1、建立和終止線程
在MFC程式中建立一個線程,宜調用AfxBeginThread函數。該函數因參數不同而具有兩種重載版本,分别對應工作者線程和使用者接口(UI)線程。
工作者線程
CWinThread *AfxBeginThread(
AFX_THREADPROC pfnThreadProc, //控制函數
LPVOID pParam, //傳遞給控制函數的參數
int nPriority = THREAD_PRIORITY_NORMAL, //線程的優先級
UINT nStackSize = 0, //線程的堆棧大小
DWORD dwCreateFlags = 0, //線程的建立标志
LPSECURITY_ATTRIBUTES lpSecurityAttrs = NULL //線程的安全屬性
);
工作者線程程式設計較為簡單,隻需編寫線程控制函數和啟動線程即可。下面的代碼給出了定義一個控制函數和啟動它的過程:
//線程控制函數
UINT MfcThreadProc(LPVOID lpParam)
{
CExampleClass *lpObject = (CExampleClass*)lpParam;
if (lpObject == NULL || !lpObject->IsKindof(RUNTIME_CLASS(CExampleClass)))
return - 1; //輸入參數非法
//線程成功啟動
while (1)
{
...//
}
return 0;
}
//在MFC程式中啟動線程
AfxBeginThread(MfcThreadProc, lpObject);
UI線程
建立使用者界面線程時,必須首先從CWinThread 派生類,并使用 DECLARE_DYNCREATE 和 IMPLEMENT_DYNCREATE 宏聲明此類。
下面給出了CWinThread類的原型(添加了關于其重要函數功能和是否需要被繼承類重載的注釋):
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
//執行線程執行個體初始化,必須重寫
virtual BOOL InitInstance();
// running and idle processing
//控制線程的函數,包含消息泵,一般不重寫
virtual int Run();
//消息排程到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指令處理程式引發的未處理異常,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
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
// 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
};
啟動UI線程的AfxBeginThread函數的原型為:
//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
);
我們可以友善地使用VC++ 6.0類向導定義一個繼承自CWinThread的使用者線程類。下面給出産生我們自定義的CWinThread子類CMyUIThread的方法。
打開VC++ 6.0類向導,在如下視窗中選擇Base Class類為CWinThread,輸入子類名為CMyUIThread,點選"OK"按鈕後就産生了類CMyUIThread。
其源代碼架構為:
/////////////////////////////////////////////////////////////////////////////
// CMyUIThread thread
class CMyUIThread : public CWinThread
DECLARE_DYNCREATE(CMyUIThread)
CMyUIThread(); // protected constructor used by dynamic creation
// Overrides
// ClassWizard generated virtual function overrides
//{{AFX_VIRTUAL(CMyUIThread)
public:
virtual BOOL InitInstance();
virtual int ExitInstance();
//}}AFX_VIRTUAL
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()
使用下列代碼就可以啟動這個UI線程:
CMyUIThread *pThread;
pThread = (CMyUIThread*)
AfxBeginThread( RUNTIME_CLASS(CMyUIThread) );
另外,我們也可以不用AfxBeginThread 建立線程,而是分如下兩步完成:
(1)調用線程類的構造函數建立一個線程對象;
(2)調用CWinThread::CreateThread函數來啟動該線程。
線上程自身内調用AfxEndThread函數可以終止該線程:
void AfxEndThread(
UINT nExitCode //the exit code of the thread
對于UI線程而言,如果消息隊列中放入了WM_QUIT消息,将結束線程。
關于UI線程和工作者線程的配置設定,最好的做法是:将所有與UI相關的操作放入主線程,其它的純粹的運算工作交給獨立的數個工作者線程。
候捷先生早些時間喜歡為MDI程式的每個視窗建立一個線程,他後來澄清了這個錯誤。因為如果為MDI程式的每個視窗都單獨建立一個線程,在視窗進行切換的時候,将進行線程的上下文切換!
3.線程與消息隊列
在WIN32中,每一個線程都對應着一個消息隊列。由于一個線程可以産生數個視窗,是以并不是每個視窗都對應着一個消息隊列。下列幾句話應該作為"定理"被記住:
"定理" 一
所有産生給某個視窗的消息,都先由建立這個視窗的線程處理;
"定理" 二
Windows螢幕上的每一個控件都是一個視窗,有對應的視窗函數。
消息的發送通常有兩種方式,一是SendMessage,一是PostMessage,其原型分别為:
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
兩個函數原型中的四個參數的意義相同,但是SendMessage和PostMessage的行為有差異。SendMessage必須等待消息被處理後才傳回,而PostMessage僅僅将消息放入消息隊列。SendMessage的目标視窗如果屬于另一個線程,則會發生線程上下文切換,等待另一線程處理完成消息。為了防止另一線程當掉,導緻SendMessage永遠不能傳回,我們可以調用SendMessageTimeout函數:
LRESULT SendMessageTimeout(
HWND hWnd, // handle of destination window
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程式的"生死因果"
分析MFC程式的主線程啟動及消息隊列處理的過程将有助于我們進一步了解UI線程與消息隊列的關系,為此我們需要簡單地叙述一下MFC程式的"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應用程式MFCThread:
(1) 輸入MFC EXE工程名MFCThread;
(2) 選擇單文檔架構,不支援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。下面是産生的核心源代碼:
MFCThread.h 檔案
class CMFCThreadApp : public CWinApp
CMFCThreadApp();
//{{AFX_VIRTUAL(CMFCThreadApp)
public:
virtual BOOL InitInstance();
//{{AFX_MSG(CMFCThreadApp)
afx_msg void OnAppAbout();
// DO NOT EDIT what you see in these blocks of generated code !
MFCThread.cpp檔案
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();
MainFrm.h檔案
#include "ChildView.h"
class CMainFrame : public CFrameWnd
CMainFrame();
protected:
DECLARE_DYNAMIC(CMainFrame)
//{{AFX_VIRTUAL(CMainFrame)
virtual BOOL PreCreateWindow(CREATESTRUCT& cs);
virtual BOOL OnCmdMsg(UINT nID, int nCode, void* pExtra, AFX_CMDHANDLERINFO* pHandlerInfo);
virtual ~CMainFrame();
CChildView m_wndView;
//{{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
MainFrm.cpp檔案
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
// 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);
ChildView.h檔案
// CChildView window
class CChildView : public CWnd
// Construction
CChildView();
//{{AFX_VIRTUAL(CChildView)
protected:
virtual BOOL PreCreateWindow(CREATESTRUCT& cs);
virtual ~CChildView();
//{{AFX_MSG(CChildView)
afx_msg void OnPaint();
ChildView.cpp檔案
// CChildView
CChildView::CChildView()
CChildView::~CChildView()
BEGIN_MESSAGE_MAP(CChildView,CWnd )
//{{AFX_MSG_MAP(CChildView)
ON_WM_PAINT()
// CChildView message handlers
BOOL CChildView::PreCreateWindow(CREATESTRUCT& cs)
if (!CWnd::PreCreateWindow(cs))
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);
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
檔案MFCThread.h和MFCThread.cpp定義和實作的類CMFCThreadApp繼承自CWinApp類,而CWinApp類又繼承自CWinThread類(CWinThread類又繼承自CCmdTarget類),是以CMFCThread本質上是一個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)
// Constructor
CWinApp(LPCTSTR lpszAppName = NULL);// default app name
// 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
virtual BOOL InitApplication();
virtual int ExitInstance(); // return app exit code
virtual LRESULT ProcessWndProcException(CException* e,const MSG* pMsg);
virtual ~CWinApp();
DECLARE_MESSAGE_MAP()
SDK程式的WinMain 所完成的工作現在由CWinApp 的三個函數完成:
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application object,每一個MFC 應用程式都有一個。當我們執行MFCThread程式的時候,這個全局變量被構造。theApp 配置完成後,WinMain開始執行。但是程式中并沒有WinMain的代碼,它在哪裡呢?原來MFC早已準備好并由Linker直接加到應用程式代碼中的,其原型為(存在于VC++6.0安裝目錄下提供的APPMODUL.CPP檔案中):
extern "C" int WINAPI
_tWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
LPTSTR lpCmdLine, int nCmdShow)
// call shared/exported WinMain
return AfxWinMain(hInstance, hPrevInstance, lpCmdLine, nCmdShow);
其中調用的AfxWinMain如下(存在于VC++6.0安裝目錄下提供的WINMAIN.CPP檔案中):
int AFXAPI AfxWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
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())
// 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();
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;
我們提取主幹,實際上,這個函數做的事情主要是:
CWinThread* pThread = AfxGetThread();
CWinApp* pApp = AfxGetApp();
AfxWinInit(hInstance, hPrevInstance, lpCmdLine, nCmdShow)
pApp->InitApplication()
pThread->InitInstance()
pThread->Run();
其中,InitApplication 是注冊視窗類别的場所;InitInstance是産生視窗并顯示視窗的場所;Run是提取并分派消息的場所。這樣,MFC就同WIN32 SDK程式對應起來了。CWinThread::Run是程式生命的"活水源頭"(侯捷:《深入淺出MFC》,函數存在于VC++ 6.0安裝目錄下提供的THRDCORE.CPP檔案中):
// 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函數又對應于:
// CWinThread implementation helpers
BOOL CWinThread::PumpMessage()
if (!::GetMessage(&m_msgCur, NULL, NULL, NULL))
// process this message
if(m_msgCur.message != WM_KICKIDLE && !PreTranslateMessage(&m_msgCur))
::TranslateMessage(&m_msgCur);
::DispatchMessage(&m_msgCur);
是以,忽略IDLE狀态,整個RUN的執行提取主幹就是:
do {
::GetMessage(&msg,...);
PreTranslateMessage{&msg);
::TranslateMessage(&msg);
::DispatchMessage(&msg);
...
} while (::PeekMessage(...));
由此,我們建立了MFC消息擷取和派生機制與WIN32 SDK程式之間的對應關系。下面繼續分析MFC消息的"繞行"過程。
在MFC中,隻要是CWnd 衍生類别,就可以攔下任何Windows消息。與視窗無關的MFC類别(例如CDocument 和CWinApp)如果也想處理消息,必須衍生自CCmdTarget,并且隻可能收到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
)
我們程式中涉及到的有:MFCThread.h、MainFrm.h、ChildView.h檔案
MFCThread.cpp檔案
BEGIN_MESSAGE_MAP(CMFCThreadApp, CWinApp)
//{{AFX_MSG_MAP(CMFCThreadApp)
ON_COMMAND(ID_APP_ABOUT, OnAppAbout)
// DO NOT EDIT what you see in these blocks of generated code!
MainFrm.cpp檔案
//{{AFX_MSG_MAP(CMainFrame)
// DO NOT EDIT what you see in these blocks of generated code !
ON_WM_SETFOCUS()
由這些宏,MFC建立了一個消息映射表(消息流動網),按照消息流動網比對對應的消息處理函數,完成整個消息的"繞行"。
看到這裡相信你有這樣的疑問:程式定義了CWinApp類的theApp全局變量,可是從來沒有調用AfxBeginThread或theApp.CreateThread啟動線程呀,theApp對應的線程是怎麼啟動的?
答:MFC在這裡用了很高明的一招。實際上,程式開始運作,第一個線程是由作業系統(OS)啟動的,在CWinApp的構造函數裡,MFC将theApp"對應"向了這個線程,具體的實作是這樣的:
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
//這樣連等含義更明确?
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啟動的這個目前線程相關的值,如代碼:
m_hThread = ::GetCurrentThread();//theApp的線程句柄等于目前線程句柄
m_nThreadID = ::GetCurrentThreadId();//theApp的線程ID等于目前線程ID
是以CWinApp類幾乎隻是為MFC程式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全局變量的内涵!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,由于我們一般以主線程(在MFC程式裡實際上就是OS啟動的第一個線程)處理所有視窗的消息,是以我們幾乎沒有再啟動UI線程的需求