MFC的多线程
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1、创建和终止线程
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。
其源代码框架为:
打开VC++6.0类向导,在如下窗口中选择BaseClass类为CWinThread,输入子类名为CMyUIThread,点击"OK"按钮后就产生了类CMyUIThread。/////////////////////////////////////////////////////////////////////////////// CMyUIThread threadclass 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()};/////////////////////////////////////////////////////////////////////////////// CMyUIThreadIMPLEMENT_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_MAPEND_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!
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