我们知道ATL(活动模板库)是一套很小巧高效的COM开发库，它本身的核心文件其实没几个，COM相关的(主要是atlbase.h, atlcom.h)，另外还有一个窗口相关的(atlwin.h), 所以拿来学习应该是很方便的。但是因为ATL的代码充满了模板和宏，内部还夹杂着汇编，所以如果没有比较丰富的C++模板和系统底层的知识，一般人会看得一头雾水。
下面我们主要分析一下ATL中的一些汇编代码。
ATL中出现汇编代码主要是2处，一处是通过Thunk技术来调用类成员函数处理消息；还有一处是通过打开_ATL_DEBUG_INTERFACES宏来跟踪接口的引用计数。
通过Thunk技术来调用类成员函数
我们知道Windows窗口的消息处理函数要求是面向过程的C函数，所以我们C++普通成员函数就不能作为窗口的消息处理函数，所以这里的问题就是如何让我们的C++成员函数和Windows的窗口的消息处理函数关联起来？MFC是通过一个Map来实现的，而ATL选择了更为高效的Thunk技术来实现。
我们将主要代码贴出来，然后介绍它的创建过程:
template <class TBase, class TWinTraits>
HWND CWindowImplBaseT< TBase, TWinTraits >::Create(HWND hWndParent, RECT& rcPos, LPCTSTR szWindowName,
DWORD dwStyle, DWORD dwExStyle, UINT nID, ATOM atom, LPVOID lpCreateParam)
{
ATLASSERT(m_hWnd == NULL);
if(atom == 0)
return NULL;
_Module.AddCreateWndData(&m_thunk.cd, this);
if(nID == 0 && (dwStyle & WS_CHILD))
nID = (UINT)this;
HWND hWnd = ::CreateWindowEx(dwExStyle, (LPCTSTR)MAKELONG(atom, 0), szWindowName,
dwStyle, rcPos.left, rcPos.top, rcPos.right - rcPos.left,
rcPos.bottom - rcPos.top, hWndParent, (HMENU)nID,
_Module.GetModuleInstance(), lpCreateParam);
ATLASSERT(m_hWnd == hWnd);
return hWnd;
}
static LRESULT CALLBACK StartWindowProc(HWND hWnd, UINT uMsg,
WPARAM wParam, LPARAM lParam)
{
CContainedWindowT< TBase >* pThis = (CContainedWindowT< TBase >*)_Module.ExtractCreateWndData();
ATLASSERT(pThis != NULL);
pThis->m_hWnd = hWnd;
pThis->m_thunk.Init(WindowProc, pThis);
WNDPROC pProc = (WNDPROC)&(pThis->m_thunk.thunk);
WNDPROC pOldProc = (WNDPROC)::SetWindowLong(hWnd, GWL_WNDPROC, (LONG)pProc);
#ifdef _DEBUG
// check if somebody has subclassed us already since we discard it
if(pOldProc != StartWindowProc)
ATLTRACE2(atlTraceWindowing, 0, _T("Subclassing through a hook discarded.\n"));
#else
pOldProc; // avoid unused warning
#endif
return pProc(hWnd, uMsg, wParam, lParam);
}
class CWndProcThunk
{
public:
union
{
_AtlCreateWndData cd;
_WndProcThunk thunk;
};
void Init(WNDPROC proc, void* pThis)
{
#if defined (_M_IX86)
thunk.m_mov = 0x042444C7; //C7 44 24 0C
thunk.m_this = (DWORD)pThis;
thunk.m_jmp = 0xe9;
thunk.m_relproc = (int)proc - ((int)this+sizeof(_WndProcThunk));
#elif defined (_M_ALPHA)
thunk.ldah_at = (0x279f0000 | HIWORD(proc)) + (LOWORD(proc)>>15);
thunk.ldah_a0 = (0x261f0000 | HIWORD(pThis)) + (LOWORD(pThis)>>15);
thunk.lda_at = 0x239c0000 | LOWORD(proc);
thunk.lda_a0 = 0x22100000 | LOWORD(pThis);
thunk.jmp = 0x6bfc0000;
#endif
// write block from data cache and
// flush from instruction cache
FlushInstructionCache(GetCurrentProcess(), &thunk, sizeof(thunk));
}
};
static LRESULT CALLBACK WindowProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
CContainedWindowT< TBase >* pThis = (CContainedWindowT< TBase >*)hWnd;
ATLASSERT(pThis->m_hWnd != NULL);
ATLASSERT(pThis->m_pObject != NULL);
// set a ptr to this message and save the old value
MSG msg = { pThis->m_hWnd, uMsg, wParam, lParam, 0, { 0, 0 } };
const MSG* pOldMsg = pThis->m_pCurrentMsg;
pThis->m_pCurrentMsg = &msg;
// pass to the message map to process
LRESULT lRes;
BOOL bRet = pThis->m_pObject->ProcessWindowMessage(pThis->m_hWnd, uMsg, wParam, lParam, lRes, pThis->m_dwMsgMapID);
// restore saved value for the current message
ATLASSERT(pThis->m_pCurrentMsg == &msg);
pThis->m_pCurrentMsg = pOldMsg;
// do the default processing if message was not handled
if(!bRet)
{
if(uMsg != WM_NCDESTROY)
lRes = pThis->DefWindowProc(uMsg, wParam, lParam);
else
{
// unsubclass, if needed
LONG pfnWndProc = ::GetWindowLong(pThis->m_hWnd, GWL_WNDPROC);
lRes = pThis->DefWindowProc(uMsg, wParam, lParam);
if(pThis->m_pfnSuperWindowProc != ::DefWindowProc && ::GetWindowLong(pThis->m_hWnd, GWL_WNDPROC) == pfnWndProc)
::SetWindowLong(pThis->m_hWnd, GWL_WNDPROC, (LONG)pThis->m_pfnSuperWindowProc);
// clear out window handle
pThis->m_hWnd = NULL;
}
}
return lRes;
}
我们知道COM中引用计数的管理一直是个难题，因为你的接口是大家共用的，如果你引用计数管理出错，就会导致一些非常难查的问题，因此ATL中我们可以通过打开_ATL_DEBUG_INTERFACES宏 ，让我们通过Debug信息察看每个接口的引用计数情况。那么ATL是如何做到的呢？
相信用过ATL的人都会看到过这个代码：
static
HRESULT WINAPI InternalQueryInterface(void
* pThis, const
_ATL_INTMAP_ENTRY* pEntries, REFIID iid, void
** ppvObject) { ATLASSERT(pThis != NULL); // First entry in the com map should be a simple map entry
ATLASSERT(pEntries->pFunc == _ATL_SIMPLEMAPENTRY); #if
defined(_ATL_DEBUG_INTERFACES) || defined(_ATL_DEBUG_QI) LPCTSTR pszClassName = (LPCTSTR) pEntries[-1].dw; #endif
// _ATL_DEBUG_INTERFACES
HRESULT hRes = AtlInternalQueryInterface(pThis, pEntries, iid, ppvObject); #ifdef _ATL_DEBUG_INTERFACES _Module.AddThunk((IUnknown**)ppvObject, pszClassName, iid);
#endif
// _ATL_DEBUG_INTERFACES
return
_ATLDUMPIID(iid, pszClassName, hRes); }
HRESULT AddThunk(IUnknown** pp, LPCTSTR lpsz, REFIID iid)
{
if ((pp == NULL) || (*pp == NULL))
return E_POINTER;
IUnknown* p = *pp;
_QIThunk* pThunk = NULL;
EnterCriticalSection(&m_csObjMap);
// Check if exists already for identity
if (InlineIsEqualUnknown(iid))
{
for (int i = 0; i < m_paThunks->GetSize(); i++)
{
if (m_paThunks->operator[](i)->pUnk == p)
{
m_paThunks->operator[](i)->InternalAddRef();
pThunk = m_paThunks->operator[](i);
break;
}
}
}
if (pThunk == NULL)
{
++m_nIndexQI;
if (m_nIndexBreakAt == m_nIndexQI)
DebugBreak();
ATLTRY(pThunk = new _QIThunk(p, lpsz, iid, m_nIndexQI, (m_nIndexBreakAt == m_nIndexQI)));
if (pThunk == NULL)
return E_OUTOFMEMORY;
pThunk->InternalAddRef();
m_paThunks->Add(pThunk);
}
LeaveCriticalSection(&m_csObjMap);
*pp = (IUnknown*)pThunk;
return S_OK;
}
struct _QIThunk
{
STDMETHOD(QueryInterface)(REFIID iid, void** pp)
{
ATLASSERT(m_dwRef >= 0);
return pUnk->QueryInterface(iid, pp);
}
STDMETHOD_(ULONG, AddRef)()
{
if (bBreak)
DebugBreak();
pUnk->AddRef();
return InternalAddRef();
}
ULONG InternalAddRef()
{
if (bBreak)
DebugBreak();
ATLASSERT(m_dwRef >= 0);
long l = InterlockedIncrement(&m_dwRef);
ATLTRACE(_T("%d> "), m_dwRef);
AtlDumpIID(iid, lpszClassName, S_OK);
if (l > m_dwMaxRef)
m_dwMaxRef = l;
return l;
}
STDMETHOD_(ULONG, Release)();
STDMETHOD(f3)();
STDMETHOD(f4)();
....
STDMETHOD(f1023)();
STDMETHOD(f1024)();
_QIThunk(IUnknown* pOrig, LPCTSTR p, const IID& i, UINT n, bool b)
{
lpszClassName = p;
iid = i;
nIndex = n;
m_dwRef = 0;
m_dwMaxRef = 0;
pUnk = pOrig;
bBreak = b;
bNonAddRefThunk = false;
}
IUnknown* pUnk;
long m_dwRef;
long m_dwMaxRef;
LPCTSTR lpszClassName;
IID iid;
UINT nIndex;
bool bBreak;
bool bNonAddRefThunk;
};
#define IMPL_THUNK(n)\
__declspec(naked) inline HRESULT _QIThunk::f##n()\
{\
__asm mov eax, [esp+4]\
__asm cmp dword ptr [eax+8], 0\
__asm jg goodref\
__asm call atlBadThunkCall\
__asm goodref:\
__asm mov eax, [esp+4]\
__asm mov eax, dword ptr [eax+4]\
__asm mov [esp+4], eax\
__asm mov eax, dword ptr [eax]\
__asm mov eax, dword ptr [eax+4*n]\
__asm jmp eax\
}
IMPL_THUNK(3)
IMPL_THUNK(4)
IMPL_THUNK(5)
....
