Question

I use a named pipe and I want to reuse the same pipe on the server to allow connecting another client once the original client has disconnected. What I do is:

• server creates a pipe using CreateNamedPipe
• server writes data using WriteFile, and retries doing so as long as error ERROR_PIPE_LISTENING is returned (which is before any client is connected)
• clients connects using CreateFile
• client reads data
• client close pipe handle using CloseHandle
• at this point server gets error ERROR_NO_DATA when it attemps to write more data
• server disconnects the pipe using DisconnectNamedPipe, which I hoped should make it free again
• server tries writing data, gets error ERROR_PIPE_NOT_CONNECTED, it retries doing so until there is no error
• however, when new client connects, and attempts CreateFile on the pipe, it gets ERROR_PIPE_BUSY

Hence, my question is: what other steps I need to do to disconnect client from the pipe properly so that a new client can connect?

Answer 1

Experimenting with various calls, I have found following to work fine:

In reaction to ERROR_PIPE_NOT_CONNECTED, server should perform:

  // allow connecting, no wait
  DWORD mode = PIPE_NOWAIT;
  SetNamedPipeHandleState(_callstackPipe,&mode,NULL,NULL);
  ConnectNamedPipe(_callstackPipe,NULL);
  mode = PIPE_WAIT;
  SetNamedPipeHandleState(_callstackPipe,&mode,NULL,NULL);

ConnectNamedPipe makes the pipe connectable (not busy) again.

Note: pipe state is changed temporarily to PIPE_NOWAIT, as otherwise ConnectNamedPipe blocks the server thread waiting for the client infinitely.

Other solution could probably be to close the handle completely on the server side and open it again.