sinstance.cpp

这个则是一个简单的监视文件系统的例子

/*
Module : SINSTANCE.CPP
Purpose: Defines the implementation for an MFC wrapper classe
         to do instance checking
Created: PJN / 29-07-1998
History: None

Copyright (c) 1998 by PJ Naughter.  
All rights reserved.

*/


/////////////////////////////////  Includes  //////////////////////////////////
#include "stdafx.h"
#include "sinstance.h"



#ifdef _DEBUG
#undef THIS_FILE
static char BASED_CODE THIS_FILE[] = __FILE__;
#define new DEBUG_NEW
#endif



///////////////////////////////// Implementation //////////////////////////////

//struct which is put into shared memory
struct CWindowInstance
{
  HWND hMainWnd;
};

//Class which be used as a static to ensure that we
//only close the file mapping at the very last chance
class _INSTANCE_DATA
{
public:
	_INSTANCE_DATA();
  ~_INSTANCE_DATA();

protected:
	HANDLE hInstanceData;
	friend class CInstanceChecker;
};

_INSTANCE_DATA::_INSTANCE_DATA()
{
	hInstanceData = NULL;
}

_INSTANCE_DATA::~_INSTANCE_DATA()
{
  if (hInstanceData != NULL)
	{
    ::CloseHandle(hInstanceData);
    hInstanceData = NULL;
	}
}

static _INSTANCE_DATA instanceData;

CInstanceChecker::CInstanceChecker()
{
	// Only one object of type CInstanceChecker should be created
	VERIFY(instanceData.hInstanceData == NULL);

	m_hPrevInstance = NULL;
}

BOOL CInstanceChecker::PreviousInstanceRunning()
{
  //MMF name is taken from MFC's AfxGetAppName
  LPCTSTR pszAppName = AfxGetAppName(); 
  ASSERT(pszAppName);
  ASSERT(_tcslen(pszAppName)); //Missing the Application Title ?
  CString sMMF(_T("CInstanceChecker_MMF_"));
	sMMF += pszAppName;

  //Try to open the MMF first to see if we are the second instance
	m_hPrevInstance = ::OpenFileMapping( FILE_MAP_ALL_ACCESS, FALSE, sMMF);

  //If this is the first instance then copy in our info into the shared memory
  if (m_hPrevInstance == NULL)
  {
		//Create the MMF
		int nMMFSize = sizeof(CWindowInstance);
		instanceData.hInstanceData = ::CreateFileMapping((HANDLE)0xFFFFFFFF, NULL, PAGE_READWRITE, 0, nMMFSize, sMMF);
    VERIFY(instanceData.hInstanceData != NULL); //Creating the MMF should work

    //Open the MMF
   	CWindowInstance* pInstanceData = (CWindowInstance*) ::MapViewOfFile(instanceData.hInstanceData, FILE_MAP_READ | FILE_MAP_WRITE, 0, 0, nMMFSize);
    VERIFY(pInstanceData != NULL);   //Opening the MMF should work

   	// Lock the data prior to updating it
	  CSingleLock dataLock(&m_instanceDataMutex, TRUE);

    ASSERT(AfxGetMainWnd() != NULL); //Did you forget to set up the mainfrm in InitInstance ?
    ASSERT(AfxGetMainWnd()->GetSafeHwnd() != NULL);
    pInstanceData->hMainWnd = AfxGetMainWnd()->GetSafeHwnd();

		VERIFY(::UnmapViewOfFile(pInstanceData));
  }

  return (m_hPrevInstance != NULL); 
}

void CInstanceChecker::ActivatePreviousInstance()
{
  VERIFY(m_hPrevInstance != NULL); //Whats happened to my handle !
  
  //Open up the MMF
	int nMMFSize = sizeof(CWindowInstance);
  CWindowInstance* pInstanceData = (CWindowInstance*) ::MapViewOfFile(m_hPrevInstance, FILE_MAP_READ | FILE_MAP_WRITE, 0, 0, nMMFSize);
  VERIFY(pInstanceData != NULL); //Opening the MMF should work

  // Lock the data prior to reading from it
	CSingleLock dataLock(&m_instanceDataMutex, TRUE);

  //activate the old window
  HWND hWindow = pInstanceData->hMainWnd;
  CWnd wndPrev; 
	wndPrev.Attach(hWindow);
	CWnd* pWndChild = wndPrev.GetLastActivePopup();

	if (wndPrev.IsIconic())
		wndPrev.ShowWindow(SW_RESTORE); 

	pWndChild->SetForegroundWindow();

	//Detach the CWnd we were using
	wndPrev.Detach();

  //Unmap the MMF we were using
	VERIFY(::UnmapViewOfFile(pInstanceData));

	//Close the MMF
	VERIFY(::CloseHandle(m_hPrevInstance));
	m_hPrevInstance = NULL;
}