Re: [Xenomai-help] Question about getting system time

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

Jan Kiszka wrote:
> Steve Deiters wrote:
>> I guess that is my point though.  Not being all too familiar with the
>> inner workings of Linux or glibc, how am I supposed to know which
>> services are not emitting a syscall?  I accept that I will lose
>> determinism in calling these services, but I find it odd that it may
>> allow the system to deadlock.
>>
>> If nothing else the syscall-less services should be listed and noted as
>> unsafe.  I am new to most of this, but I have went through most of the
>> documentation and, unless I have overlooked it, found nothing mentioning
>> this.
> 
> Key services that do not reliably trigger syscalls:
> 
>  - gettimeofday
>  - clock_gettime (unless the POSIX skin is in use)
>  - malloc
>  - free
> 
> There are no guarantees either, but this list turned out to be fairly
> complete while porting a large (x86) application from plain Linux to
> Xenomai. Only gettimeofday (and, conditionally, clock_gettime) suffer
> from the live-lock problem.
> 
> For runtime checks, enable T_WARNSW / PTHREAD_WARNSW for your RT
> threads, additionally link against librtdk, --wrap the above services,
> and assert_nrt() will trigger a SIGDEBUG when they are used from a RT
> thread (just like normal syscalls will do).
> 
> There should be a few more services in the glibc that trigger malloc
> internally without issuing a syscall. When you come across one (check
> the man pages), additions to xenomai/src/rtdk/assert_context.c are welcome.

Should not we make things more automatic? Integrate rtdk into libxenomai
and forcibly do the wrapping? I am also thinking about modifying
rt_print to make it possible to use it as a drop-in replacement of
printf, and wrap it when using the posix skin.

-- 
					    Gilles.