How to make a good asyncrhronous comunication.

[José Antonio Sánchez]

I need to comunicate two processes but I only want to write complete
messages. The problem with a FIFO is that you can write half of a
message without error. With a mailbox you have the r_mbx_send_if so,
if there is no space to write the whole message, nothing is written to
the mailbox, but I can't find something similar in a FIFO.
On the other hand, I have to comunicate my real time application with
a GUI process (made in QT), so I have to get the data asynchronously
to let the GUI receive mouse events. That could be made with a FIFO in
real time and a QSocketNotifier in the user space. But, Is there a way
to make something similar with a mailbox? How?
Thanks.