c++ - 使用 Windows C++ LockFIle() 锁定文件然后从中获取流？

Question

我已经使用 LockFileEx 锁定了一个文件，但我无法打开其中的流。

HANDLE indexHandle = CreateFile (indexFileName, GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ, 0, 
        OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, 0);

bool indexLock = false;
OVERLAPPED overlapped;
memset (&overlapped, 0, sizeof (overlapped));
while (noOfTries >0 && !indexLock)
{
   if (!LockFileEx (indexHandle, LOCKFILE_EXCLUSIVE_LOCK, 0, 0, UINT_MAX, &overlapped))
   {
      InfoLog << "Failed to get lock on index file  -- Error code is ["
            << GetLastError () <<"]"<<std::endl;
      Sleep(sleepTime);
      noOfTries--;

   }
   else
   {
      indexLock=true;    
   }
}

获取锁后，我想这样做:

string indexFile = mPath + Util::PATH_SEPARATOR + mIndexFileName;
os.open( indexFile.c_str(), ios_base::app);
if (!os)
{
  InfoLog << "BinaryFileSystemObjectStore:: ofstream: Failed to open index for write: " << indexFile.c_str() << endl;
}

我这样做是因为我发现使用流逐行阅读更容易...

有解决办法吗？

Answer 1

来自documentation for LockFileEx :

If the locking process opens the file a second time, it cannot access the specified region through this second handle until it unlocks the region.

因此您需要使用已有的句柄，而不是创建一个新句柄。

_open_osfhandle函数允许您从现有句柄创建文件描述符，然后您可以将此文件描述符传递给 ofstream constructor而不是文件名。