[Xenomai] Fwd: RTDM !xnpod_unblockable_p() question

Philippe Gerum rpm at xenomai.org
Thu Aug 14 09:20:50 CEST 2014


On 08/14/2014 09:02 AM, Michael Smith wrote:
> On Wed, Aug 13, 2014 at 10:04 PM, Gilles Chanteperdrix <
> gilles.chanteperdrix at xenomai.org> wrote:
> 
>> On 08/13/2014 02:28 PM, Michael Smith wrote:
>>> but there is just not enough information in the code
>>> or documentation for me to solve it.
>>
>> Actually, the information can very well be found in the source code.
>>
>> #define xnpod_unblockable_p() \
>>     (xnpod_asynch_p() || xnthread_test_state(xnpod_current_thread(),
>> XNROOT))
>>
>> If you had digged a bit, you would have found that the failing test was
>> !xnthread_test_state(xnpod_current_thread(), XNROOT)
>>
>> Which clearly means that you were calling rtdm_mutex_lock() from the
>> context of the root thread and that the root thread is unblockable.
>>
>> Now, if you do not understand what the root thread is, or why it can
>> not be suspended from Xenomai's scheduler point of view, clearly, there
>> are a thing or two you have not taken the time to understand about
>> Xenomai. So, please do not reverse the roles: you are the one who has
>> not read enough documentation, please do not accuse us of not having
>> written enough.
>>
>> --
>>                                                                 Gilles.
>>
> 
> Hi Gilles
> You have misunderstood the meaning of my email.
> It was in no way a stab at the documentation of Xenomai, or the work that
> anybody has done.
> I have gone down to that level of the code up the the XNROOT definition,
> believe me I have spent hours
> scouring the existing documentation as well as the code, as well as mailing
> lists.
> So I have not come into this with no understanding.
> All I asked was for an explanation of a portion I did not understand.
> And as Philipe explained "By "kernel based task", the doc always implicitly
> means kernel-based
> _Xenomai_ task" I did not know about that assumption, maybe it is something
> that
> is obvious if you have coded the Xenomai source code for years, for me it
> was not.
> 

The Xenomai 2 doc is misleading to newcomers discovering the charms of
dual kernel systems. As a matter of fact we used to assume that dual
kernel mode was the main context, regular linux mode being the ancillary
one for installation and other housekeeping chores.

Xenomai 3 introduced context tags in the documentation which should fix
this, partly because for most APIs the dual-kernel vs native kernel
distinction does not stand anymore.

-- 
Philippe.




More information about the Xenomai mailing list