README file of POSIX Message Queues component.

Written by Sergio Saez <ssaez@disca.upv.es>

Copyright (C) [April 2003] OCERA Consortium.

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation version 2.
 
Description:  
 
UNIX systems offers several possibilities for interprocess communication: signals, pipes
and FIFO queues, shared memory, sockets, etc. In RTLinux, the most flexible one is
shared memory, but the programmer has to use alternative synchronisation mechanism
to build a safe communication mechanism between process or threads. On the other
hand, signals and pipes lack certain flexibility to establish communication channels 
between process.

In order to cover some of these weaknesses, POSIX standard proposes a message passing
facility that offers:
· Protected and synchronised access to the message queue. Access to data stored
  in the message queue is properly protected against concurrent operations.
· Prioritised messages. Processes can build several flows over the same queue, and
  it is ensured that the receiver will pick up the oldest message from the most urgent
  flow.
· Asynchronous and temporised operation. Processes have not to wait for operation to 
  be finish, i.e., they can send a message without having to wait for someone to
  read that message. They also can wait an specified amount of time or nothing at all, if
  the message queue is full or empty.
· Asynchronous notification of message arrivals. A receiver process can configure
  the message queue to be notified on message arrivals. So such a process can be
  working on something else until the expected message arrives.

Related keywords: Real-Time, POSIX, communication, IPC