C++ Windows Asynch IO Named Pipe first message not received

Question

Modified code from Named Pipe Server Using Overlapped I/O https://msdn.microsoft.com/en-us/library/windows/desktop/aa365603(v=vs.85).aspx

The server code is as follo

Answer 1

In the server's read loop, you are discarding any data that arrives asynchronously.

After GetOverlappedResult() has reported that the pending I/O operation is complete, the buffer contains the data from that operation. You're ignoring that data and issuing a new read operation into the same buffer.

The only reason you get any of the messages is that (on most runs) all four messages will be written into the pipe's internal buffer at the same time. The first message arrives asynchronously, so you miss it, but the remaining three messages are already in the pipe so those reads can complete immediately.