Re: [Xenomai] Demo example of a simple periodic thread for Xenomai (Posix API)

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

On Fri, Aug 21, 2015 at 08:53:26PM +0200, Marc Le Douarain wrote:
> Hello eveybody,
> 
> As I haven't found a little example of a periodic thread written in Posix,
> I've tried to do it.
> 
> Here you will find joined the demo files example.
> It can be (cross-)compiled for :
> - Standard Linux
> - Xenomai 2
> - Xenomai 3
> In the Makefile, comment 2 lines MY_CFLAGS & MY_LDFLAGS to compile for
> standard Linux.
> 
> Hope it can be helpfull for other people,
> and many thanks for any comments or mistakes reports on it !
> OUPPSS, JUST SEEN that XENOMAI version 3 is doing 'modes switches'... so
> there is something bad! Any idea ?
> 
> Perhaps to include a basic example like this one in the "demo" directory of
> Xenomai would be interesting!?
> 
> Best regards.
> 
> PS: I have beed disapointed at the start to discover no more
> pthread_make_periodic_np() & pthread_wait_np() functions with
> Xenomai 3.

These functions were there to help porting legacy code from RTLinux,
they were not really meant to be used in new code.

> But
> finally now with a timerfd we can have the same sourcecode with standard
> Linux, so not too bad ! ;-)
> And also no more the "__XENO__" define, but also usefull for conditional
> compilation, with the new "__COBALT__" !
> 
> 
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> Name: demo_periodic_thread_posix.c
>
> (...)
>
> int CreatePosixTask( char * TaskName, int Priority, int StackSizeInKo, unsigned int PeriodMicroSecs, void * (*pTaskFunction)(void *) )
> {
> 	pthread_attr_t ThreadAttributes;
> 	pthread_attr_init(&ThreadAttributes);
> 	pthread_attr_setdetachstate(&ThreadAttributes, PTHREAD_CREATE_DETACHED /*PTHREAD_CREATE_JOINABLE*/);
> #if defined(__XENO__) || defined(__COBALT__)
> 	pthread_attr_setschedpolicy(&ThreadAttributes, SCHED_FIFO);
> 	struct sched_param paramA = { .sched_priority = Priority };
> 	pthread_attr_setschedparam(&ThreadAttributes, &paramA);

A call to pthread_attr_setinheritsched is missing here. The default
for inheritsched is PTHREAD_INHERIT_SCHED, which means the new
thread inherits the main thread scheduling policy and priority,
which is usually SCHED_OTHER and 0 (unless you run the program with
chrt), in which case the newly created thread switches back to
secondary mode after every primary mode switch.

-- 
					    Gilles.
https://click-hack.org