I've two threads, one that writes to a file, and one that reads from the same file. I use CreateFile & WriteFile, FlushFileBuffers in the writer thread, and the reader thread uses FtpPutFile.
How do I implement a simple windows32 Mutex here? (I haven't used it for years)
Or, is this possible with proper flags sent to CreateFile? (I tried but no luck)
You don't need a mutex. You can safely read and write to the same file in multiple threads. You can open the file more than once so that each thread has its own file handle and thus its own file pointer or you can use overlapped I/O to read or write at a specific position.
You don't need to open the file for overlapped I/O. You can just do this:
LARGE_INTEGER off = offset;
OVERLAPPED ov = { 0 };
ov.Offset = off.LowPart;
ov.OffsetHigh = off.HighPart;
ReadFile(handle, buffer, count, &bytesRead, &ov);
This allows you to read at a particular position in the file (offset) atomically, so you don't have to call SetFilePointerEx and worry about another thread messing up the pointer. The same thing works for writing.
FtpPutFile is accessing it so you don't put garbage on the server.
Commented
Aug 9, 2012 at 14:27
How to implement a simple mutex:
You create a mutex with the CreateMutex function OR CreateMutexEx. You will need to call CloseHandle when you are done with it. Once you have the mutex then you can call WaitForSingleObject to synchronize your calls (don't forget to call ReleaseMutex when you are done. Lastly, here is an example of using the Mutex object.
