Obtaining Directory Change Notifications

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转载最新推荐文章于 2020-12-25 19:42:05 发布 · 147 阅读

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原文链接：http://www.cnblogs.com/pangpangxiong/archive/2009/09/08/1562630.html

本文介绍使用Win32 API实现文件和目录变更通知的方法，包括使用FindFirstChangeNotification、FindNextChangeNotification和ReadDirectoryChangesW函数监测指定目录及其子目录的变更。通过创建线程并等待变更通知，然后比较新旧目录状态来获取具体变更。

Obtaining Directory Change Notifications

About APIs, you can go to this link: http://msdn.microsoft.com/en-us/library/aa365261(VS.85).aspx

Note following items extracted from MSDN:

1. The wait functions can monitor the specified directory or subtree by using the handle returned by the FindFirstChangeNotification function. A wait is satisfied when one of the filter conditions occurs in the monitored directory or subtree.

2. After the wait has been satisfied, the application can respond to this condition and continue monitoring the directory by calling the FindNextChangeNotification function and the appropriate wait function. When the handle is no longer needed, it can be closed by using the FindCloseChangeNotification function.

3. This function does not indicate the change that satisfied the wait condition. To retrieve information about the specific change as part of the notification, use the ReadDirectoryChangesW function.

To read the changes, we can use a WIN32_FIND_DATA list to keep the old attributes of the directory.

1. Adding the specified folder to monitor queue

void CFileMonitor::Add(const _bstr_t &file)

{

CFileMonitor *pThis = new CFileMonitor(file);

//Reading files in the directory

pThis->RefreshDirectory(FALSE);

pThis->SetChange(::FindFirstChangeNotification(

path,

FALSE,

FILE_NOTIFY_CHANGE_FILE_NAME | FILE_NOTIFY_CHANGE_LAST_WRITE

));

if (pThis->GetChange() == INVALID_HANDLE_VALUE)

{

delete pThis;

return;

}

DWORD ThreadId;

HANDLE ht = ::CreateThread(

NULL,

0, CFileMonitor::ThreadAdd,

pThis,

&ThreadId);

if (ht == NULL)

delete pThis;

else

::CloseHandle(ht);

}

2. In thread Add, wait and capture the change notification

DWORD WINAPI CFileMonitor::ThreadAdd(LPVOID lpParameter)

{

CFileMonitor *pThis = (CFileMonitor *)lpParameter;

DWORD rc;

{

//TODO: I should have a timeout value

rc = ::WaitForSingleObject(pThis->GetChange(), INFINITE);

// take new snap shot of directory and get notification of changes

pThis->RefreshDirectory();

} while(!pThis->IsAdded() && rc == WAIT_OBJECT_0);

// cleanup

delete pThis;

return 0;

}

3. Compare the items

void CFileMonitor::RefreshDirectory(BOOL bNotify /* default is TRUE */)

{

if (m_path.length() == 0)

return;

// find all the files that match the path spec

int count = 0;

WIN32_FIND_DATA *pFindArray = NULL;

WIN32_FIND_DATA FindFileData;

HANDLE hFind = ::FindFirstFile(m_path, &FindFileData);

BOOL more = hFind != INVALID_HANDLE_VALUE;

while(more)

{

if ((FindFileData.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) == 0) // skip directories

{

// allocate a new entry in this snap shot (pFinDArray)

count++;

pFindArray = (WIN32_FIND_DATA *)realloc(pFindArray, count * sizeof(*pFindArray));

// add this file to the new snap shot

memcpy(pFindArray + count - 1, &FindFileData, sizeof(*pFindArray));

if (bNotify)

{

DWORD fcs = GetFileStatus(m_pFindArray, m_count, FindFileData);

if (fcs != FILE_CHANGE_NONE)

OnFileChange(FindFileData, fcs);

}

more = ::FindNextFile(hFind, &FindFileData);

}

if (m_pFindArray)

free(m_pFindArray);

m_pFindArray = pFindArray;

m_count = count;

}

转载于:https://www.cnblogs.com/pangpangxiong/archive/2009/09/08/1562630.html