信號量
信號量是維護0到指定最大值之間的同步對象。信號量狀態(tài)在其計數大于0時(shí)是有信號的，而其計數是0時(shí)是無(wú)信號的。信號量對象在控制上可以支持有限數量共享資源的訪(fǎng)問(wèn)。
信號量的特點(diǎn)和用途可用下列幾句話(huà)定義：
?。?）如果當前資源的數量大于0，則信號量有效；
?。?）如果當前資源數量是0，則信號量無(wú)效；
?。?）系統決不允許當前資源的數量為負值；
?。?）當前資源數量決不能大于最大資源數量。
創(chuàng )建信號量
HANDLE CreateSemaphore (
PSECURITY_ATTRIBUTE psa,
LONG lInitialCount, //開(kāi)始時(shí)可供使用的資源數
LONG lMaximumCount, //最大資源數
PCTSTR pszName); |
釋放信號量
通過(guò)調用ReleaseSemaphore函數，線(xiàn)程就能夠對信標的當前資源數量進(jìn)行遞增，該函數原型為：
BOOL WINAPI ReleaseSemaphore(
HANDLE hSemaphore,
LONG lReleaseCount, //信號量的當前資源數增加lReleaseCount
LPLONG lpPreviousCount
); |
打開(kāi)信號量
和其他核心對象一樣，信號量也可以通過(guò)名字跨進(jìn)程訪(fǎng)問(wèn)，打開(kāi)信號量的API為：
HANDLE OpenSemaphore (
DWORD fdwAccess,
BOOL bInherithandle,
PCTSTR pszName
); |
互鎖訪(fǎng)問(wèn)
當必須以原子操作方式來(lái)修改單個(gè)值時(shí)，互鎖訪(fǎng)問(wèn)函數是相當有用的。所謂原子訪(fǎng)問(wèn)，是指線(xiàn)程在訪(fǎng)問(wèn)資源時(shí)能夠確保所有其他線(xiàn)程都不在同一時(shí)間內訪(fǎng)問(wèn)相同的資源。
請看下列代碼：
int globalVar = 0;
DWORD WINAPI ThreadFunc1(LPVOID n)
{
globalVar++;
return 0;
}
DWORD WINAPI ThreadFunc2(LPVOID n)
{
globalVar++;
return 0;
} |
運行ThreadFunc1和ThreadFunc2線(xiàn)程，結果是不可預料的，因為globalVar++并不對應著(zhù)一條機器指令，我們看看globalVar++的反匯編代碼：
00401038 mov eax,[globalVar (0042d3f0)]
0040103D add eax,1
00401040 mov [globalVar (0042d3f0)],eax |
在"mov eax,[globalVar (0042d3f0)]" 指令與"add eax,1" 指令以及"add eax,1" 指令與"mov [globalVar (0042d3f0)],eax"指令之間都可能發(fā)生線(xiàn)程切換，使得程序的執行后globalVar的結果不能確定。我們可以使用InterlockedExchangeAdd函數解決這個(gè)問(wèn)題：
int globalVar = 0;
DWORD WINAPI ThreadFunc1(LPVOID n)
{
InterlockedExchangeAdd(&globalVar,1);
return 0;
}
DWORD WINAPI ThreadFunc2(LPVOID n)
{
InterlockedExchangeAdd(&globalVar,1);
return 0;
} |
InterlockedExchangeAdd保證對變量globalVar的訪(fǎng)問(wèn)具有"原子性"?；ユi訪(fǎng)問(wèn)的控制速度非?？?，調用一個(gè)互鎖函數的CPU周期通常小于50，不需要進(jìn)行用戶(hù)方式與內核方式的切換（該切換通常需要運行1000個(gè)CPU周期）。
互鎖訪(fǎng)問(wèn)函數的缺點(diǎn)在于其只能對單一變量進(jìn)行原子訪(fǎng)問(wèn)，如果要訪(fǎng)問(wèn)的資源比較復雜，仍要使用臨界區或互斥。
可等待定時(shí)器
可等待定時(shí)器是在某個(gè)時(shí)間或按規定的間隔時(shí)間發(fā)出自己的信號通知的內核對象。它們通常用來(lái)在某個(gè)時(shí)間執行某個(gè)操作。
創(chuàng )建可等待定時(shí)器
HANDLE CreateWaitableTimer(
PSECURITY_ATTRISUTES psa,
BOOL fManualReset,//人工重置或自動(dòng)重置定時(shí)器
PCTSTR pszName); |
設置可等待定時(shí)器
可等待定時(shí)器對象在非激活狀態(tài)下被創(chuàng )建，程序員應調用 SetWaitableTimer函數來(lái)界定定時(shí)器在何時(shí)被激活：
BOOL SetWaitableTimer(
HANDLE hTimer, //要設置的定時(shí)器
const LARGE_INTEGER *pDueTime, //指明定時(shí)器第一次激活的時(shí)間
LONG lPeriod, //指明此后定時(shí)器應該間隔多長(cháng)時(shí)間激活一次
PTIMERAPCROUTINE pfnCompletionRoutine,
PVOID PvArgToCompletionRoutine,
BOOL fResume); |
取消可等待定時(shí)器
BOOl Cancel WaitableTimer(
HANDLE hTimer //要取消的定時(shí)器
); |
打開(kāi)可等待定時(shí)器
作為一種內核對象，WaitableTimer也可以被其他進(jìn)程以名字打開(kāi)：
HANDLE OpenWaitableTimer (
DWORD fdwAccess,
BOOL bInherithandle,
PCTSTR pszName
); |
實(shí)例
下面給出的一個(gè)程序可能發(fā)生死鎖現象：
#include <windows.h>
#include <stdio.h>
CRITICAL_SECTION cs1, cs2;
long WINAPI ThreadFn(long);
main()
{
long iThreadID;
InitializeCriticalSection(&cs1);
InitializeCriticalSection(&cs2);
CloseHandle(CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)ThreadFn, NULL, 0,&iThreadID));
while (TRUE)
{
EnterCriticalSection(&cs1);
printf("\n線(xiàn)程1占用臨界區1");
EnterCriticalSection(&cs2);
printf("\n線(xiàn)程1占用臨界區2");
printf("\n線(xiàn)程1占用兩個(gè)臨界區");
LeaveCriticalSection(&cs2);
LeaveCriticalSection(&cs1);
printf("\n線(xiàn)程1釋放兩個(gè)臨界區");
Sleep(20);
};
return (0);
}
long WINAPI ThreadFn(long lParam)
{
while (TRUE)
{
EnterCriticalSection(&cs2);
printf("\n線(xiàn)程2占用臨界區2");
EnterCriticalSection(&cs1);
printf("\n線(xiàn)程2占用臨界區1");
printf("\n線(xiàn)程2占用兩個(gè)臨界區");
LeaveCriticalSection(&cs1);
LeaveCriticalSection(&cs2);
printf("\n線(xiàn)程2釋放兩個(gè)臨界區");
Sleep(20);
};
} |
運行這個(gè)程序，在中途一旦發(fā)生這樣的輸出：
線(xiàn)程1占用臨界區1
線(xiàn)程2占用臨界區2
或
線(xiàn)程2占用臨界區2
線(xiàn)程1占用臨界區1
或
線(xiàn)程1占用臨界區2
線(xiàn)程2占用臨界區1
或
線(xiàn)程2占用臨界區1
線(xiàn)程1占用臨界區2
程序就"死"掉了，再也運行不下去。因為這樣的輸出，意味著(zhù)兩個(gè)線(xiàn)程相互等待對方釋放臨界區，也即出現了死鎖。
如果我們將線(xiàn)程2的控制函數改為：
long WINAPI ThreadFn(long lParam)
{
while (TRUE)
{
EnterCriticalSection(&cs1);
printf("\n線(xiàn)程2占用臨界區1");
EnterCriticalSection(&cs2);
printf("\n線(xiàn)程2占用臨界區2");
printf("\n線(xiàn)程2占用兩個(gè)臨界區");
LeaveCriticalSection(&cs1);
LeaveCriticalSection(&cs2);
printf("\n線(xiàn)程2釋放兩個(gè)臨界區");
Sleep(20);
};
} |
再次運行程序，死鎖被消除，程序不再擋掉。這是因為我們改變了線(xiàn)程2中獲得臨界區1、2的順序，消除了線(xiàn)程1、2相互等待資源的可能性。
由此我們得出結論，在使用線(xiàn)程間的同步機制時(shí)，要特別留心死鎖的發(fā)生。 深入淺出Win32多線(xiàn)程設計之MFC的多線(xiàn)程 1、創(chuàng )建和終止線(xiàn)程 在MFC程序中創(chuàng )建一個(gè)線(xiàn)程，宜調用AfxBeginThread函數。該函數因參數不同而具有兩種重載版本，分別對應工作者線(xiàn)程和用戶(hù)接口（UI）線(xiàn)程。 工作者線(xiàn)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(xiàn)程的優(yōu)先級
UINT nStackSize = 0, //線(xiàn)程的堆棧大小
DWORD dwCreateFlags = 0, //線(xiàn)程的創(chuàng )建標志
LPSECURITY_ATTRIBUTES lpSecurityAttrs = NULL //線(xiàn)程的安全屬性
); |
工作者線(xiàn)程編程較為簡(jiǎn)單，只需編寫(xiě)線(xiàn)程控制函數和啟動(dòng)線(xiàn)程即可。下面的代碼給出了定義一個(gè)控制函數和啟動(dòng)它的過(guò)程： //線(xiàn)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(xiàn)程成功啟動(dòng)
while (1)
{
...//
}
return 0;
}
//在MFC程序中啟動(dòng)線(xiàn)程
AfxBeginThread(MfcThreadProc, lpObject); |
UI線(xiàn)程 創(chuàng )建用戶(hù)界面線(xiàn)程時(shí)，必須首先從CWinThread 派生類(lèi)，并使用 DECLARE_DYNCREATE 和 IMPLEMENT_DYNCREATE 宏聲明此類(lèi)。 下面給出了CWinThread類(lèi)的原型（添加了關(guān)于其重要函數功能和是否需要被繼承類(lèi)重載的注釋?zhuān)?br> 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(xiàn)程實(shí)例初始化，必須重寫(xiě)
virtual BOOL InitInstance();
// running and idle processing
//控制線(xiàn)程的函數，包含消息泵，一般不重寫(xiě)
virtual int Run();
//消息調度到TranslateMessage和DispatchMessage之前對其進(jìn)行篩選，
//通常不重寫(xiě)
virtual BOOL PreTranslateMessage(MSG* pMsg);
virtual BOOL PumpMessage(); // low level message pump
//執行線(xiàn)程特定的閑置時(shí)間處理，通常不重寫(xiě)
virtual BOOL OnIdle(LONG lCount); // return TRUE if more idle processing
virtual BOOL IsIdleMessage(MSG* pMsg); // checks for special messages
//線(xiàn)程終止時(shí)執行清除，通常需要重寫(xiě)
virtual int ExitInstance(); // default will 'delete this'
//截獲由線(xiàn)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(xiě)
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
};
|
啟動(dòng)UI線(xiàn)程的AfxBeginThread函數的原型為： CWinThread *AfxBeginThread(
//從CWinThread派生的類(lèi)的 RUNTIME_CLASS
CRuntimeClass *pThreadClass,
int nPriority = THREAD_PRIORITY_NORMAL,
UINT nStackSize = 0,
DWORD dwCreateFlags = 0,
LPSECURITY_ATTRIBUTES lpSecurityAttrs = NULL
); |
我們可以方便地使用VC++ 6.0類(lèi)向導定義一個(gè)繼承自CWinThread的用戶(hù)線(xiàn)程類(lèi)。下面給出產(chǎn)生我們自定義的CWinThread子類(lèi)CMyUIThread的方法。 打開(kāi)VC++ 6.0類(lèi)向導，在如下窗口中選擇Base Class類(lèi)為CWinThread，輸入子類(lèi)名為CMyUIThread，點(diǎn)擊"OK"按鈕后就產(chǎn)生了類(lèi)CMyUIThread。 其源代碼框架為： /////////////////////////////////////////////////////////////////////////////
// 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() |
使用下列代碼就可以啟動(dòng)這個(gè)UI線(xiàn)程： CMyUIThread *pThread;
pThread = (CMyUIThread*)
AfxBeginThread( RUNTIME_CLASS(CMyUIThread) ); |
另外，我們也可以不用AfxBeginThread 創(chuàng )建線(xiàn)程，而是分如下兩步完成： ?。?）調用線(xiàn)程類(lèi)的構造函數創(chuàng )建一個(gè)線(xiàn)程對象； ?。?）調用CWinThread::CreateThread函數來(lái)啟動(dòng)該線(xiàn)程。 在線(xiàn)程自身內調用AfxEndThread函數可以終止該線(xiàn)程： void AfxEndThread(
UINT nExitCode //the exit code of the thread
); |
對于UI線(xiàn)程而言，如果消息隊列中放入了WM_QUIT消息，將結束線(xiàn)程。 關(guān)于UI線(xiàn)程和工作者線(xiàn)程的分配，最好的做法是：將所有與UI相關(guān)的操作放入主線(xiàn)程，其它的純粹的運算工作交給獨立的數個(gè)工作者線(xiàn)程。 候捷先生早些時(shí)間喜歡為MDI程序的每個(gè)窗口創(chuàng )建一個(gè)線(xiàn)程，他后來(lái)澄清了這個(gè)錯誤。因為如果為MDI程序的每個(gè)窗口都單獨創(chuàng )建一個(gè)線(xiàn)程，在窗口進(jìn)行切換的時(shí)候，將進(jìn)行線(xiàn)程的上下文切換！ 2.線(xiàn)程間通信 MFC中定義了繼承自CSyncObject類(lèi)的CCriticalSection 、CCEvent、CMutex、CSemaphore類(lèi)封裝和簡(jiǎn)化了WIN32 API所提供的臨界區、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(lèi)的繼承關(guān)系： 作為CSyncObject類(lèi)的繼承類(lèi)，我們僅僅使用基類(lèi)CSyncObject的接口函數就可以方便、統一的操作CCriticalSection 、CCEvent、CMutex、CSemaphore類(lèi)，下面是CSyncObject類(lèi)的原型： 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;
}; |
CSyncObject類(lèi)最主要的兩個(gè)函數是Lock和Unlock，若我們直接使用CSyncObject類(lèi)及其派生類(lèi)，我們需要非常小心地在Lock之后調用Unlock。 MFC提供的另兩個(gè)類(lèi)CSingleLock（等待一個(gè)對象）和CMultiLock（等待多個(gè)對象）為我們編寫(xiě)應用程序提供了更靈活的機制，下面以實(shí)際來(lái)闡述CSingleLock的用法： 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
}
} |
上述實(shí)例講述了用CSingleLock對Windows GDI相關(guān)對象進(jìn)行保護的方法，下面再給出一個(gè)其他方面的例子： int array1[10], array2[10];
CMutexSection section; //創(chuàng )建一個(gè)CMutex類(lèi)的對象
//賦值線(xiàn)程控制函數
UINT EvaluateThread(LPVOID param)
{
CSingleLock singlelock;
singlelock(§ion);
//互斥區域
singlelock.Lock();
for (int i = 0; i < 10; i++)
array1[i] = i;
singlelock.Unlock();
}
//拷貝線(xiàn)程控制函數
UINT CopyThread(LPVOID param)
{
CSingleLock singlelock;
singlelock(§ion);
//互斥區域
singlelock.Lock();
for (int i = 0; i < 10; i++)
array2[i] = array1[i];
singlelock.Unlock();
}
}
AfxBeginThread(EvaluateThread, NULL); //啟動(dòng)賦值線(xiàn)程
AfxBeginThread(CopyThread, NULL); //啟動(dòng)拷貝線(xiàn)程 |
上面的例子中啟動(dòng)了兩個(gè)線(xiàn)程EvaluateThread和CopyThread，線(xiàn)程EvaluateThread把10個(gè)數賦值給數組array1[]，線(xiàn)程CopyThread將數組array1[]拷貝給數組array2[]。由于數組的拷貝和賦值都是整體行為，如果不以互斥形式執行代碼段： for (int i = 0; i < 10; i++)
array1[i] = i; |
和 for (int i = 0; i < 10; i++)
array2[i] = array1[i]; |
其結果是很難預料的！ 除了可使用CCriticalSection、CEvent、CMutex、CSemaphore作為線(xiàn)程間同步通信的方式以外，我們還可以利用PostThreadMessage函數在線(xiàn)程間發(fā)送消息： BOOL PostThreadMessage(DWORD idThread, // thread identifier
UINT Msg, // message to post
WPARAM wParam, // first message parameter
LPARAM lParam // second message parameter
); |
3.線(xiàn)程與消息隊列 在WIN32中，每一個(gè)線(xiàn)程都對應著(zhù)一個(gè)消息隊列。由于一個(gè)線(xiàn)程可以產(chǎn)生數個(gè)窗口，所以并不是每個(gè)窗口都對應著(zhù)一個(gè)消息隊列。下列幾句話(huà)應該作為"定理"被記?。?br> "定理" 一 所有產(chǎn)生給某個(gè)窗口的消息，都先由創(chuàng )建這個(gè)窗口的線(xiàn)程處理； "定理" 二 Windows屏幕上的每一個(gè)控件都是一個(gè)窗口，有對應的窗口函數。 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(gè)函數原型中的四個(gè)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(gè)線(xiàn)程，則會(huì )發(fā)生線(xiàn)程上下文切換，等待另一線(xiàn)程處理完成消息。為了防止另一線(xiàn)程當掉，導致SendMessage永遠不能返回，我們可以調用SendMessageTimeout函數： 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(xiàn)程、消息隊列與MFC程序的"生死因果" 分析MFC程序的主線(xiàn)程啟動(dòng)及消息隊列處理的過(guò)程將有助于我們進(jìn)一步理解UI線(xiàn)程與消息隊列的關(guān)系，為此我們需要簡(jiǎn)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(gè)最簡(jiǎn)單的單文檔架構MFC應用程序MFCThread： ?。?） 輸入MFC EXE工程名MFCThread； ?。?） 選擇單文檔架構，不支持Document/View結構； ?。?） ActiveX、3D container等其他選項都選擇無(wú)。 我們來(lái)分析這個(gè)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(shí)現的類(lèi)CMFCThreadApp繼承自CWinApp類(lèi)，而CWinApp類(lèi)又繼承自CWinThread類(lèi)（CWinThread類(lèi)又繼承自CCmdTarget類(lèi)），所以CMFCThread本質(zhì)上是一個(gè)MFC線(xiàn)程類(lèi)，下圖給出了相關(guān)的類(lèi)層次結構： 我們提取CWinApp類(lèi)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 所完成的工作現在由CWinApp 的三個(gè)函數完成： virtual BOOL InitApplication();
virtual BOOL InitInstance();
virtual int Run(); |
"CMFCThreadApp theApp;"語(yǔ)句定義的全局變量theApp是整個(gè)程式的application object，每一個(gè)MFC 應用程序都有一個(gè)。當我們執行MFCThread程序的時(shí)候，這個(gè)全局變量被構造。theApp 配置完成后，WinMain開(kāi)始執行。但是程序中并沒(méi)有WinMain的代碼，它在哪里呢？原來(lái)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(shí)際上，這個(gè)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 是注冊窗口類(lèi)別的場(chǎng)所；InitInstance是產(chǎn)生窗口并顯示窗口的場(chǎng)所；Run是提取并分派消息的場(chǎng)所。這樣，MFC就同WIN32 SDK程序對應起來(lái)了。CWinThread::Run是程序生命的"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(gè)RUN的執行提取主干就是： 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(guān)系。下面繼續分析MFC消息的"繞行"過(guò)程。 在MFC中，只要是CWnd 衍生類(lèi)別，就可以攔下任何Windows消息。與窗口無(wú)關(guān)的MFC類(lèi)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(jìn)行MESSAGE_MAP的類(lèi)都繼承自CCmdTarget，如： MFC中MESSAGE_MAP的定義依賴(lài)于以下三個(gè)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(gè)消息映射表（消息流動(dòng)網(wǎng)），按照消息流動(dòng)網(wǎng)匹配對應的消息處理函數，完成整個(gè)消息的"繞行"。 看到這里相信你有這樣的疑問(wèn)：程序定義了CWinApp類(lèi)的theApp全局變量，可是從來(lái)沒(méi)有調用AfxBeginThread或theApp.CreateThread啟動(dòng)線(xiàn)程呀，theApp對應的線(xiàn)程是怎么啟動(dòng)的？ 答：MFC在這里用了很高明的一招。實(shí)際上，程序開(kāi)始運行，第一個(gè)線(xiàn)程是由操作系統（OS）啟動(dòng)的，在CWinApp的構造函數里，MFC將theApp"對應"向了這個(gè)線(xiàn)程，具體的實(shí)現是這樣的： 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(dòng)的這個(gè)當前線(xiàn)程相關(guān)的值，如代碼： m_hThread = ::GetCurrentThread();//theApp的線(xiàn)程句柄等于當前線(xiàn)程句柄
m_nThreadID = ::GetCurrentThreadId();//theApp的線(xiàn)程ID等于當前線(xiàn)程ID |
所以CWinApp類(lèi)幾乎只是為MFC程序的第一個(gè)線(xiàn)程量身定制的，它不需要也不能被AfxBeginThread或theApp.CreateThread"再次"啟動(dòng)。這就是CWinApp類(lèi)和theApp全局變量的內涵！如果你要再增加一個(gè)UI線(xiàn)程，不要繼承類(lèi)CWinApp，而應繼承類(lèi)CWinThread。而參考第1節，由于我們一般以主線(xiàn)程（在MFC程序里實(shí)際上就是OS啟動(dòng)的第一個(gè)線(xiàn)程）處理所有窗口的消息，所以我們幾乎沒(méi)有再啟動(dòng)UI線(xiàn)程的需求！ 深入淺出Win32多線(xiàn)程程序設計之綜合實(shí)例 本章我們將以工業(yè)控制和嵌入式系統中運用極為廣泛的串口通信為例講述多線(xiàn)程的典型應用。
而網(wǎng)絡(luò )通信也是多線(xiàn)程應用最廣泛的領(lǐng)域之一，所以本章的最后一節也將對多線(xiàn)程網(wǎng)絡(luò )通信進(jìn)行簡(jiǎn)短的描述。
1.串口通信
在工業(yè)控制系統中，工控機（一般都基于PC Windows平臺）經(jīng)常需要與單片機通過(guò)串口進(jìn)行通信。因此，操作和使用PC的串口成為大多數單片機、嵌入式系統領(lǐng)域工程師必須具備的能力。
串口的使用需要通過(guò)三個(gè)步驟來(lái)完成的：
?。?） 打開(kāi)通信端口；
?。?） 初始化串口，設置波特率、數據位、停止位、奇偶校驗等參數。為了給讀者一個(gè)直觀(guān)的印象，下圖從Windows的"控制面板－>系統－>設備管理器－>通信端口（COM1）"打開(kāi)COM的設置窗口：
?。?） 讀寫(xiě)串口。
在WIN32平臺下，對通信端口進(jìn)行操作跟基本的文件操作一樣。
創(chuàng )建/打開(kāi)COM資源
下列函數如果調用成功，則返回一個(gè)標識通信端口的句柄，否則返回-1：
HADLE CreateFile(PCTSTR lpFileName, //通信端口名，如"COM1"
WORD dwDesiredAccess, //對資源的訪(fǎng)問(wèn)類(lèi)型
WORD dwShareMode, //指定共享模式，COM不能共享，該參數為0
PSECURITY_ATTRIBUTES lpSecurityAttributes,
//安全描述符指針，可為NULL
WORD dwCreationDisposition, //創(chuàng )建方式
WORD dwFlagsAndAttributes, //文件屬性，可為NULL
HANDLE hTemplateFile //模板文件句柄，置為NULL
); |
獲得/設置COM屬性
下列函數可以獲得COM口的設備控制塊，從而獲得相關(guān)參數：
BOOL WINAPI GetCommState(
HANDLE hFile, //標識通信端口的句柄
LPDCB lpDCB //指向一個(gè)設備控制塊(DCB結構)的指針
); |
如果要調整通信端口的參數，則需要重新配置設備控制塊，再用WIN32 API SetCommState()函數進(jìn)行設置：
BOOL SetCommState(
HANDLE hFile, //標識通信端口的句柄
LPDCB lpDCB //指向一個(gè)設備控制塊(DCB結構)的指針
); |
DCB結構包含了串口的各項參數設置，如下：
typedef struct _DCB
{
// dcb
DWORD DCBlength; // sizeof(DCB)
DWORD BaudRate; // current baud rate
DWORD fBinary: 1; // binary mode, no EOF check
DWORD fParity: 1; // enable parity checking
DWORD fOutxCtsFlow: 1; // CTS output flow control
DWORD fOutxDsrFlow: 1; // DSR output flow control
DWORD fDtrControl: 2; // DTR flow control type
DWORD fDsrSensitivity: 1; // DSR sensitivity
DWORD fTXContinueOnXoff: 1; // XOFF continues Tx
DWORD fOutX: 1; // XON/XOFF out flow control
DWORD fInX: 1; // XON/XOFF in flow control
DWORD fErrorChar: 1; // enable error replacement
DWORD fNull: 1; // enable null stripping
DWORD fRtsControl: 2; // RTS flow control
DWORD fAbortOnError: 1; // abort reads/writes on error
DWORD fDummy2: 17; // reserved
WORD wReserved; // not currently used
WORD XonLim; // transmit XON threshold
WORD XoffLim; // transmit XOFF threshold
BYTE ByteSize; // number of bits/byte, 4-8
BYTE Parity; // 0-4=no,odd,even,mark,space
BYTE StopBits; // 0,1,2 = 1, 1.5, 2
char XonChar; // Tx and Rx XON character
char XoffChar; // Tx and Rx XOFF character
char ErrorChar; // error replacement character
char EofChar; // end of input character
char EvtChar; // received event character
WORD wReserved1; // reserved; do not use
} DCB; |
讀寫(xiě)串口
在讀寫(xiě)串口之前，還要用PurgeComm()函數清空緩沖區，并用SetCommMask ()函數設置事件掩模來(lái)監視指定通信端口上的事件，其原型為：
BOOL SetCommMask(
HANDLE hFile, //標識通信端口的句柄
DWORD dwEvtMask //能夠使能的通信事件
); |
串口上可能發(fā)生的事件如下表所示：
| 值 | 事件描述 | | EV_BREAK | A break was detected on input. | | EV_CTS | The CTS (clear-to-send) signal changed state. | | EV_DSR | The DSR(data-set-ready) signal changed state. | | EV_ERR | A line-status error occurred. Line-status errors are CE_FRAME, CE_OVERRUN, and CE_RXPARITY. | | EV_RING | A ring indicator was detected. | | EV_RLSD | The RLSD (receive-line-signal-detect) signal changed state. | | EV_RXCHAR | A character was received and placed in the input buffer. | | EV_RXFLAG | The event character was received and placed in the input buffer. The event character is specified in the device's DCB structure, which is applied to a serial port by using the SetCommState function. | | EV_TXEMPTY | The last character in the output buffer was sent. |
在設置好事件掩模后，我們就可以利用WaitCommEvent()函數來(lái)等待串口上發(fā)生事件，其函數原型為：
BOOL WaitCommEvent(
HANDLE hFile, //標識通信端口的句柄
LPDWORD lpEvtMask, //指向存放事件標識變量的指針
LPOVERLAPPED lpOverlapped, // 指向overlapped結構
); |
我們可以在發(fā)生事件后，根據相應的事件類(lèi)型，進(jìn)行串口的讀寫(xiě)操作：
BOOL ReadFile(HANDLE hFile, //標識通信端口的句柄
LPVOID lpBuffer, //輸入數據Buffer指針
DWORD nNumberOfBytesToRead, // 需要讀取的字節數
LPDWORD lpNumberOfBytesRead, //實(shí)際讀取的字節數指針
LPOVERLAPPED lpOverlapped //指向overlapped結構
);
BOOL WriteFile(HANDLE hFile, //標識通信端口的句柄
LPCVOID lpBuffer, //輸出數據Buffer指針
DWORD nNumberOfBytesToWrite, //需要寫(xiě)的字節數
LPDWORD lpNumberOfBytesWritten, //實(shí)際寫(xiě)入的字節數指針
LPOVERLAPPED lpOverlapped //指向overlapped結構
); |
2.工程實(shí)例
下面我們用第1節所述API實(shí)現一個(gè)多線(xiàn)程的串口通信程序。這個(gè)例子工程（工程名為MultiThreadCom）的界面很簡(jiǎn)單，如下圖所示：
它是一個(gè)多線(xiàn)程的應用程序，包括兩個(gè)工作者線(xiàn)程，分別處理串口1和串口2。為了簡(jiǎn)化問(wèn)題，我們讓連接兩個(gè)串口的電纜只包含RX、TX兩根連線(xiàn)（即不以硬件控制RS-232，串口上只會(huì )發(fā)生EV_TXEMPTY、EV_RXCHAR事件）。
在工程實(shí)例的BOOL CMultiThreadComApp::InitInstance()函數中，啟動(dòng)并設置COM1和COM2，其源代碼為：
BOOL CMultiThreadComApp::InitInstance()
{
AfxEnableControlContainer();
//打開(kāi)并設置COM1
hComm1=CreateFile("COM1", GENERIC_READ|GENERIC_WRITE, 0, NULL ,OPEN_EXISTING, 0,NULL);
if (hComm1==(HANDLE)-1)
{
AfxMessageBox("打開(kāi)COM1失敗");
return false;
}
else
{
DCB wdcb;
GetCommState (hComm1,&wdcb);
wdcb.BaudRate=9600;
SetCommState (hComm1,&wdcb);
PurgeComm(hComm1,PURGE_TXCLEAR);
}
//打開(kāi)并設置COM2
hComm2=CreateFile("COM2", GENERIC_READ|GENERIC_WRITE, 0, NULL ,OPEN_EXISTING, 0,NULL);
if (hComm2==(HANDLE)-1)
{
AfxMessageBox("打開(kāi)COM2失敗");
return false;
}
else
{
DCB wdcb;
GetCommState (hComm2,&wdcb);
wdcb.BaudRate=9600;
SetCommState (hComm2,&wdcb);
PurgeComm(hComm2,PURGE_TXCLEAR);
}
CMultiThreadComDlg dlg;
m_pMainWnd = &dlg;
int nResponse = dlg.DoModal();
if (nResponse == IDOK)
{
// TODO: Place code here to handle when the dialog is
// dismissed with OK
}
else if (nResponse == IDCANCEL)
{
// TODO: Place code here to handle when the dialog is
// dismissed with Cancel
}
return FALSE;
} |
此后我們在對話(huà)框CMultiThreadComDlg的初始化函數OnInitDialog中啟動(dòng)兩個(gè)分別處理COM1和COM2的線(xiàn)程：
BOOL CMultiThreadComDlg::OnInitDialog()
{
CDialog::OnInitDialog();
// Add "About..." menu item to system menu.
// IDM_ABOUTBOX must be in the system command range.
ASSERT((IDM_ABOUTBOX & 0xFFF0) == IDM_ABOUTBOX);
ASSERT(IDM_ABOUTBOX < 0xF000);
CMenu* pSysMenu = GetSystemMenu(FALSE);
if (pSysMenu != NULL)
{
CString strAboutMenu;
strAboutMenu.LoadString(IDS_ABOUTBOX);
if (!strAboutMenu.IsEmpty())
{
pSysMenu->AppendMenu(MF_SEPARATOR);
pSysMenu->AppendMenu(MF_STRING, IDM_ABOUTBOX, strAboutMenu);
}
}
// Set the icon for this dialog. The framework does this automatically
// when the application's main window is not a dialog
SetIcon(m_hIcon, TRUE); // Set big icon
SetIcon(m_hIcon, FALSE); // Set small icon
// TODO: Add extra initialization here
//啟動(dòng)串口1處理線(xiàn)程
DWORD nThreadId1;
hCommThread1 = ::CreateThread((LPSECURITY_ATTRIBUTES)NULL, 0,
(LPTHREAD_START_ROUTINE)Com1ThreadProcess, AfxGetMainWnd()->m_hWnd, 0, &nThreadId1);
if (hCommThread1 == NULL)
{
AfxMessageBox("創(chuàng )建串口1處理線(xiàn)程失敗");
return false;
}
//啟動(dòng)串口2處理線(xiàn)程
DWORD nThreadId2;
hCommThread2 = ::CreateThread((LPSECURITY_ATTRIBUTES)NULL, 0,
(LPTHREAD_START_ROUTINE)Com2ThreadProcess, AfxGetMainWnd()->m_hWnd, 0, &nThreadId2);
if (hCommThread2 == NULL)
{
AfxMessageBox("創(chuàng )建串口2處理線(xiàn)程失敗");
return false;
}
return TRUE; // return TRUE unless you set the focus to a control
} |
兩個(gè)串口COM1和COM2對應的線(xiàn)程處理函數等待串口上發(fā)生事件，并根據事件類(lèi)型和自身緩沖區是否有數據要發(fā)送進(jìn)行相應的處理，其源代碼為：
DWORD WINAPI Com1ThreadProcess(HWND hWnd//主窗口句柄)
{
DWORD wEven;
char str[10]; //讀入數據
SetCommMask(hComm1, EV_RXCHAR | EV_TXEMPTY);
while (TRUE)
{
WaitCommEvent(hComm1, &wEven, NULL);
if(wEven = 0)
{
CloseHandle(hCommThread1);
hCommThread1 = NULL;
ExitThread(0);
}
else
{
switch (wEven)
{
case EV_TXEMPTY:
if (wTxPos < wTxLen)
{
//在串口1寫(xiě)入數據
DWORD wCount; //寫(xiě)入的字節數
WriteFile(hComm1, com1Data.TxBuf[wTxPos], 1, &wCount, NULL);
com1Data.wTxPos++;
}
break;
case EV_RXCHAR:
if (com1Data.wRxPos < com1Data.wRxLen)
{
//讀取串口數據, 處理收到的數據
DWORD wCount; //讀取的字節數
ReadFile(hComm1, com1Data.RxBuf[wRxPos], 1, &wCount, NULL);
com1Data.wRxPos++;
if(com1Data.wRxPos== com1Data.wRxLen);
::PostMessage(hWnd, COM_SENDCHAR, 0, 1);
}
break;
}
}
}
}
return TRUE;
}
DWORD WINAPI Com2ThreadProcess(HWND hWnd //主窗口句柄)
{
DWORD wEven;
char str[10]; //讀入數據
SetCommMask(hComm2, EV_RXCHAR | EV_TXEMPTY);
while (TRUE)
{
WaitCommEvent(hComm2, &wEven, NULL);
if (wEven = 0)
{
CloseHandle(hCommThread2);
hCommThread2 = NULL;
ExitThread(0);
}
else
{
switch (wEven)
{
case EV_TXEMPTY:
if (wTxPos < wTxLen)
{
//在串口2寫(xiě)入數據
DWORD wCount; //寫(xiě)入的字節數
WriteFile(hComm2, com2Data.TxBuf[wTxPos], 1, &wCount, NULL);
com2Data.wTxPos++;
}
break;
case EV_RXCHAR:
if (com2Data.wRxPos < com2Data.wRxLen)
{
//讀取串口數據, 處理收到的數據
DWORD wCount; //讀取的字節數
ReadFile(hComm2, com2Data.RxBuf[wRxPos], 1, &wCount, NULL);
com2Data.wRxPos++;
if(com2Data.wRxPos== com2Data.wRxLen);
::PostMessage(hWnd, COM_SENDCHAR, 0, 1);
}
break;
}
}
}
return TRUE;
} |
線(xiàn)程控制函數中所操作的com1Data和com2Data是與串口對應的數據結構struct tagSerialPort的實(shí)例，這個(gè)數據結構是：
typedef struct tagSerialPort
{
BYTE RxBuf[SPRX_BUFLEN];//接收Buffer
WORD wRxPos; //當前接收字節位置
WORD wRxLen; //要接收的字節數
BYTE TxBuf[SPTX_BUFLEN];//發(fā)送Buffer
WORD wTxPos; //當前發(fā)送字節位置
WORD wTxLen; //要發(fā)送的字節數
}SerialPort, * LPSerialPort; |
3.多線(xiàn)程串口類(lèi)
使用多線(xiàn)程串口通信更方便的途徑是編寫(xiě)一個(gè)多線(xiàn)程的串口類(lèi)，例如Remon Spekreijse編寫(xiě)了一個(gè)CSerialPort串口類(lèi)。仔細分析這個(gè)類(lèi)的源代碼，將十分有助于我們對先前所學(xué)多線(xiàn)程及同步知識的理解。
3.1類(lèi)的定義
#ifndef __SERIALPORT_H__
#define __SERIALPORT_H__
#define WM_COMM_BREAK_DETECTED WM_USER+1 // A break was detected on input.
#define WM_COMM_CTS_DETECTED WM_USER+2 // The CTS (clear-to-send) signal changed state.
#define WM_COMM_DSR_DETECTED WM_USER+3 // The DSR (data-set-ready) signal changed state.
#define WM_COMM_ERR_DETECTED WM_USER+4 // A line-status error occurred. Line-status errors are CE_FRAME, CE_OVERRUN, and CE_RXPARITY.
#define WM_COMM_RING_DETECTED WM_USER+5 // A ring indicator was detected.
#define WM_COMM_RLSD_DETECTED WM_USER+6 // The RLSD (receive-line-signal-detect) signal changed state.
#define WM_COMM_RXCHAR WM_USER+7 // A character was received and placed in the input buffer.
#define WM_COMM_RXFLAG_DETECTED WM_USER+8 // The event character was received and placed in the input buffer.
#define WM_COMM_TXEMPTY_DETECTED WM_USER+9 // The last character in the output buffer was sent.
class CSerialPort
{
public:
// contruction and destruction
CSerialPort();
virtual ~CSerialPort();
// port initialisation
BOOL InitPort(CWnd* pPortOwner, UINT portnr = 1, UINT baud = 19200, char parity = 'N', UINT databits = 8, UINT stopsbits = 1, DWORD dwCommEvents = EV_RXCHAR | EV_CTS, UINT nBufferSize = 512);
// start/stop comm watching
BOOL StartMonitoring();
BOOL RestartMonitoring();
BOOL StopMonitoring();
DWORD GetWriteBufferSize();
DWORD GetCommEvents();
DCB GetDCB();
void WriteToPort(char* string);
protected:
// protected memberfunctions
void ProcessErrorMessage(char* ErrorText);
static UINT CommThread(LPVOID pParam);
static void ReceiveChar(CSerialPort* port, COMSTAT comstat);
static void WriteChar(CSerialPort* port);
// thread
CWinThread* m_Thread;
// synchronisation objects
CRITICAL_SECTION m_csCommunicationSync;
BOOL m_bThreadAlive;
// handles
HANDLE m_hShutdownEvent;
HANDLE m_hComm;
HANDLE m_hWriteEvent;
// Event array.
// One element is used for each event. There are two event handles for each port.
// A Write event and a receive character event which is located in the overlapped structure (m_ov.hEvent).
// There is a general shutdown when the port is closed.
HANDLE m_hEventArray[3];
// structures
OVERLAPPED m_ov;
COMMTIMEOUTS m_CommTimeouts;
DCB m_dcb;
// owner window
CWnd* m_pOwner;
// misc
UINT m_nPortNr;
char* m_szWriteBuffer;
DWORD m_dwCommEvents;
DWORD m_nWriteBufferSize;
};
#endif __SERIALPORT_H__ |
3.2類(lèi)的實(shí)現
3.2.1構造函數與析構函數
進(jìn)行相關(guān)變量的賦初值及內存恢復：
CSerialPort::CSerialPort()
{
m_hComm = NULL;
// initialize overlapped structure members to zero
m_ov.Offset = 0;
m_ov.OffsetHigh = 0;
// create events
m_ov.hEvent = NULL;
m_hWriteEvent = NULL;
m_hShutdownEvent = NULL;
m_szWriteBuffer = NULL;
m_bThreadAlive = FALSE;
}
//
// Delete dynamic memory
//
CSerialPort::~CSerialPort()
{
do
{
SetEvent(m_hShutdownEvent);
}
while (m_bThreadAlive);
TRACE("Thread ended\n");
delete []m_szWriteBuffer;
} |
3.2.2核心函數：初始化串口
在初始化串口函數中，將打開(kāi)串口，設置相關(guān)參數，并創(chuàng )建串口相關(guān)的用戶(hù)控制事件，初始化臨界區（Critical Section），以成隊的EnterCriticalSection()、LeaveCriticalSection()函數進(jìn)行資源的排它性訪(fǎng)問(wèn)：
BOOL CSerialPort::InitPort(CWnd *pPortOwner,
// the owner (CWnd) of the port (receives message)
UINT portnr, // portnumber (1..4)
UINT baud, // baudrate
char parity, // parity
UINT databits, // databits
UINT stopbits, // stopbits
DWORD dwCommEvents, // EV_RXCHAR, EV_CTS etc
UINT writebuffersize) // size to the writebuffer
{
assert(portnr > 0 && portnr < 5);
assert(pPortOwner != NULL);
// if the thread is alive: Kill
if (m_bThreadAlive)
{
do
{
SetEvent(m_hShutdownEvent);
}
while (m_bThreadAlive);
TRACE("Thread ended\n");
}
// create events
if (m_ov.hEvent != NULL)
ResetEvent(m_ov.hEvent);
m_ov.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
if (m_hWriteEvent != NULL)
ResetEvent(m_hWriteEvent);
m_hWriteEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
if (m_hShutdownEvent != NULL)
ResetEvent(m_hShutdownEvent);
m_hShutdownEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
// initialize the event objects
m_hEventArray[0] = m_hShutdownEvent; // highest priority
m_hEventArray[1] = m_ov.hEvent;
m_hEventArray[2] = m_hWriteEvent;
// initialize critical section
InitializeCriticalSection(&m_csCommunicationSync);
// set buffersize for writing and save the owner
m_pOwner = pPortOwner;
if (m_szWriteBuffer != NULL)
delete []m_szWriteBuffer;
m_szWriteBuffer = new char[writebuffersize];
m_nPortNr = portnr;
m_nWriteBufferSize = writebuffersize;
m_dwCommEvents = dwCommEvents;
BOOL bResult = FALSE;
char *szPort = new char[50];
char *szBaud = new char[50];
// now it critical!
EnterCriticalSection(&m_csCommunicationSync);
// if the port is already opened: close it
if (m_hComm != NULL)
{
CloseHandle(m_hComm);
m_hComm = NULL;
}
// prepare port strings
sprintf(szPort, "COM%d", portnr);
sprintf(szBaud, "baud=%d parity=%c data=%d stop=%d", baud, parity, databits,stopbits);
// get a handle to the port
m_hComm = CreateFile(szPort, // communication port string (COMX)
GENERIC_READ | GENERIC_WRITE, // read/write types
0, // comm devices must be opened with exclusive access
NULL, // no security attributes
OPEN_EXISTING, // comm devices must use OPEN_EXISTING
FILE_FLAG_OVERLAPPED, // Async I/O
0); // template must be 0 for comm devices
if (m_hComm == INVALID_HANDLE_VALUE)
{
// port not found
delete []szPort;
delete []szBaud;
return FALSE;
}
// set the timeout values
m_CommTimeouts.ReadIntervalTimeout = 1000;
m_CommTimeouts.ReadTotalTimeoutMultiplier = 1000;
m_CommTimeouts.ReadTotalTimeoutConstant = 1000;
m_CommTimeouts.WriteTotalTimeoutMultiplier = 1000;
m_CommTimeouts.WriteTotalTimeoutConstant = 1000;
// configure
if (SetCommTimeouts(m_hComm, &m_CommTimeouts))
{
if (SetCommMask(m_hComm, dwCommEvents))
{
if (GetCommState(m_hComm, &m_dcb))
{
m_dcb.fRtsControl = RTS_CONTROL_ENABLE; // set RTS bit high!
if (BuildCommDCB(szBaud, &m_dcb))
{
if (SetCommState(m_hComm, &m_dcb))
;
// normal operation... continue
else
ProcessErrorMessage("SetCommState()");
}
else
ProcessErrorMessage("BuildCommDCB()");
}
else
ProcessErrorMessage("GetCommState()");
}
else
ProcessErrorMessage("SetCommMask()");
}
else
ProcessErrorMessage("SetCommTimeouts()");
delete []szPort;
delete []szBaud;
// flush the port
PurgeComm(m_hComm, PURGE_RXCLEAR | PURGE_TXCLEAR | PURGE_RXABORT | PURGE_TXABORT);
// release critical section
LeaveCriticalSection(&m_csCommunicationSync);
TRACE("Initialisation for communicationport %d completed.\nUse Startmonitor to communicate.\n", portnr);
return TRUE;
} |
3.3.3核心函數：串口線(xiàn)程控制函數
串口線(xiàn)程處理函數是整個(gè)類(lèi)中最核心的部分，它主要完成兩類(lèi)工作：
?。?）利用WaitCommEvent函數對串口上發(fā)生的事件進(jìn)行獲取并根據事件的不同類(lèi)型進(jìn)行相應的處理；
?。?）利用WaitForMultipleObjects函數對串口相關(guān)的用戶(hù)控制事件進(jìn)行等待并做相應處理。
UINT CSerialPort::CommThread(LPVOID pParam)
{
// Cast the void pointer passed to the thread back to
// a pointer of CSerialPort class
CSerialPort *port = (CSerialPort*)pParam;
// Set the status variable in the dialog class to
// TRUE to indicate the thread is running.
port->m_bThreadAlive = TRUE;
// Misc. variables
DWORD BytesTransfered = 0;
DWORD Event = 0;
DWORD CommEvent = 0;
DWORD dwError = 0;
COMSTAT comstat;
BOOL bResult = TRUE;
// Clear comm buffers at startup
if (port->m_hComm)
// check if the port is opened
PurgeComm(port->m_hComm, PURGE_RXCLEAR | PURGE_TXCLEAR | PURGE_RXABORT | PURGE_TXABORT);
// begin forever loop. This loop will run as long as the thread is alive.
for (;;)
{
// Make a call to WaitCommEvent(). This call will return immediatly
// because our port was created as an async port (FILE_FLAG_OVERLAPPED
// and an m_OverlappedStructerlapped structure specified). This call will cause the
// m_OverlappedStructerlapped element m_OverlappedStruct.hEvent, which is part of the m_hEventArray to
// be placed in a non-signeled state if there are no bytes available to be read,
// or to a signeled state if there are bytes available. If this event handle
// is set to the non-signeled state, it will be set to signeled when a
// character arrives at the port.
// we do this for each port!
bResult = WaitCommEvent(port->m_hComm, &Event, &port->m_ov);
if (!bResult)
{
// If WaitCommEvent() returns FALSE, process the last error to determin
// the reason..
switch (dwError = GetLastError())
{
case ERROR_IO_PENDING:
{
// This is a normal return value if there are no bytes
// to read at the port.
// Do nothing and continue
break;
}
case 87:
{
// Under Windows NT, this value is returned for some reason.
// I have not investigated why, but it is also a valid reply
// Also do nothing and continue.
break;
}
default:
{
// All other error codes indicate a serious error has
// occured. Process this error.
port->ProcessErrorMessage("WaitCommEvent()");
break;
}
}
}
else
{
// If WaitCommEvent() returns TRUE, check to be sure there are
// actually bytes in the buffer to read.
//
// If you are reading more than one byte at a time from the buffer
// (which this program does not do) you will have the situation occur
// where the first byte to arrive will cause the WaitForMultipleObjects()
// function to stop waiting. The WaitForMultipleObjects() function
// resets the event handle in m_OverlappedStruct.hEvent to the non-signelead state
// as it returns.
//
// If in the time between the reset of this event and the call to
// ReadFile() more bytes arrive, the m_OverlappedStruct.hEvent handle will be set again
// to the signeled state. When the call to ReadFile() occurs, it will
// read all of the bytes from the buffer, and the program will
// loop back around to WaitCommEvent().
//
// At this point you will be in the situation where m_OverlappedStruct.hEvent is set,
// but there are no bytes available to read. If you proceed and call
// ReadFile(), it will return immediatly due to the async port setup, but
// GetOverlappedResults() will not return until the next character arrives.
//
// It is not desirable for the GetOverlappedResults() function to be in
// this state. The thread shutdown event (event 0) and the WriteFile()
// event (Event2) will not work if the thread is blocked by GetOverlappedResults().
//
// The solution to this is to check the buffer with a call to ClearCommError().
// This call will reset the event handle, and if there are no bytes to read
// we can loop back through WaitCommEvent() again, then proceed.
// If there are really bytes to read, do nothing and proceed.
bResult = ClearCommError(port->m_hComm, &dwError, &comstat);
if (comstat.cbInQue == 0)
continue;
} // end if bResult
// Main wait function. This function will normally block the thread
// until one of nine events occur that require action.
Event = WaitForMultipleObjects(3, port->m_hEventArray, FALSE, INFINITE);
switch (Event)
{
case 0:
{
// Shutdown event. This is event zero so it will be
// the higest priority and be serviced first.
port->m_bThreadAlive = FALSE;
// Kill this thread. break is not needed, but makes me feel better.
AfxEndThread(100);
break;
}
case 1:
// read event
{
GetCommMask(port->m_hComm, &CommEvent);
if (CommEvent &EV_CTS)
::SendMessage(port->m_pOwner->m_hWnd, WM_COMM_CTS_DETECTED, (WPARAM)0, (LPARAM)port->m_nPortNr);
if (CommEvent &EV_RXFLAG)
::SendMessage(port->m_pOwner->m_hWnd, WM_COMM_RXFLAG_DETECTED,(WPARAM)0, (LPARAM)port->m_nPortNr);
if (CommEvent &EV_BREAK)
::SendMessage(port->m_pOwner->m_hWnd, WM_COMM_BREAK_DETECTED,(WPARAM)0, (LPARAM)port->m_nPortNr);
if (CommEvent &EV_ERR)
::SendMessage(port->m_pOwner->m_hWnd, WM_COMM_ERR_DETECTED, (WPARAM)0, (LPARAM)port->m_nPortNr);
if (CommEvent &EV_RING)
::SendMessage(port->m_pOwner->m_hWnd, WM_COMM_RING_DETECTED,(WPARAM)0, (LPARAM)port->m_nPortNr);
if (CommEvent &EV_RXCHAR)
// Receive character event from port.
ReceiveChar(port, comstat);
break;
}
case 2:
// write event
{
// Write character event from port
WriteChar(port);
break;
}
} // end switch
} // close forever loop
return 0;
} |
下列三個(gè)函數用于對串口線(xiàn)程進(jìn)行啟動(dòng)、掛起和恢復：
//
// start comm watching
//
BOOL CSerialPort::StartMonitoring()
{
if (!(m_Thread = AfxBeginThread(CommThread, this)))
return FALSE;
TRACE("Thread started\n");
return TRUE;
}
//
// Restart the comm thread
//
BOOL CSerialPort::RestartMonitoring()
{
TRACE("Thread resumed\n");
m_Thread->ResumeThread();
return TRUE;
}
//
// Suspend the comm thread
//
BOOL CSerialPort::StopMonitoring()
{
TRACE("Thread suspended\n");
m_Thread->SuspendThread();
return TRUE;
} |
3.3.4讀寫(xiě)串口
下面一組函數是用戶(hù)對串口進(jìn)行讀寫(xiě)操作的接口：
//
// Write a character.
//
void CSerialPort::WriteChar(CSerialPort *port)
{
BOOL bWrite = TRUE;
BOOL bResult = TRUE;
DWORD BytesSent = 0;
ResetEvent(port->m_hWriteEvent);
// Gain ownership of the critical section
EnterCriticalSection(&port->m_csCommunicationSync);
if (bWrite)
{
// Initailize variables
port->m_ov.Offset = 0;
port->m_ov.OffsetHigh = 0;
// Clear buffer
PurgeComm(port->m_hComm, PURGE_RXCLEAR | PURGE_TXCLEAR | PURGE_RXABORT | PURGE_TXABORT);
bResult = WriteFile(port->m_hComm, // Handle to COMM Port
port->m_szWriteBuffer, // Pointer to message buffer in calling finction
strlen((char*)port->m_szWriteBuffer), // Length of message to send
&BytesSent, // Where to store the number of bytes sent
&port->m_ov); // Overlapped structure
// deal with any error codes
if (!bResult)
{
DWORD dwError = GetLastError();
switch (dwError)
{
case ERROR_IO_PENDING:
{
// continue to GetOverlappedResults()
BytesSent = 0;
bWrite = FALSE;
break;
}
default:
{
// all other error codes
port->ProcessErrorMessage("WriteFile()");
}
}
}
else
{
LeaveCriticalSection(&port->m_csCommunicationSync);
}
} // end if(bWrite)
if (!bWrite)
{
bWrite = TRUE;
bResult = GetOverlappedResult(port->m_hComm, // Handle to COMM port
&port->m_ov, // Overlapped structure
&BytesSent, // Stores number of bytes sent
TRUE); // Wait flag
LeaveCriticalSection(&port->m_csCommunicationSync);
// deal with the error code
if (!bResult)
{
port->ProcessErrorMessage("GetOverlappedResults() in WriteFile()");
}
} // end if (!bWrite)
// Verify that the data size send equals what we tried to send
if (BytesSent != strlen((char*)port->m_szWriteBuffer))
{
TRACE("WARNING: WriteFile() error.. Bytes Sent: %d; Message Length: %d\n",
BytesSent, strlen((char*)port->m_szWriteBuffer));
}
}
//
// Character received. Inform the owner
//
void CSerialPort::ReceiveChar(CSerialPort *port, COMSTAT comstat)
{
BOOL bRead = TRUE;
BOOL bResult = TRUE;
DWORD dwError = 0;
DWORD BytesRead = 0;
unsigned char RXBuff;
for (;;)
{
// Gain ownership of the comm port critical section.
// This process guarantees no other part of this program
// is using the port object.
EnterCriticalSection(&port->m_csCommunicationSync);
// ClearCommError() will update the COMSTAT structure and
// clear any other errors.
bResult = ClearCommError(port->m_hComm, &dwError, &comstat);
LeaveCriticalSection(&port->m_csCommunicationSync);
// start forever loop. I use this type of loop because I
// do not know at runtime how many loops this will have to
// run. My solution is to start a forever loop and to
// break out of it when I have processed all of the
// data available. Be careful with this approach and
// be sure your loop will exit.
// My reasons for this are not as clear in this sample
// as it is in my production code, but I have found this
// solutiion to be the most efficient way to do this.
if (comstat.cbInQue == 0)
{
// break out when all bytes have been read
break;
}
EnterCriticalSection(&port->m_csCommunicationSync);
if (bRead)
{
bResult = ReadFile(port->m_hComm, // Handle to COMM port
&RXBuff, // RX Buffer Pointer
1, // Read one byte
&BytesRead, // Stores number of bytes read
&port->m_ov); // pointer to the m_ov structure
// deal with the error code
if (!bResult)
{
switch (dwError = GetLastError())
{
case ERROR_IO_PENDING:
{
// asynchronous i/o is still in progress
// Proceed on to GetOverlappedResults();
bRead = FALSE;
break;
}
default:
{
// Another error has occured. Process this error.
port->ProcessErrorMessage("ReadFile()");
break;
}
}
}
else
{
// ReadFile() returned complete. It is not necessary to call GetOverlappedResults()
bRead = TRUE;
}
} // close if (bRead)
if (!bRead)
{
bRead = TRUE;
bResult = GetOverlappedResult(port->m_hComm, // Handle to COMM port
&port->m_ov, // Overlapped structure
&BytesRead, // Stores number of bytes read
TRUE); // Wait flag
// deal with the error code
if (!bResult)
{
port->ProcessErrorMessage("GetOverlappedResults() in ReadFile()");
}
} // close if (!bRead)
LeaveCriticalSection(&port->m_csCommunicationSync);
// notify parent that a byte was received
::SendMessage((port->m_pOwner)->m_hWnd, WM_COMM_RXCHAR, (WPARAM)RXBuff,(LPARAM)port->m_nPortNr);
} // end forever loop
}
//
// Write a string to the port
//
void CSerialPort::WriteToPort(char *string)
{
assert(m_hComm != 0);
memset(m_szWriteBuffer, 0, sizeof(m_szWriteBuffer));
strcpy(m_szWriteBuffer, string);
// set event for write
SetEvent(m_hWriteEvent);
}
//
// Return the output buffer size
//
DWORD CSerialPort::GetWriteBufferSize()
{
return m_nWriteBufferSize;
} |
3.3.5控制接口
應用程序員使用下列一組public函數可以獲取串口的DCB及串口上發(fā)生的事件：
//
// Return the device control block
//
DCB CSerialPort::GetDCB()
{
return m_dcb;
}
//
// Return the communication event masks
//
DWORD CSerialPort::GetCommEvents()
{
return m_dwCommEvents;
} |
3.3.6錯誤處理
//
// If there is a error, give the right message
//
void CSerialPort::ProcessErrorMessage(char *ErrorText)
{
char *Temp = new char[200];
LPVOID lpMsgBuf;
FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM,
NULL, GetLastError(), MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
// Default language
(LPTSTR) &lpMsgBuf, 0, NULL);
sprintf(Temp,
"WARNING: %s Failed with the following error: \n%s\nPort: %d\n", (char*)
ErrorText, lpMsgBuf, m_nPortNr);
MessageBox(NULL, Temp, "Application Error", MB_ICONSTOP);
LocalFree(lpMsgBuf);
delete []Temp;
} |
仔細分析Remon Spekreijse的CSerialPort類(lèi)對我們理解多線(xiàn)程及其同步機制是大有益處的，從http://codeguru.earthweb.com/network/serialport.shtml我們可以獲取CSerialPort類(lèi)的介紹與工程實(shí)例。另外，電子工業(yè)出版社《Visual C++/Turbo C串口通信編程實(shí)踐》一書(shū)的作者龔建偉也編寫(xiě)了一個(gè)使用CSerialPort類(lèi)的例子，可以從http://www.gjwtech.com/scomm/sc2serialportclass.htm獲得詳情。
4.多線(xiàn)程網(wǎng)絡(luò )通信
在網(wǎng)絡(luò )通信中使用多線(xiàn)程主要有兩種途徑，即主監控線(xiàn)程和線(xiàn)程池。
4.1主監控線(xiàn)程
這種方式指的是程序中使用一個(gè)主線(xiàn)程監控某特定端口，一旦在這個(gè)端口上發(fā)生連接請求，則主監控線(xiàn)程動(dòng)態(tài)使用CreateThread派生出新的子線(xiàn)程處理該請求。主線(xiàn)程在派生子線(xiàn)程后不再對子線(xiàn)程加以控制和調度，而由子線(xiàn)程獨自和客戶(hù)方發(fā)生連接并處理異常。
使用這種方法的優(yōu)點(diǎn)是：
?。?）可以較快地實(shí)現原型設計，尤其在用戶(hù)數目較少、連接保持時(shí)間較長(cháng)時(shí)有表現較好；
?。?）主線(xiàn)程不與子線(xiàn)程發(fā)生通信，在一定程度上減少了系統資源的消耗。
其缺點(diǎn)是：
?。?）生成和終止子線(xiàn)程的開(kāi)銷(xiāo)比較大；
?。?）對遠端用戶(hù)的控制較弱。
這種多線(xiàn)程方式總的特點(diǎn)是"動(dòng)態(tài)生成，靜態(tài)調度"。
4.2線(xiàn)程池
這種方式指的是主線(xiàn)程在初始化時(shí)靜態(tài)地生成一定數量的懸掛子線(xiàn)程，放置于線(xiàn)程池中。隨后，主線(xiàn)程將對這些懸掛子線(xiàn)程進(jìn)行動(dòng)態(tài)調度。一旦客戶(hù)發(fā)出連接請求，主線(xiàn)程將從線(xiàn)程池中查找一個(gè)懸掛的子線(xiàn)程：
?。?）如果找到，主線(xiàn)程將該連接分配給這個(gè)被發(fā)現的子線(xiàn)程。子線(xiàn)程從主線(xiàn)程處接管該連接，并與用戶(hù)通信。當連接結束時(shí)，該子線(xiàn)程將自動(dòng)懸掛，并進(jìn)人線(xiàn)程池等待再次被調度；
?。?）如果當前已沒(méi)有可用的子線(xiàn)程，主線(xiàn)程將通告發(fā)起連接的客戶(hù)。
使用這種方法進(jìn)行設計的優(yōu)點(diǎn)是：
?。?）主線(xiàn)程可以更好地對派生的子線(xiàn)程進(jìn)行控制和調度；
?。?）對遠程用戶(hù)的監控和管理能力較強。
雖然主線(xiàn)程對子線(xiàn)程的調度要消耗一定的資源，但是與主監控線(xiàn)程方式中派生和終止線(xiàn)程所要耗費的資源相比，要少很多。因此，使用該種方法設計和實(shí)現的系統在客戶(hù)端連接和終止變更頻繁時(shí)有上佳表現。
這種多線(xiàn)程方式總的特點(diǎn)是"靜態(tài)生成，動(dòng)態(tài)調度"。
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