[Xenomai] non-blocking rt_task_suspend(NULL)

Gilles Chanteperdrix gilles.chanteperdrix at xenomai.org
Wed Apr 16 14:26:32 CEST 2014

On 04/16/2014 02:22 PM, Petr Cervenka wrote:
>> Od: Gilles Chanteperdrix <gilles.chanteperdrix at xenomai.org>
>> CC: "Xenomai" <xenomai at xenomai.org> On 04/15/2014 02:42 PM, Petr
>> Cervenka wrote:
>>> Hello I have a problem with the rt_task_suspend(NULL) call. I'm
>>> using it for synchronization of two (producer / consumer like)
>>> tasks. 1) When the consumer task has no work to do, it stops
>>> itself by calling of the rt_task_suspend(NULL). 2) When the
>>> producer creates new work for consumer, it wakes it up by calling
>>> of rt_task_resume(&consumerTask). The problem is, that consumer
>>> seldom switches to a state, that it sleeps by rt_task_suspend no
>>> more. And the task then takes all the CPU time. The return code
>>> is 0. But I already have seen couple of -4 (-EINTR) values in the
>>> past also. Consumer task status was 00300380 before and 00300184
>>> (if there is small safety sleep present). I can use for example
>>> RT_EVENT variable instead, but I'm curious if you by chance don't
>>> know, what is happening? Xenomai 2.6.3, Linux 3.5.7
>> Could you post the example of code you are using to get this
>> issue?
> It's and application with many threads, mutexes and others. It's also
> special measuring HW dependent. I can post here some simplified
> example. But I don't think it would be possible to reproduce the same
> behavior easily. It happens in my configuration only probably once
> per day and very unpredictably. But I have more details. I replaced
> rt_task_suspend / rt_task_resume by rt_event_wait / rt_event_signal.
> It failed similar way, but this time the result of wait was -4
> (-EINTR). And (after several millions of invocations) it recovered
> itself.

-EINTR is a valid return value for both rt_event_wait and 
rt_task_suspend. In case you get this error, you should loop to call 
rt_event_wait again, and not call rt_event_clear, as you risk clearing 
an event which has been signaled afterwards.


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