Visual C++多線程DAO處理 

 
　　在DAO多線程處理中，有許多局限性，所以我設(shè)計(jì)了這么一個類，通過GUI線程來使用DAO的強(qiáng)制調(diào)用。在類中使用了GUI的消息隊(duì)列，所有進(jìn)入到CMultiDAORecordset的調(diào)用都被迫使用AfxGetThread()來檢查當(dāng)前的線程。GUI線程指針是放在InitInstance的首端，如果在GUI線程中，引入的調(diào)用請求不在運(yùn)行，那么CMultiDAORecordSet就會發(fā)送一個WM_MULTIDAOMESSAGE消息給AfxGetMainWnd()（在Mainfrm.cpp中）。Mainfrm接受到這個消息，線程也就要再運(yùn)行一次，這個時候，消息已經(jīng)接受了，基類CDaoRecordset也就得到了調(diào)用。所以你的類是從CMultiDAORecordset繼承的，而不是CDaoRecordset，如下： 

class CMySet : public CMultiDaoRecordSet

在相應(yīng)的CPP文件中也應(yīng)該改一下：

IMPLEMENT_DYNAMIC(CMySet, CMultiDaoRecordSet)

CMySet::CMySet (CDaoDatabase* pdb) : CMultiDaoRecordSet(pdb) 
為了處理接受到的WM_MULTIDAOMESSAGE消息，下面的代碼還應(yīng)該加在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; 
} 

下面的代碼是加在對應(yīng)的應(yīng)用程序?qū)ο蟮念^文件中的：
public:
CWinThread *pGUIThread;

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


CMyApp::CMyApp()
{
pGUIThread = AfxGetThread();
}
 

　　如果沒有上面的定義的話，你的應(yīng)用程序就會出問題。整個DAO公共函數(shù)并沒有全部實(shí)現(xiàn)，但不管怎么樣，上面的函數(shù)是保護(hù)CDaoRecordset的使用的。如果你要加個函數(shù)的話，加進(jìn)去就行了，你也可以用一個對話框來顯示錯誤信息，它們都應(yīng)該在MultiDaorecordset.h中被定義。為了支持DAO多線程的類，下面的代碼也應(yīng)該加進(jìn)去：

加在Multidaorecordset.cpp中：
// MultiDaoRecordSet.cpp : implementation file 
// 

#define MULTIDAORECORDSET_CPP 

#include "stdafx.h" 

#include "MyApp.h" 

#include "MultiDaoRecordSet.h" 

#include "mainfrm.h" 

#ifdef _DEBUG 
#define new DEBUG_NEW 
#undef THIS_FILE 
static char THIS_FILE[] = __FILE__; 
#endif 

///////////////////////////////////////////////////////////////////////////// 
// CMultiDaoRecordSet 

IMPLEMENT_DYNAMIC(CMultiDaoRecordSet, CDaoRecordset) 

CMultiDaoRecordSet::CMultiDaoRecordSet(CDaoDatabase* pdb) 
: CDaoRecordset(pdb) 
{ 
//{{AFX_FIELD_INIT(CMultiDaoRecordSet) 
//}}AFX_FIELD_INIT 
m_nDefaultType = dbOpenDynaset; 
} 

//jtm 
//thread safe destructor.... 
CMultiDaoRecordSet::~CMultiDaoRecordSet() 
{ 
if (IsOpen()) 
Close(); 

// Clean up database if necessary 
if (m_pDatabase != NULL && (m_nStatus & AFX_DAO_IMPLICIT_DB)) 
{ 
m_pDatabase->Close(); 
delete m_pDatabase; 
m_pDatabase = NULL; 
} 
} 

CString CMultiDaoRecordSet::GetDefaultDBName() 
{ 
CMyApp *pApp = ((CMYApp *)AfxGetApp()); 
return pApp->GetDatabaseFullPath(); 
} 

///////////////////////////////////////////////////////////////////////////// 
// CMultiDaoRecordSet diagnostics 

//jtm 
//multi thread safe functoins 
void CMultiDaoRecordSet::Open(int nOpenType, LPCTSTR lpszSQL, int nOptions) 
{ 
CMYApp *pApp = ((CMYApp *)AfxGetApp()); 
if (pApp->pGUIThread == AfxGetThread()) 
{ 
CDaoRecordset::Open(nOpenType, lpszSQL, nOptions); 
} 
else 
{ 
pParam1 = (void *)&nOpenType; 
pParam2 = (void *)lpszSQL; 
pParam3 = (void *)&nOptions; 
AfxGetMainWnd()->SendMessage(WM_MULTIDAOMESSAGE, MultiDaoOpen, (LPARAM)this); 
} 
} 

void CMultiDaoRecordSet::Close() 
{ 
CMYApp *pApp = ((CMYApp *)AfxGetApp()); 
if (pApp->pGUIThread == AfxGetThread()) 
{ 
CDaoRecordset::Close(); 
} 
else 
{ 
AfxGetMainWnd()->SendMessage(WM_MULTIDAOMESSAGE, MultiDaoClose, (LPARAM)this); 
} 
} 

BOOL CMultiDaoRecordSet::IsOpen() 
{ 
CMYApp *pApp = ((CMYApp *)AfxGetApp()); 
if (pApp->pGUIThread == AfxGetThread()) 
{ 
return CDaoRecordset::IsOpen(); 
} 
else 
{ 
return (BOOL)AfxGetMainWnd()-> 
SendMessage(WM_MULTIDAOMESSAGE, MultiDaoIsOpen, (LPARAM)this); 
} 
} 

BOOL CMultiDaoRecordSet::IsBOF() 
{ 
CMYApp *pApp = ((CMYApp *)AfxGetApp()); 
if (pApp->pGUIThread == AfxGetThread()) 
{ 
return CDaoRecordset::IsBOF(); 
} 
else 
{ 
return (BOOL)AfxGetMainWnd()-> 
SendMessage(WM_MULTIDAOMESSAGE, MultiDaoIsBOF, (LPARAM)this); 
} 
} 

BOOL CMultiDaoRecordSet::IsEOF() 
{ 
CMYApp *pApp = ((CMYApp *)AfxGetApp()); 
if (pApp->pGUIThread == AfxGetThread()) 
{ 
return CDaoRecordset::IsEOF(); 
} 
else 
{ 
return (BOOL)AfxGetMainWnd()-> 
SendMessage(WM_MULTIDAOMESSAGE, MultiDaoIsEOF, (LPARAM)this); 
} 
} 

BOOL CMultiDaoRecordSet::IsDeleted() 
{ 
CMYApp *pApp = ((CMYApp *)AfxGetApp()); 
if (pApp->pGUIThread == AfxGetThread()) 
{ 
return CDaoRecordset::IsDeleted(); 
} 
else 
{ 
return (BOOL)AfxGetMainWnd()-> 
SendMessage(WM_MULTIDAOMESSAGE, MultiDaoIsDeleted, (LPARAM)this); 
} 
} 

BOOL CMultiDaoRecordSet::IsFieldDirty(void* pv) 
{ 
CMYApp *pApp = ((CMYApp *)AfxGetApp()); 
if (pApp->pGUIThread == AfxGetThread()) 
{ 
return CDaoRecordset::IsFieldDirty(pv); 
} 
else 
{ 
pParam1 = pv; 
return (BOOL)AfxGetMainWnd()-> 
SendMessage(WM_MULTIDAOMESSAGE, MultiDaoIsFieldDirty, (LPARAM)this); 
} 
} 

BOOL CMultiDaoRecordSet::IsFieldNull(void* pv) 
{ 
CMYApp *pApp = ((CMYApp *)AfxGetApp()); 
if (pApp->pGUIThread == AfxGetThread()) 
{ 
return CDaoRecordset::IsFieldNull(pv); 
} 
else 
{ 
pParam1 = pv; 
return (BOOL)AfxGetMainWnd()-> 
SendMessage(WM_MULTIDAOMESSAGE, MultiDaoIsFieldNull, (LPARAM)this); 
} 
} 

BOOL CMultiDaoRecordSet::IsFieldNullable(void* pv) 
{ 
CMYApp *pApp = ((CMYApp *)AfxGetApp()); 
if (pApp->pGUIThread == AfxGetThread()) 
{ 
return CDaoRecordset::IsFieldNullable(pv); 
} 
else 
{ 
pParam1 = pv; 
return (BOOL)AfxGetMainWnd()-> 
SendMessage(WM_MULTIDAOMESSAGE, MultiDaoIsFieldNullable, (LPARAM)this); 
} 
} 

CString CMultiDaoRecordSet::GetName() 
{ 
CMYApp *pApp = ((CMYApp *)AfxGetApp()); 
if (pApp->pGUIThread == AfxGetThread()) 
{ 
return CDaoRecordset::GetName(); 
} 
else 
{ 
return (CString)*(CString *)AfxGetMainWnd()-> 
SendMessage(WM_MULTIDAOMESSAGE, MultiDaoGetName, (LPARAM)this); 
} 
} 

short CMultiDaoRecordSet::GetType() 
{ 
CMYApp *pApp = ((CMYApp *)AfxGetApp()); 
if (pApp->pGUIThread == AfxGetThread()) 
{ 
return CDaoRecordset::GetType(); 
} 
else 
{ 
return (short)AfxGetMainWnd()-> 
SendMessage(WM_MULTIDAOMESSAGE, MultiDaoGetType, (LPARAM)this); 
} 
} 

short CMultiDaoRecordSet::GetEditMode() 
{ 
CMYApp *pApp = ((CMYApp *)AfxGetApp()); 
if (pApp->pGUIThread == AfxGetThread()) 
{ 
return CDaoRecordset::GetEditMode(); 
} 
else 
{ 
return (short)AfxGetMainWnd()-> 
SendMessage(WM_MULTIDAOMESSAGE, MultiDaoGetEditMode, (LPARAM)this); 
} 
} 

CString CMultiDaoRecordSet::GetSQL() 
{ 
CMYApp *pApp = ((CMYApp *)AfxGetApp()); 
if (pApp->pGUIThread == AfxGetThread()) 
{ 
return CDaoRecordset::GetSQL(); 
} 
else 
{ 
return (CString)*(CString *)AfxGetMainWnd()-> 
SendMessage(WM_MULTIDAOMESSAGE, MultiDaoGetSQL, (LPARAM)this); 
} 
} 

COleVariant CMultiDaoRecordSet::GetLastModifiedBookmark() 
{ 
CMYApp *pApp = ((CMYApp *)AfxGetApp()); 
if (pApp->pGUIThread == AfxGetThread()) 
{ 
return CDaoRecordset::GetLastModifiedBookmark(); 
} 
else 
{ 
return (COleVariant)AfxGetMainWnd()-> 
SendMessage(WM_MULTIDAOMESSAGE, MultiDaoGetLastModifiedBookmark, (LPARAM)this); 
} 
} 

long CMultiDaoRecordSet::GetRecordCount() 
{ 
CMYApp *pApp = ((CMYApp *)AfxGetApp()); 
if (pApp->pGUIThread == AfxGetThread())