Visual C++多线程DAO处理

在DAO多线程处理中，有许多局限性，所以我设计了这么一个类，通过GUI线程来使用DAO的强制调用。在类中使用了GUI的消息队列，所有进入到CMultiDAORecordset的调用都被迫使用AfxGetThread()来检查当前的线程。GUI线程指针是放在InitInstance的首端，如果在GUI线程中，引入的调用请求不在运行，那么CMultiDAORecordSet就会 发送一个WM_MULTIDAOMESSAGE消息给AfxGetMainWnd()（在Mainfrm.cpp中）。Mainfrm接受到这个消息，线程也就要再运行一次，这个时候，消息已经接受了，基类CDaoRecordset也就得到了调用。所以你的类是从CMultiDAORecordset继承的，而不是CDaoRecordset，如下：

class CMySet : public CMultiDaoRecordSet

在相应的CPP文件中也应该改一下：

IMPLEMENT_DYNAMIC(CMySet, CMultiDaoRecordSet)

CMySet::CMySet (CDaoDatabase* pdb) : CMultiDaoRecordSet(pdb)

为了处理接受到的WM_MULTIDAOMESSAGE消息，下面的代码还应该加在MainFrm中：

在MainFrm.h文件中加：

#ifdef MAINFRAME_CPP

UINT WM_MULTIDAOMESSAGE = RegisterWindowMessage("WM_MULTIDAOMESSAGE");

#else

extern UINT WM_MULTIDAOMESSAGE;

#endif

afx_msg LONG OnMultiDaoMessage( UINT uParam, LONG lParam);

在MainFrm.cpp文件中加：

#define MAINFRAME_CPP

#include "MutliDaoRecordset.h"

//added to the message map

BEGIN_MESSAGE_MAP(CMainFrame, CMDIFrameWnd)

//{{AFX_MSG_MAP(CMainFrame)

ON_REGISTERED_MESSAGE(WM_MULTIDAOMESSAGE, OnMultiDaoMessage)

END_MESSAGE_MAP()

//this function added

LONG CMainFrame::OnMultiDaoMessage( UINT uParam, LONG lParam)

{

//jtm

//based on switch, perform operation...

CMultiDaoRecordSet *pSet = (CMultiDaoRecordSet *)lParam;

LONG lRet = 0;

CString cRet = "";

COleVariant cVar;

try

{

//jtm-------debug--------------------------------------

CString cTraceMessage = cDAOMessageArray[uParam];

cTraceMessage += "\n";

TRACE(cTraceMessage);

//jtm-------debug--------------------------------------

switch(uParam)

{

case MultiDaoOpen:

pSet->Open();

break;

case MultiDaoClose:

pSet->Close();

break;

case MultiDaoIsOpen:

lRet = (LONG)pSet->IsOpen();

break;

case MultiDaoIsBOF:

lRet = (LONG)pSet->IsBOF();

break;

case MultiDaoIsEOF:

lRet = (LONG)pSet->IsEOF();

break;

case MultiDaoIsDeleted:

lRet = (LONG)pSet->IsDeleted();

break;

case MultiDaoIsFieldDirty:

lRet = (LONG)pSet->IsFieldDirty(pSet->pParam1);

break;

case MultiDaoIsFieldNull:

lRet = (LONG)pSet->IsFieldNull(pSet->pParam1);

break;

case MultiDaoIsFieldNullable:

lRet = (LONG)pSet->IsFieldNullable(pSet->pParam1);

break;

case MultiDaoGetName:

cRet = pSet->GetName();

lRet = (LONG)&cRet;

break;

case MultiDaoGetType:

lRet = (LONG)pSet->GetType();

break;

case MultiDaoGetEditMode:

lRet = (LONG)pSet->GetEditMode();

break;

case MultiDaoGetLastModifiedBookmark:

cVar = pSet->GetLastModifiedBookmark();

lRet = (LONG)&cVar;

break;

case MultiDaoGetRecordCount:

lRet = (LONG)pSet->GetRecordCount();

break;

case MultiDaoMoveNext:

pSet->MoveNext();

break;

case MultiDaoMovePrev:

pSet->MovePrev();

break;

case MultiDaoMoveFirst:

pSet->MoveFirst();

break;

case MultiDaoMoveLast:

pSet->MoveLast();

break;

case MultiDaoMove:

pSet->Move(*(LONG *)pSet->pParam1);

break;

case MultiDaoFindNext:

lRet = (LONG)pSet->FindNext(*(LPCTSTR *)pSet->pParam1);

break;

case MultiDaoFindPrev:

lRet = (LONG)pSet->FindPrev(*(LPCTSTR*)pSet->pParam1);

break;

case MultiDaoFindFirst:

lRet = (LONG)pSet->FindFirst(*(LPCTSTR *)pSet->pParam1);

break;

case MultiDaoFindLast:

lRet = (LONG)pSet->FindLast(*(LPCTSTR *)pSet->pParam1);

break;

case MultiDaoFind:

lRet = (LONG)pSet->Find(*(LONG *)pSet->pParam1, *(LPCTSTR*)pSet->pParam2);

break;

case MultiDaoGetBookmark:

cVar = pSet->GetBookmark();

lRet = (LONG)&cVar;

break;

case MultiDaoSetBookmark:

pSet->SetBookmark(*(COleVariant*)pSet->pParam1);

break;

case MultiDaoAddNew:

pSet->AddNew();

break;

case MultiDaoEdit:

pSet->Edit();

break;

case MultiDaoUpdate:

pSet->Update();

break;

case MultiDaoDelete:

pSet->Delete();

break;

case MultiDaoCancelUpdate:

pSet->CancelUpdate();

break;

case MultiDaoRequery:

pSet->Requery();

break;

}

}

catch (CDaoException *e)

{

TRACE("Database Multithread Operation Failed%s\n",

e->m_pErrorInfo->m_strDescription);

}

return lRet;

}

下面的代码是加在对应的应用程序对象的头文件中的：

public:

CWinThread *pGUIThread;

And this to the constructor in the app .cpp file:

CMyApp::CMyApp()

{

pGUIThread = AfxGetThread();

}