Re: [Xenomai-help] Native API rt_pipe_monitor() call can not be called from an RT Task in linux userspace ?

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

Peter Soetens wrote:
> On Wed, Jun 17, 2009 at 10:09, Philippe Gerum<rpm@xenomai.org> wrote:
>> As you have probably understood already, building a full real-time to
>> real-time data path using pipes is not possible; this said, this is not
>> the purpose of this API anyway, which has been designed for real-time to
>> non-RT communication.
> 
> I was hoping to use rt_pipe + select in real-time context to implement
> a data receiving server for real-time inter-process communication. Is
> this possible ?

No, currently, select works with posix skin descriptors and RTDM
descriptors, and rt-pipes is a native skin interface, both were not
meant to be mixed.

So, there are several ways to fix this:
- add a mapping of the xnpipe API to the posix skin (or RTDM), I do not
really know how to do this, probably the best thing would be a special
kind of socketpair, which returns both descriptors;
- add a mapping of the xnselect API to the native skin, this would allow
us the freedom to implement an interface without the long scan of the
fd_set in application which scales badly, though scalability may not be
an issue with select due to the limit of 1024 descriptors;
- have a great unified file descriptor support, which would allow to mix
interfaces.

> What would happen if the real-time clients open the pipes as rt_pipes
> and start sending
> data in ? What's the alternative to listen in real-time to many
> connections from
> a single thread ?
> 
> Peter
> 
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-- 
                                          Gilles