Can I use a file handles in IO completion ports with and without overlapped I/O

Question

I want to use ReadFile() (overlapped) on a named pipe in message mode in combination with an I/O completion port.

So, I have multiple threads waiting for ReadFile() to receive data. The awaken thread will process the message and may call WriteFile() on another pipe handle without overlapped I/O.

I only have real small chunks. Is it possible to use a handle that is associated to an I/O completion port with WriteFile() and non-overlapped I/O?

Are there any issues that I should be aware of?

Answer 1

Is it possible to use a handle that is associated to an I/O completion port with WriteFile() and non-overlapped I/O?

no, this not possible. if handle associated to an I/O completion - this file handle opened with the FILE_FLAG_OVERLAPPED flag, and as result overlapped (asynchronous) I/O will be used for this file. maximum what you can do - prevent completion port notification. This is done by specifying a valid event handle for the hEvent member of the OVERLAPPED structure, and setting its low-order bit. A valid event handle whose low-order bit is set keeps I/O completion from being queued to the completion port. but I/O anyway will be asynchronous and in this case.

But I don't want a new message to arrive and handled between receiving and writing. So as long as I start a new Read (overlapped) and I Write the answer (non overlapped) my processes are in a "stable stage".

new message not arive until you not start new Read. so when read complete - first decide - are you need answer to message and if yes - do WriteFile - asynchronous - this not create any problem and you not need wait in place until write completed. and then start new Read.

so really you not need synchronous write on file