Re: Replacement for Xenomai's Message queues?

[Darren Hart <dvhltc@us.ibm.com>]

M. Koehrer wrote:
> Hi all,
> 
> I am about to switch an realtime application from Xenomai to the RT_PREEMPTION patch.
> Everything works really smooth, however I have one question.
> With my Xenomai application I use the message queue which combine transfer (including queuing)
> of data with activation of the thread.
> In my Xenomai application I use this feature quite frequently. Now, I am not sure how to do an equivalent
> with the RT_PREEMPT patch.
> (see http://www.xenomai.org/documentation/xenomai-2.4/html/api/group__native__queue.html)
> Of course I could use condition variables and a struct or array to hold the data I want to pass with the activation
> of a thread. However, using this approach I do not have the queuing (which is some extra effort I could spent...).
> Another idea I have: I could use sockets which realize the queuing but the overhead is too high.
> 
> Is there any suitable way to implement a message queue like approach using RT_PREEMPT patch?
> I am running x86 (Dual/Quad Cores).

I don't if we have many xenomai experts on this list. It would help to 
understand which aspects of the Xenomai message queue are important to 
you (other than the ability to block on a queue and wake when a message 
is available). For a basic message queueing system with the ability to 
prioritize messages, you can look to the POSIX.4 Message Queues. A 
google search will provide plenty of howto's, and the API appears at 
least similar to what you were using with Xenomai.

I haven't looked, but I don't think Linux supports message driven 
Priority Inheritance 
(http://www.qnx.com/developers/docs/6.3.2/neutrino/sys_arch/kernel.html#Priority_inheritance_messages).

-- 
Darren Hart
IBM Linux Technology Center
Real-Time Linux Team