1、創(chuàng)建和終止線程
在MFC程序中創(chuàng)建一個線程，宜調(diào)用AfxBeginThread函數(shù)。該函數(shù)因參數(shù)不同而具有兩種重載版本，分別對應工作者線程和用戶接口（UI）線程。
工作者線程
| CWinThread *AfxBeginThread( AFX_THREADPROC pfnThreadProc, //控制函數(shù) LPVOID pParam, //傳遞給控制函數(shù)的參數(shù) int nPriority = THREAD_PRIORITY_NORMAL, //線程的優(yōu)先級 UINT nStackSize = 0, //線程的堆棧大小 DWORD dwCreateFlags = 0, //線程的創(chuàng)建標志 LPSECURITY_ATTRIBUTES lpSecurityAttrs = NULL //線程的安全屬性 ); |
| //線程控制函數(shù) UINT MfcThreadProc(LPVOID lpParam) { CExampleClass *lpObject = (CExampleClass*)lpParam; if (lpObject == NULL || !lpObject->IsKindof(RUNTIME_CLASS(CExampleClass))) return - 1; //輸入?yún)?shù)非法 //線程成功啟動 while (1) { ...// } return 0; } //在MFC程序中啟動線程 AfxBeginThread(MfcThreadProc, lpObject); |
| class CWinThread : public CCmdTarget { DECLARE_DYNAMIC(CWinThread) public: // Constructors CWinThread(); BOOL CreateThread(DWORD dwCreateFlags = 0, UINT nStackSize = 0, LPSECURITY_ATTRIBUTES lpSecurityAttrs = NULL); // Attributes CWnd* m_pMainWnd; // main window (usually same AfxGetApp()->m_pMainWnd) CWnd* m_pActiveWnd; // active main window (may not be m_pMainWnd) BOOL m_bAutoDelete; // enables 'delete this' after thread termination // only valid while running HANDLE m_hThread; // this thread's HANDLE operator HANDLE() const; DWORD m_nThreadID; // this thread's ID int GetThreadPriority(); BOOL SetThreadPriority(int nPriority); // Operations DWORD SuspendThread(); DWORD ResumeThread(); BOOL PostThreadMessage(UINT message, WPARAM wParam, LPARAM lParam); // Overridables //執(zhí)行線程實例初始化，必須重寫 virtual BOOL InitInstance(); // running and idle processing //控制線程的函數(shù)，包含消息泵，一般不重寫 virtual int Run(); //消息調(diào)度到TranslateMessage和DispatchMessage之前對其進行篩選， //通常不重寫 virtual BOOL PreTranslateMessage(MSG* pMsg); virtual BOOL PumpMessage(); // low level message pump //執(zhí)行線程特定的閑置時間處理，通常不重寫 virtual BOOL OnIdle(LONG lCount); // return TRUE if more idle processing virtual BOOL IsIdleMessage(MSG* pMsg); // checks for special messages //線程終止時執(zhí)行清除，通常需要重寫 virtual int ExitInstance(); // default will 'delete this' //截獲由線程的消息和命令處理程序引發(fā)的未處理異常，通常不重寫 virtual LRESULT ProcessWndProcException(CException* e, const MSG* pMsg); // Advanced: handling messages sent to message filter hook virtual BOOL ProcessMessageFilter(int code, LPMSG lpMsg); // Advanced: virtual access to m_pMainWnd virtual CWnd* GetMainWnd(); // Implementation public: virtual ~CWinThread(); #ifdef _DEBUG virtual void AssertValid() const; virtual void Dump(CDumpContext& dc) const; int m_nDisablePumpCount; // Diagnostic trap to detect illegal re-entrancy #endif void CommonConstruct(); virtual void Delete(); // 'delete this' only if m_bAutoDelete == TRUE // message pump for Run MSG m_msgCur; // current message public: // constructor used by implementation of AfxBeginThread CWinThread(AFX_THREADPROC pfnThreadProc, LPVOID pParam); // valid after construction LPVOID m_pThreadParams; // generic parameters passed to starting function AFX_THREADPROC m_pfnThreadProc; // set after OLE is initialized void (AFXAPI* m_lpfnOleTermOrFreeLib)(BOOL, BOOL); COleMessageFilter* m_pMessageFilter; protected: CPoint m_ptCursorLast; // last mouse position UINT m_nMsgLast; // last mouse message BOOL DispatchThreadMessageEx(MSG* msg); // helper void DispatchThreadMessage(MSG* msg); // obsolete }; |
| CWinThread *AfxBeginThread( //從CWinThread派生的類的 RUNTIME_CLASS CRuntimeClass *pThreadClass, int nPriority = THREAD_PRIORITY_NORMAL, UINT nStackSize = 0, DWORD dwCreateFlags = 0, LPSECURITY_ATTRIBUTES lpSecurityAttrs = NULL ); |
 |
| ///////////////////////////////////////////////////////////////////////////// // CMyUIThread thread class CMyUIThread : public CWinThread { DECLARE_DYNCREATE(CMyUIThread) protected: CMyUIThread(); // protected constructor used by dynamic creation // Attributes public: // Operations public: // Overrides // ClassWizard generated virtual function overrides //{{AFX_VIRTUAL(CMyUIThread) public: virtual BOOL InitInstance(); virtual int ExitInstance(); //}}AFX_VIRTUAL // Implementation protected: virtual ~CMyUIThread(); // Generated message map functions //{{AFX_MSG(CMyUIThread) // NOTE - the ClassWizard will add and remove member functions here. //}}AFX_MSG DECLARE_MESSAGE_MAP() }; ///////////////////////////////////////////////////////////////////////////// // CMyUIThread IMPLEMENT_DYNCREATE(CMyUIThread, CWinThread) CMyUIThread::CMyUIThread() {} CMyUIThread::~CMyUIThread() {} BOOL CMyUIThread::InitInstance() { // TODO: perform and per-thread initialization here return TRUE; } int CMyUIThread::ExitInstance() { // TODO: perform any per-thread cleanup here return CWinThread::ExitInstance(); } BEGIN_MESSAGE_MAP(CMyUIThread, CWinThread) //{{AFX_MSG_MAP(CMyUIThread) // NOTE - the ClassWizard will add and remove mapping macros here. //}}AFX_MSG_MAP END_MESSAGE_MAP() |
| CMyUIThread *pThread; pThread = (CMyUIThread*) AfxBeginThread( RUNTIME_CLASS(CMyUIThread) ); |
| void AfxEndThread( UINT nExitCode //the exit code of the thread ); |
2.線程間通信
MFC中定義了繼承自CSyncObject類的CCriticalSection、CCEvent、CMutex、CSemaphore類封裝和簡化了WIN32API所提供的臨界區(qū)、事件、互斥和信號量。使用這些同步機制，必須包含"Afxmt.h"頭文件。下圖給出了類的繼承關系：
 |
| class CSyncObject : public CObject { DECLARE_DYNAMIC(CSyncObject) // Constructor public: CSyncObject(LPCTSTR pstrName); // Attributes public: operator HANDLE() const; HANDLE m_hObject; // Operations virtual BOOL Lock(DWORD dwTimeout = INFINITE); virtual BOOL Unlock() = 0; virtual BOOL Unlock(LONG /* lCount */, LPLONG /* lpPrevCount=NULL */) { return TRUE; } // Implementation public: virtual ~CSyncObject(); #ifdef _DEBUG CString m_strName; virtual void AssertValid() const; virtual void Dump(CDumpContext& dc) const; #endif friend class CSingleLock; friend class CMultiLock; }; |
| class CThreadSafeWnd { public: CThreadSafeWnd(){} ~CThreadSafeWnd(){} void SetWindow(CWnd *pwnd) { m_pCWnd = pwnd; } void PaintBall(COLORREF color, CRect &rc); private: CWnd *m_pCWnd; CCriticalSection m_CSect; }; void CThreadSafeWnd::PaintBall(COLORREF color, CRect &rc) { CSingleLock csl(&m_CSect); //缺省的Timeout是INFINITE，只有m_Csect被激活，csl.Lock()才能返回 //true，這里一直等待 if (csl.Lock()) ; { // not necessary //AFX_MANAGE_STATE(AfxGetStaticModuleState( )); CDC *pdc = m_pCWnd->GetDC(); CBrush brush(color); CBrush *oldbrush = pdc->SelectObject(&brush); pdc->Ellipse(rc); pdc->SelectObject(oldbrush); GdiFlush(); // don't wait to update the display } } |
| int array1[10], array2[10]; CMutexSection section; //創(chuàng)建一個CMutex類的對象 //賦值線程控制函數(shù) UINT EvaluateThread(LPVOID param) { CSingleLock singlelock; singlelock(§ion); //互斥區(qū)域 singlelock.Lock(); for (int i = 0; i < 10; i++) array1[i] = i; singlelock.Unlock(); } //拷貝線程控制函數(shù) UINT CopyThread(LPVOID param) { CSingleLock singlelock; singlelock(§ion); //互斥區(qū)域 singlelock.Lock(); for (int i = 0; i < 10; i++) array2[i] = array1[i]; singlelock.Unlock(); } } AfxBeginThread(EvaluateThread, NULL); //啟動賦值線程 AfxBeginThread(CopyThread, NULL); //啟動拷貝線程 |
| for (int i = 0; i < 10; i++) array1[i] = i; |
| for (int i = 0; i < 10; i++) array2[i] = array1[i]; |
| BOOL PostThreadMessage(DWORD idThread, // thread identifier UINT Msg, // message to post WPARAM wParam, // first message parameter LPARAM lParam // second message parameter ); |
3.線程與消息隊列
在WIN32中，每一個線程都對應著一個消息隊列。由于一個線程可以產(chǎn)生數(shù)個窗口，所以并不是每個窗口都對應著一個消息隊列。下列幾句話應該作為"定理"被記?。?br>
"定理" 一
所有產(chǎn)生給某個窗口的消息，都先由創(chuàng)建這個窗口的線程處理；
"定理" 二
Windows屏幕上的每一個控件都是一個窗口，有對應的窗口函數(shù)。
消息的發(fā)送通常有兩種方式，一是SendMessage，一是PostMessage，其原型分別為：
| LRESULT SendMessage(HWND hWnd, // handle of destination window UINT Msg, // message to send WPARAM wParam, // first message parameter LPARAM lParam // second message parameter ); BOOL PostMessage(HWND hWnd, // handle of destination window UINT Msg, // message to post WPARAM wParam, // first message parameter LPARAM lParam // second message parameter ); |
兩個函數(shù)原型中的四個參數(shù)的意義相同，但是SendMessage和PostMessage的行為有差異。SendMessage必須等待消息被處理后才返回，而PostMessage僅僅將消息放入消息隊列。SendMessage的目標窗口如果屬于另一個線程，則會發(fā)生線程上下文切換，等待另一線程處理完成消息。為了防止另一線程當?shù)?，導致SendMessage永遠不能返回，我們可以調(diào)用SendMessageTimeout函數(shù)：
| LRESULT SendMessageTimeout( HWND hWnd, // handle of destination window UINT Msg, // message to send WPARAM wParam, // first message parameter LPARAM lParam, // second message parameter UINT fuFlags, // how to send the message UINT uTimeout, // time-out duration LPDWORD lpdwResult // return value for synchronous call ); |
4. MFC線程、消息隊列與MFC程序的"生死因果"
分析MFC程序的主線程啟動及消息隊列處理的過程將有助于我們進一步理解UI線程與消息隊列的關系，為此我們需要簡單地敘述一下MFC程序的"生死因果"（侯捷：《深入淺出MFC》）。
使用VC++ 6.0的向導完成一個最簡單的單文檔架構MFC應用程序MFCThread：
（1） 輸入MFC EXE工程名MFCThread；
（2） 選擇單文檔架構，不支持Document/View結構；
（3） ActiveX、3D container等其他選項都選擇無。
我們來分析這個工程。下面是產(chǎn)生的核心源代碼：
MFCThread.h 文件
| class CMFCThreadApp : public CWinApp { public: CMFCThreadApp(); // Overrides // ClassWizard generated virtual function overrides //{{AFX_VIRTUAL(CMFCThreadApp) public: virtual BOOL InitInstance(); //}}AFX_VIRTUAL // Implementation public: //{{AFX_MSG(CMFCThreadApp) afx_msg void OnAppAbout(); // NOTE - the ClassWizard will add and remove member functions here. // DO NOT EDIT what you see in these blocks of generated code ! //}}AFX_MSG DECLARE_MESSAGE_MAP() }; |
MFCThread.cpp文件
| CMFCThreadApp theApp; ///////////////////////////////////////////////////////////////////////////// // CMFCThreadApp initialization BOOL CMFCThreadApp::InitInstance() { … CMainFrame* pFrame = new CMainFrame; m_pMainWnd = pFrame; // create and load the frame with its resources pFrame->LoadFrame(IDR_MAINFRAME,WS_OVERLAPPEDWINDOW | FWS_ADDTOTITLE, NULL,NULL); // The one and only window has been initialized, so show and update it. pFrame->ShowWindow(SW_SHOW); pFrame->UpdateWindow(); return TRUE; } |
MainFrm.h文件
| #include "ChildView.h" class CMainFrame : public CFrameWnd { public: CMainFrame(); protected: DECLARE_DYNAMIC(CMainFrame) // Attributes public: // Operations public: // Overrides // ClassWizard generated virtual function overrides //{{AFX_VIRTUAL(CMainFrame) virtual BOOL PreCreateWindow(CREATESTRUCT& cs); virtual BOOL OnCmdMsg(UINT nID, int nCode, void* pExtra, AFX_CMDHANDLERINFO* pHandlerInfo); //}}AFX_VIRTUAL // Implementation public: virtual ~CMainFrame(); #ifdef _DEBUG virtual void AssertValid() const; virtual void Dump(CDumpContext& dc) const; #endif CChildView m_wndView; // Generated message map functions protected: //{{AFX_MSG(CMainFrame) afx_msg void OnSetFocus(CWnd *pOldWnd); // NOTE - the ClassWizard will add and remove member functions here. // DO NOT EDIT what you see in these blocks of generated code! //}}AFX_MSG DECLARE_MESSAGE_MAP() }; |
MainFrm.cpp文件
| IMPLEMENT_DYNAMIC(CMainFrame, CFrameWnd) BEGIN_MESSAGE_MAP(CMainFrame, CFrameWnd) //{{AFX_MSG_MAP(CMainFrame) // NOTE - the ClassWizard will add and remove mapping macros here. // DO NOT EDIT what you see in these blocks of generated code ! ON_WM_SETFOCUS() //}}AFX_MSG_MAP END_MESSAGE_MAP() ///////////////////////////////////////////////////////////////////////////// // CMainFrame construction/destruction CMainFrame::CMainFrame() { // TODO: add member initialization code here } CMainFrame::~CMainFrame() {} BOOL CMainFrame::PreCreateWindow(CREATESTRUCT& cs) { if( !CFrameWnd::PreCreateWindow(cs) ) return FALSE; // TODO: Modify the Window class or styles here by modifying // the CREATESTRUCT cs cs.dwExStyle &= ~WS_EX_CLIENTEDGE; cs.lpszClass = AfxRegisterWndClass(0); return TRUE; } |
ChildView.h文件
| // CChildView window class CChildView : public CWnd { // Construction public: CChildView(); // Attributes public: // Operations public: // Overrides // ClassWizard generated virtual function overrides //{{AFX_VIRTUAL(CChildView) protected: virtual BOOL PreCreateWindow(CREATESTRUCT& cs); //}}AFX_VIRTUAL // Implementation public: virtual ~CChildView(); // Generated message map functions protected: //{{AFX_MSG(CChildView) afx_msg void OnPaint(); //}}AFX_MSG DECLARE_MESSAGE_MAP() }; ChildView.cpp文件 // CChildView CChildView::CChildView() {} CChildView::~CChildView() {} BEGIN_MESSAGE_MAP(CChildView,CWnd ) //{{AFX_MSG_MAP(CChildView) ON_WM_PAINT() //}}AFX_MSG_MAP END_MESSAGE_MAP() ///////////////////////////////////////////////////////////////////////////// // CChildView message handlers BOOL CChildView::PreCreateWindow(CREATESTRUCT& cs) { if (!CWnd::PreCreateWindow(cs)) return FALSE; cs.dwExStyle |= WS_EX_CLIENTEDGE; cs.style &= ~WS_BORDER; cs.lpszClass = AfxRegisterWndClass(CS_HREDRAW|CS_VREDRAW|CS_DBLCLKS,::LoadCursor(NULL, IDC_ARROW), HBRUSH(COLOR_WINDOW+1),NULL); return TRUE; } void CChildView::OnPaint() { CPaintDC dc(this); // device context for painting // TODO: Add your message handler code here // Do not call CWnd::OnPaint() for painting messages } |
文件MFCThread.h和MFCThread.cpp定義和實現(xiàn)的類CMFCThreadApp繼承自CWinApp類，而CWinApp類又繼承自CWinThread類（CWinThread類又繼承自CCmdTarget類），所以CMFCThread本質(zhì)上是一個MFC線程類，下圖給出了相關的類層次結構：
我們提取CWinApp類原型的一部分：
| class CWinApp : public CWinThread { DECLARE_DYNAMIC(CWinApp) public: // Constructor CWinApp(LPCTSTR lpszAppName = NULL);// default app name // Attributes // Startup args (do not change) HINSTANCE m_hInstance; HINSTANCE m_hPrevInstance; LPTSTR m_lpCmdLine; int m_nCmdShow; // Running args (can be changed in InitInstance) LPCTSTR m_pszAppName; // human readable name LPCTSTR m_pszExeName; // executable name (no spaces) LPCTSTR m_pszHelpFilePath; // default based on module path LPCTSTR m_pszProfileName; // default based on app name // Overridables virtual BOOL InitApplication(); virtual BOOL InitInstance(); virtual int ExitInstance(); // return app exit code virtual int Run(); virtual BOOL OnIdle(LONG lCount); // return TRUE if more idle processing virtual LRESULT ProcessWndProcException(CException* e,const MSG* pMsg); public: virtual ~CWinApp(); protected: DECLARE_MESSAGE_MAP() }; |
SDK程序的WinMain 所完成的工作現(xiàn)在由CWinApp 的三個函數(shù)完成：
| virtual BOOL InitApplication(); virtual BOOL InitInstance(); virtual int Run(); |
"CMFCThreadApp theApp;"語句定義的全局變量theApp是整個程式的applicationobject，每一個MFC 應用程序都有一個。當我們執(zhí)行MFCThread程序的時候，這個全局變量被構造。theApp配置完成后，WinMain開始執(zhí)行。但是程序中并沒有WinMain的代碼，它在哪里呢？原來MFC早已準備好并由Linker直接加到應用程序代碼中的，其原型為（存在于VC++6.0安裝目錄下提供的APPMODUL.CPP文件中）：
| extern "C" int WINAPI _tWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPTSTR lpCmdLine, int nCmdShow) { // call shared/exported WinMain return AfxWinMain(hInstance, hPrevInstance, lpCmdLine, nCmdShow); } |
其中調(diào)用的AfxWinMain如下（存在于VC++6.0安裝目錄下提供的WINMAIN.CPP文件中）：
| int AFXAPI AfxWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPTSTR lpCmdLine, int nCmdShow) { ASSERT(hPrevInstance == NULL); int nReturnCode = -1; CWinThread* pThread = AfxGetThread(); CWinApp* pApp = AfxGetApp(); // AFX internal initialization if (!AfxWinInit(hInstance, hPrevInstance, lpCmdLine, nCmdShow)) goto InitFailure; // App global initializations (rare) if (pApp != NULL && !pApp->InitApplication()) goto InitFailure; // Perform specific initializations if (!pThread->InitInstance()) { if (pThread->m_pMainWnd != NULL) { TRACE0("Warning: Destroying non-NULL m_pMainWnd\n"); pThread->m_pMainWnd->DestroyWindow(); } nReturnCode = pThread->ExitInstance(); goto InitFailure; } nReturnCode = pThread->Run(); InitFailure: #ifdef _DEBUG // Check for missing AfxLockTempMap calls if (AfxGetModuleThreadState()->m_nTempMapLock != 0) { TRACE1("Warning: Temp map lock count non-zero (%ld).\n", AfxGetModuleThreadState()->m_nTempMapLock); } AfxLockTempMaps(); AfxUnlockTempMaps(-1); #endif AfxWinTerm(); return nReturnCode; } |
我們提取主干，實際上，這個函數(shù)做的事情主要是：
| CWinThread* pThread = AfxGetThread(); CWinApp* pApp = AfxGetApp(); AfxWinInit(hInstance, hPrevInstance, lpCmdLine, nCmdShow) pApp->InitApplication() pThread->InitInstance() pThread->Run(); |
其中，InitApplication是注冊窗口類別的場所；InitInstance是產(chǎn)生窗口并顯示窗口的場所；Run是提取并分派消息的場所。這樣，MFC就同WIN32SDK程序對應起來了。CWinThread::Run是程序生命的"活水源頭"（侯捷：《深入淺出MFC》，函數(shù)存在于VC++6.0安裝目錄下提供的THRDCORE.CPP文件中）：
| // main running routine until thread exits int CWinThread::Run() { ASSERT_VALID(this); // for tracking the idle time state BOOL bIdle = TRUE; LONG lIdleCount = 0; // acquire and dispatch messages until a WM_QUIT message is received. for (;;) { // phase1: check to see if we can do idle work while (bIdle && !::PeekMessage(&m_msgCur, NULL, NULL, NULL, PM_NOREMOVE)) { // call OnIdle while in bIdle state if (!OnIdle(lIdleCount++)) bIdle = FALSE; // assume "no idle" state } // phase2: pump messages while available do { // pump message, but quit on WM_QUIT if (!PumpMessage()) return ExitInstance(); // reset "no idle" state after pumping "normal" message if (IsIdleMessage(&m_msgCur)) { bIdle = TRUE; lIdleCount = 0; } } while (::PeekMessage(&m_msgCur, NULL, NULL, NULL, PM_NOREMOVE)); } ASSERT(FALSE); // not reachable } |
其中的PumpMessage函數(shù)又對應于：
| ///////////////////////////////////////////////////////////////////////////// // CWinThread implementation helpers BOOL CWinThread::PumpMessage() { ASSERT_VALID(this); if (!::GetMessage(&m_msgCur, NULL, NULL, NULL)) { return FALSE; } // process this message if(m_msgCur.message != WM_KICKIDLE && !PreTranslateMessage(&m_msgCur)) { ::TranslateMessage(&m_msgCur); ::DispatchMessage(&m_msgCur); } return TRUE; } |
因此，忽略IDLE狀態(tài)，整個RUN的執(zhí)行提取主干就是：
| do { ::GetMessage(&msg,...); PreTranslateMessage{&msg); ::TranslateMessage(&msg); ::DispatchMessage(&msg); ... } while (::PeekMessage(...)); |
由此，我們建立了MFC消息獲取和派生機制與WIN32 SDK程序之間的對應關系。下面繼續(xù)分析MFC消息的"繞行"過程。
在MFC中，只要是CWnd衍生類別，就可以攔下任何Windows消息。與窗口無關的MFC類別（例如CDocument和CWinApp）如果也想處理消息，必須衍生自CCmdTarget，并且只可能收到WM_COMMAND消息。所有能進行MESSAGE_MAP的類都繼承自CCmdTarget，如：
   |
MFC中MESSAGE_MAP的定義依賴于以下三個宏：
| DECLARE_MESSAGE_MAP() BEGIN_MESSAGE_MAP( theClass, //Specifies the name of the class whose message map this is baseClass //Specifies the name of the base class of theClass ) END_MESSAGE_MAP() |
我們程序中涉及到的有：MFCThread.h、MainFrm.h、ChildView.h文件
| DECLARE_MESSAGE_MAP() MFCThread.cpp文件 BEGIN_MESSAGE_MAP(CMFCThreadApp, CWinApp) //{{AFX_MSG_MAP(CMFCThreadApp) ON_COMMAND(ID_APP_ABOUT, OnAppAbout) // NOTE - the ClassWizard will add and remove mapping macros here. // DO NOT EDIT what you see in these blocks of generated code! //}}AFX_MSG_MAP END_MESSAGE_MAP() MainFrm.cpp文件 BEGIN_MESSAGE_MAP(CMainFrame, CFrameWnd) //{{AFX_MSG_MAP(CMainFrame) // NOTE - the ClassWizard will add and remove mapping macros here. // DO NOT EDIT what you see in these blocks of generated code ! ON_WM_SETFOCUS() //}}AFX_MSG_MAP END_MESSAGE_MAP() ChildView.cpp文件 BEGIN_MESSAGE_MAP(CChildView,CWnd ) //{{AFX_MSG_MAP(CChildView) ON_WM_PAINT() //}}AFX_MSG_MAP END_MESSAGE_MAP() |
由這些宏，MFC建立了一個消息映射表（消息流動網(wǎng)），按照消息流動網(wǎng)匹配對應的消息處理函數(shù)，完成整個消息的"繞行"。
看到這里相信你有這樣的疑問：程序定義了CWinApp類的theApp全局變量，可是從來沒有調(diào)用AfxBeginThread或theApp.CreateThread啟動線程呀，theApp對應的線程是怎么啟動的？
答：MFC在這里用了很高明的一招。實際上，程序開始運行，第一個線程是由操作系統(tǒng)（OS）啟動的，在CWinApp的構造函數(shù)里，MFC將theApp"對應"向了這個線程，具體的實現(xiàn)是這樣的：
| CWinApp::CWinApp(LPCTSTR lpszAppName) { if (lpszAppName != NULL) m_pszAppName = _tcsdup(lpszAppName); else m_pszAppName = NULL; // initialize CWinThread state AFX_MODULE_STATE *pModuleState = _AFX_CMDTARGET_GETSTATE(); AFX_MODULE_THREAD_STATE *pThreadState = pModuleState->m_thread; ASSERT(AfxGetThread() == NULL); pThreadState->m_pCurrentWinThread = this; ASSERT(AfxGetThread() == this); m_hThread = ::GetCurrentThread(); m_nThreadID = ::GetCurrentThreadId(); // initialize CWinApp state ASSERT(afxCurrentWinApp == NULL); // only one CWinApp object please pModuleState->m_pCurrentWinApp = this; ASSERT(AfxGetApp() == this); // in non-running state until WinMain m_hInstance = NULL; m_pszHelpFilePath = NULL; m_pszProfileName = NULL; m_pszRegistryKey = NULL; m_pszExeName = NULL; m_pRecentFileList = NULL; m_pDocManager = NULL; m_atomApp = m_atomSystemTopic = NULL; //微軟懶鬼？或者他認為 //這樣連等含義更明確？ m_lpCmdLine = NULL; m_pCmdInfo = NULL; // initialize wait cursor state m_nWaitCursorCount = 0; m_hcurWaitCursorRestore = NULL; // initialize current printer state m_hDevMode = NULL; m_hDevNames = NULL; m_nNumPreviewPages = 0; // not specified (defaults to 1) // initialize DAO state m_lpfnDaoTerm = NULL; // will be set if AfxDaoInit called // other initialization m_bHelpMode = FALSE; m_nSafetyPoolSize = 512; // default size } |
很顯然，theApp成員變量都被賦予OS啟動的這個當前線程相關的值，如代碼：
| m_hThread = ::GetCurrentThread();//theApp的線程句柄等于當前線程句柄 m_nThreadID = ::GetCurrentThreadId();//theApp的線程ID等于當前線程ID |
所以CWinApp類幾乎只是為MFC程序的第一個線程量身定制的，它不需要也不能被AfxBeginThread或theApp.CreateThread"再次"啟動。這就是CWinApp類和theApp全局變量的內(nèi)涵！如果你要再增加一個UI線程，不要繼承類CWinApp，而應繼承類CWinThread。而參考第1節(jié)，由于我們一般以主線程（在MFC程序里實際上就是OS啟動的第一個線程）處理所有窗口的消息，所以我們幾乎沒有再啟動UI線程的需求！
