Getting Started with QNX Neutrino - QNX Software Systems

© 2009, QNX Software Systems GmbH & Co. KG. Using message passing
Architecture & structure
We’ve been talking about “clients” and “servers.” I’ve also used three key phrases:
• “The client sends to the server.”
• “The server receives from the client.”
• “The server replies to the client.”
I specifically used those phrases because they closely reflect the actual function names
used in Neutrino message-passing operations.
Here’s the complete list of functions dealing with message passing available under
Neutrino (in alphabetical order):
• ChannelCreate(), ChannelDestroy()
• ConnectAttach(), ConnectDetach()
• MsgDeliverEvent()
• MsgError()
• MsgRead(), MsgReadv()
• MsgReceive(), MsgReceivePulse(), MsgReceivev()
• MsgReply(), MsgReplyv()
• MsgSend(), MsgSendnc(), MsgSendsv(), MsgSendsvnc(), MsgSendv(),
MsgSendvnc(), MsgSendvs(), MsgSendvsnc()
• MsgWrite(), MsgWritev()
Don’t let this list overwhelm you! You can write perfectly useful client/server
applications using just a small subset of the calls from the list — as you get used to the
ideas, you’ll see that some of the other functions can be very useful in certain cases.
A useful minimal set of functions is ChannelCreate(), ConnectAttach(), MsgReply(),
MsgSend(), and MsgReceive().
We’ll break our discussion up into the functions that apply on the client side, and those
that apply on the server side.
The client
The client wants to send a request to a server, block until the server has completed the
request, and then when the request is completed and the client is unblocked, to get at
the “answer.”
This implies two things: the client needs to be able to establish a connection to the
server and then to transfer data via messages — a message from the client to the server
(the “send” message) and a message back from the server to the client (the “reply”
message, the server’s reply).
April 30, 2009 Chapter 2 • Message Passing 91