C / C++ / MFC

// CMyApplicationApp.cpp
...
CSemaphore csLock(1,1,"MYSTRING",NULL);
...
BOOL CMyApplication::InitInstance()
{
 ...
 if(csLock.Lock(100))
 {
   AfxMessageBox("One Instance is already running");
   return false;
 }
 ...
}
...
int CMyApplication::ExitInstance()
{
  csLock.Unlock();
  ...
}

BOOL MyApp::InitInstance()<br />
{<br />
<br />
if( !m_Instance.Init()) // m_instance is a member of app class<br />
        return 0;<br />
....<br />
}

ashishbhatt wrote:

m_mutex = CreateMutex(NULL,FALSE,LPCWSTR(mutexname));

<br />
class RTMPInstanceHandler<br />
{<br />
    HANDLE m_mutex;<br />
public:<br />
    RTMPInstanceHandler():m_mutex(NULL)<br />
    {<br />
    }<br />
<br />
    ~RTMPInstanceHandler()<br />
    {<br />
        // make sure mutex is cleared as we exit<br />
        Release();<br />
    }<br />
<br />
    BOOL Init()<br />
    {<br />
        // Create the named mutex<br />
        m_mutex = CreateMutex(NULL,FALSE,_T("mutexname"));<br />
        if(m_mutex == NULL)<br />
        {<br />
            return FALSE;<br />
        }<br />
<br />
        // Check that the mutex didn't already exist<br />
        if (GetLastError() == ERROR_ALREADY_EXISTS)<br />
        {<br />
            return FALSE;<br />
        }<br />
        return TRUE;<br />
    }<br />
<br />
    //<br />
    // allow mutex to be explicitely cleared<br />
    //<br />
    DWORD Release()<br />
    {<br />
        try<br />
        {<br />
            CloseHandle(m_mutex);<br />
        }<br />
        catch (...)<br />
        {<br />
            //<br />
            // Release() should be called once from the user code,<br />
            // and a second time by the object's destructor.<br />
            // the second call will cause an exception.<br />
            // we can just ignore it.<br />
            //<br />
        }<br />
<br />
        return GetLastError();<br />
    }<br />
};<br />
<br />
int _tmain(int argc, TCHAR* argv[], TCHAR* envp[])<br />
{<br />
    int nRetCode = 0;<br />
<br />
<br />
    RTMPInstanceHandler inst;<br />
    if ( !inst.Init())<br />
    {<br />
        cout<<"instance already exists";<br />
        return nRetCode;<br />
    }<br />
<br />
    cin >> nRetCode;<br />
    return nRetCode;<br />
}<br />

BOOL CMyApp::InitInstance()
{
	m_hMutex = ::CreateMutex(0, FALSE, "TestApp");
	if (::GetLastError() == ERROR_ALREADY_EXISTS) {
		TRACE("TestApp: Already running");
		// explicitly close the mutex handle
		::CloseHandle(m_hMutex);
		
		return FALSE;	// do not run second time
	}
}

BOOL CMfctestApp::InitInstance()
{
	//...

	m_hMutex = ::CreateMutex(0, FALSE, "TestApp");
	if (::GetLastError() == ERROR_ALREADY_EXISTS)
	{
		TRACE("TestApp: Already running");
		// explicitly close the mutex handle
		::CloseHandle(m_hMutex), m_hMutex = 0;
		return FALSE;	// do not run second time
	}
	
	// ...
}

class CMfctestApp : public CWinApp
{
	// ...
private:
	HANDLE m_hMutex;
};

int CMfctestApp::ExitInstance() 
{
	if (m_hMutex)
		::CloseHandle(m_hMutex);
	
	return CWinApp::ExitInstance();
}

ExitInstance()
{
	if(m_hMutex)
	{
		::CloseHandle(m_hMutex);
                ReleaseMutex(m_hMutex);
	}
       //here suppose the program will not run to following code.
       //but it did now.ReleaseMutex should release the m_hMutex already right?
	if(m_hMutex)
	{
		::CloseHandle(m_hMutex);
                ReleaseMutex(m_hMutex);
	}
		
	return CWinApp::ExitInstance();