptr [esp]          ; Save (or duplicate)                                                                    ; the Return Addr into stack

   // C7 44 24 04 ?? ?? ?? ??       mov   dword ptr [esp+4], pThis ; Overwite the old                                                                    ; Return Addr with 'this pointer'

   // E9 ?? ?? ?? ??                jmp   target addr              ; Jump to target message handler

   char Buf[33]={0};

   sprintf(Buf,"%d",MemberOffset);

   unsigned long JmpAddr = (unsigned long) atol(Buf) - (unsigned long) &m_StdcallCode[0] - 16;

   m_StdcallCode[11] = 0xE9;

   *((unsigned long *)  &m_StdcallCode[ 0]) = 0x002434FF;

   *((unsigned long *)  &m_StdcallCode[ 3]) = 0x042444C7;

   *((unsigned long *)  &m_StdcallCode[ 7]) = (unsigned long) pThis;

   *((unsigned long *)  &m_StdcallCode[12]) = JmpAddr;

   return (void*)m_StdcallCode;

  }

  // these codes only use in thiscall

  else if(CallingConvention == THISCALL)

  {

   // Encoded machine instruction   Equivalent assembly languate notation

   // ---------------------------   -------------------------------------

   // B9 ?? ?? ?? ??                mov    ecx, pThis  ; Load ecx with this pointer

   // E9 ?? ?? ?? ??                jmp    target addr ; Jump to target message handler

   char Buf[33]={0};

   sprintf(Buf,"%d",MemberOffset);

   unsigned long JmpAddr = (unsigned long) atol(Buf) - (unsigned long) &m_ThiscallCode[0] - 10;

   m_ThiscallCode[0] = 0xB9;

   m_ThiscallCode[5] = 0xE9;

   *((unsigned long *) &m_ThiscallCode[1]) = (unsigned long) pThis;

   *((unsigned long *) &m_ThiscallCode[6]) = JmpAddr;

   return (void*)m_ThiscallCode;

  }return 0;

 }

};

#endif