深入浅出Win32多线程设计之MFC的多线程-线程与消息队列(经典)
1、创建和终止线程
在MFC程序中创建一个线程,宜调用AfxBeginThread函数。该函数因参数不同而具有两种重载版本,分别对应工作者线程和用户接口(UI)线程。
工作者线程
CWinThread *AfxBeginThread(
AFX_THREADPROC pfnThreadProc, //控制函数
LPVOID pParam, //传递给控制函数的参数
int nPriority = THREAD_PRIORITY_NORMAL, //线程的优先级
UINT nStackSize = 0, //线程的堆栈大小
DWORD dwCreateFlags = 0, //线程的创建标志
LPSECURITY_ATTRIBUTES lpSecurityAttrs = NULL //线程的安全属性
);
工作者线程编程较为简单,只需编写线程控制函数和启动线程即可。下面的代码给出了定义一个控制函数和启动它的过程:
//线程控制函数
UINT MfcThreadProc(LPVOID lpParam)
{
CExampleClass *lpObject = (CExampleClass*)lpParam;
if (lpObject == NULL || !lpObject->IsKindof(RUNTIME_CLASS(CExampleClass)))
return - 1; //输入参数非法
//线程成功启动
while (1)
{
...//
}
return 0;
}
//在MFC程序中启动线程
AfxBeginThread(MfcThreadProc, lpObject);
UI线程
创建用户界面线程时,必须首先从CWinThread 派生类,并使用 DECLARE_DYNCREATE 和 IMPLEMENT_DYNCREATE 宏声明此类。
下面给出了CWinThread类的原型(添加了关于其重要函数功能和是否需要被继承类重载的注释):
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
//执行线程实例初始化,必须重写
virtual BOOL InitInstance();
// running and idle processing
//控制线程的函数,包含消息泵,一般不重写
virtual int Run();
//消息调度到TranslateMessage和DispatchMessage之前对其进行筛选,
//通常不重写
virtual BOOL PreTranslateMessage(MSG* pMsg);
virtual BOOL PumpMessage(); // low level message pump
//执行线程特定的闲置时间处理,通常不重写
virtual BOOL OnIdle(LONG lCount); // return TRUE if more idle processing
virtual BOOL IsIdleMessage(MSG* pMsg); // checks for special messages
//线程终止时执行清除,通常需要重写
virtual int ExitInstance(); // default will 'delete this'
//截获由线程的消息和命令处理程序引发的未处理异常,通常不重写
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
};
启动UI线程的AfxBeginThread函数的原型为:
CWinThread *AfxBeginThread(
//从CWinThread派生的类的 RUNTIME_CLASS
CRuntimeClass *pThreadClass,
int nPriority = THREAD_PRIORITY_NORMAL,
UINT nStackSize = 0,
DWORD dwCreateFlags = 0,
LPSECURITY_ATTRIBUTES lpSecurityAttrs = NULL
);
我们可以方便地使用VC++ 6.0类向导定义一个继承自CWinThread的用户线程类。下面给出产生我们自定义的CWinThread子类CMyUIThread的方法。
打开VC++ 6.0类向导,在如下窗口中选择Base Class类为CWinThread,输入子类名为CMyUIThread,点击"OK"按钮后就产生了类CMyUIThread。
其源代码框架为:
/////////////////////////////////////////////////////////////////////////////
// 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()
使用下列代码就可以启动这个UI线程:
CMyUIThread *pThread;
pThread = (CMyUIThread*)
AfxBeginThread( RUNTIME_CLASS(CMyUIThread) );
另外,我们也可以不用AfxBeginThread 创建线程,而是分如下两步完成:
(1)调用线程类的构造函数创建一个线程对象;
(2)调用CWinThread::CreateThread函数来启动该线程。
在线程自身内调用AfxEndThread函数可以终止该线程:
void AfxEndThread(
UINT nExitCode //the exit code of the thread
);
对于UI线程而言,如果消息队列中放入了WM_QUIT消息,将结束线程。
关于UI线程和工作者线程的分配,最好的做法是:将所有与UI相关的操作放入主线程,其它的纯粹的运算工作交给独立的数个工作者线程。
候捷先生早些时间喜欢为MDI程序的每个窗口创建一个线程,他后来澄清了这个错误。因为如果为MDI程序的每个窗口都单独创建一个线程,在窗口进行切换的时候,将进行线程的上下文切换!
3.线程与消息队列
在WIN32中,每一个线程都对应着一个消息队列。由于一个线程可以产生数个窗口,所以并不是每个窗口都对应着一个消息队列。下列几句话应该作为"定理"被记住:
"定理" 一
所有产生给某个窗口的消息,都先由创建这个窗口的线程处理;
"定理" 二
Windows屏幕上的每一个控件都是一个窗口,有对应的窗口函数。
消息的发送通常有两种方式,一是SendMessage,一是PostMessage,其原型分别为:
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
);
两个函数原型中的四个参数的意义相同,但是SendMessage和PostMessage的行为有差异。SendMessage必须等待消息被处理后才返回,而PostMessage仅仅将消息放入消息队列。SendMessage的目标窗口如果属于另一个线程,则会发生线程上下文切换,等待另一线程处理完成消息。为了防止另一线程当掉,导致SendMessage永远不能返回,我们可以调用SendMessageTimeout函数:
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线程、消息队列与MFC程序的"生死因果"
分析MFC程序的主线程启动及消息队列处理的过程将有助于我们进一步理解UI线程与消息队列的关系,为此我们需要简单地叙述一下MFC程序的"生死因果"(侯捷:《深入浅出MFC》)。
使用VC++ 6.0的向导完成一个最简单的单文档架构MFC应用程序MFCThread:
(1) 输入MFC EXE工程名MFCThread;
(2) 选择单文档架构,不支持Document/View结构;
(3) ActiveX、3D container等其他选项都选择无。
我们来分析这个工程。下面是产生的核心源代码:
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定义和实现的类CMFCThreadApp继承自CWinApp类,而CWinApp类又继承自CWinThread类(CWinThread类又继承自CCmdTarget类),所以CMFCThread本质上是一个MFC线程类,下图给出了相关的类层次结构:
我们提取CWinApp类原型的一部分:
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 所完成的工作现在由CWinApp 的三个函数完成:
virtual BOOL InitApplication();
virtual BOOL InitInstance();
virtual int Run();
"CMFCThreadApp theApp;"语句定义的全局变量theApp是整个程式的application object,每一个MFC 应用程序都有一个。当我们执行MFCThread程序的时候,这个全局变量被构造。theApp 配置完成后,WinMain开始执行。但是程序中并没有WinMain的代码,它在哪里呢?原来MFC早已准备好并由Linker直接加到应用程序代码中的,其原型为(存在于VC++6.0安装目录下提供的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);
}
其中调用的AfxWinMain如下(存在于VC++6.0安装目录下提供的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;
}
我们提取主干,实际上,这个函数做的事情主要是:
CWinThread* pThread = AfxGetThread();
CWinApp* pApp = AfxGetApp();
AfxWinInit(hInstance, hPrevInstance, lpCmdLine, nCmdShow)
pApp->InitApplication()
pThread->InitInstance()
pThread->Run();
其中,InitApplication 是注册窗口类别的场所;InitInstance是产生窗口并显示窗口的场所;Run是提取并分派消息的场所。这样,MFC就同WIN32 SDK程序对应起来了。CWinThread::Run是程序生命的"活水源头"(侯捷:《深入浅出MFC》,函数存在于VC++ 6.0安装目录下提供的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函数又对应于:
/////////////////////////////////////////////////////////////////////////////
// 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状态,整个RUN的执行提取主干就是:
do {
::GetMessage(&msg,...);
PreTranslateMessage{&msg);
::TranslateMessage(&msg);
::DispatchMessage(&msg);
...
} while (::PeekMessage(...));
由此,我们建立了MFC消息获取和派生机制与WIN32 SDK程序之间的对应关系。下面继续分析MFC消息的"绕行"过程。
在MFC中,只要是CWnd 衍生类别,就可以拦下任何Windows消息。与窗口无关的MFC类别(例如CDocument 和CWinApp)如果也想处理消息,必须衍生自CCmdTarget,并且只可能收到WM_COMMAND消息。所有能进行MESSAGE_MAP的类都继承自CCmdTarget,如:
MFC中MESSAGE_MAP的定义依赖于以下三个宏:
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()
我们程序中涉及到的有: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()
由这些宏,MFC建立了一个消息映射表(消息流动网),按照消息流动网匹配对应的消息处理函数,完成整个消息的"绕行"。
看到这里相信你有这样的疑问:程序定义了CWinApp类的theApp全局变量,可是从来没有调用AfxBeginThread或theApp.CreateThread启动线程呀,theApp对应的线程是怎么启动的?
答:MFC在这里用了很高明的一招。实际上,程序开始运行,第一个线程是由操作系统(OS)启动的,在CWinApp的构造函数里,MFC将theApp"对应"向了这个线程,具体的实现是这样的:
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; //微软懒鬼?或者他认为
//这样连等含义更明确?
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
}
很显然,theApp成员变量都被赋予OS启动的这个当前线程相关的值,如代码:
m_hThread = ::GetCurrentThread();//theApp的线程句柄等于当前线程句柄
m_nThreadID = ::GetCurrentThreadId();//theApp的线程ID等于当前线程ID
所以CWinApp类几乎只是为MFC程序的第一个线程量身定制的,它不需要也不能被AfxBeginThread或theApp.CreateThread"再次"启动。这就是CWinApp类和theApp全局变量的内涵!如果你要再增加一个UI线程,不要继承类CWinApp,而应继承类CWinThread。而参考第1节,由于我们一般以主线程(在MFC程序里实际上就是OS启动的第一个线程)处理所有窗口的消息,所以我们几乎没有再启动UI线程的需求
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