Re: [Xenomai-help] Communication between RT and non-RT thread

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

On 07/06/2011 11:25 AM, Andrey Nechypurenko wrote:
> Hi Folks,
> 
> In my application I have Xenomai thread which collects and process
> sensor data. In addition, I have non-RT thread which sends sensor data
> over the network for visualization (with much lower time resolution,
> picking let's say every 100th sample). Xenomai thread is the only one
> which access sensors so there is a need to pass some samples to the
> non-RT communication thread. Basically, It is a typical
> producer/consumer situation which could be solved with thread-safe
> queue. Obviously, introducing such queue with standard synchronization
> mechanisms such as mutexes, etc. is not an option since it will
> influence the RT thread which will be forced to wait for non-RT
> thread.

You can use mutexes with priority inheritance to avoid this issue. But 
Xenomai has ready made queues for rt/non-rt communication, the rtipcs:

http://www.xenomai.org/documentation/xenomai-head/html/api/group__rtipc.html



> While searching for the solution, I came to conclusion that lock-free
> [1] queue implementation is the way to go. Searching for such
> implementation which is also mature enough for real-life applications
> and works on ARM, the only one I found was boost_lockfree [2] . It is
> a great library, but it depends on boost, which in turns by default
> pulls Python and a lot of other things which are not necessary
> required on the embedded system (I am using BeagleBoard with Anstrom
> Linux distribution).
> 
> I think, the situation I have (RT supplier/non-RT consumer) is quite
> typical and I hope there should be a typical good solution for it.

A lockless solution for this (one consumer, one producer) is the good 
old fifo.

-- 
                                                                Gilles.