Duplex named pipe hangs on a certain write

Question

I have a C++ pipe server app and a C# pipe client app communicating via Windows named pipe (duplex, message mode, wait/blocking in separate read thread).

It all works fi

Answer 1

I think you may be running into problems with named pipes message mode. In this mode, each write to the kernel pipe handle constitutes a message. This doesn't necessarily correspond with what your application regards a Message to be, and a message may be bigger than your read buffer.

This means that your pipe reading code needs two loops, the inner reading until the current [named pipe] message has been completely received, and the outer looping until your [application level] message has been received.

Your C# client code does have a correct inner loop, reading again if IsMessageComplete is false:

do
{
    len += mPipeStream.Read(buffer, len, buffer.Length);
} while (len>0 && !mPipeStream.IsMessageComplete);

Your C++ server code doesn't have such a loop - the equivalent at the Win32 API level is testing for the return code ERROR_MORE_DATA.

My guess is that somehow this is leading to the client waiting for the server to read on one pipe instance, whilst the server is waiting for the client to write on another pipe instance.