From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4936E5EB.9080404@domain.hid> Date: Wed, 03 Dec 2008 21:02:51 +0100 From: Gilles Chanteperdrix MIME-Version: 1.0 References: <493306F5.2080605@domain.hid> <49330CD3.4090700@domain.hid> <4933BAE2.3000502@domain.hid> <4933F1A4.8060209@domain.hid> <4933F18F.7080103@domain.hid> <4933FE5A.5060501@domain.hid> <49355B5D.8070802@domain.hid> <49355A59.4050600@domain.hid> <49357C02.1090001@domain.hid> <49365C69.5040807@domain.hid> <49366B2B.4050705@domain.hid> <493689EB.8000300@domain.hid> <4936C9CA.1090507@domain.hid> <4936C897.1000406@domain.hid> <4936D1E7.4070006@domain.hid> <4936D0B9.6070102@domain.hid> <4936D63F.50501@domain.hid> <4936D63B.3050603@domain.hid> <4936DBC1.6030303@domain.hid> <4936DBC6.9080805@domain.hid> <4936E5EA.1060008@domain.hid> In-Reply-To: <4936E5EA.1060008@domain.hid> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai-help] pthread cancelation and scheduling magics List-Id: Help regarding installation and common use of Xenomai List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Wolfgang Grandegger Cc: xenomai-help Wolfgang Grandegger wrote: > Gilles Chanteperdrix wrote: >> Wolfgang Grandegger wrote: >>> Gilles Chanteperdrix wrote: >>>> Wolfgang Grandegger wrote: >>>>> Gilles Chanteperdrix wrote: >>>>>> Wolfgang Grandegger wrote: >>>>>>> Gilles Chanteperdrix wrote: >>>>>>>> Wolfgang Grandegger wrote: >>>>>>>>> Running under gdb shows: >>>>>>>>> >>>>>>>>> Program received signal SIGSEGV, Segmentation fault. >>>>>>>>> [Switching to Thread 0x4885d4b0 (LWP 1127)] >>>>>>>>> 0x0ff49100 in pthread_cancel () from /lib/libpthread.so.0 >>>>>>>>> (gdb) where >>>>>>>>> #0 0x0ff49100 in pthread_cancel () from /lib/libpthread.so.0 >>>>>>>>> #1 0x10001d64 in ctrl_func (parm=0x0) at cancel-test.c:104 >>>>>>>>> #2 0x0ffa98e4 in __pthread_trampoline () >>>>>>>>> from /home/wolf/xenomai/lib/libpthread_rt.so.1 >>>>>>>>> #3 0x0ff42a6c in start_thread () from /lib/libpthread.so.0 >>>>>>>>> #4 0x0fdd18a0 in clone () from /lib/libc.so.6 >>>>>>>>> Backtrace stopped: previous frame inner to this frame (corrupt stack?) >>>>>>>>> >>>>>>>>> Is pthread_cancel used from the Linux pthread library? And >>>>>>>>> pthread_testcancel() as well? >>>>>>>> Yes, and I guess, as you said, that it happens because calc_func is dead >>>>>>>> when you try and cancel it. >>>>>>> Yep, but it should not crash. >>>>>> The spec says: >>>>>> The pthread_cancel() function may fail if: >>>>>> >>>>>> [ESRCH] >>>>>> No thread could be found corresponding to that specified by the >>>>>> given thread ID. >>>>>> >>>>>> >>>>>> So, it is a "may", returning ESRCH, as Xenomai does in kernel-space, is >>>>>> not mandatory. >>>>> I also got the return value ESRCH in another test. Nevertheless, a crash >>>>> is not the expected behaviour, to say the least. Here pthread_cancel() >>>>> obvoiusly get's interrupted and the calc_thread continues. Is it >>>>> possible that pthread_cancel() switches to secondary mode? >>>> pthread_cancel switches to secondary mode if it has to send a signal (if >>>> cancellation is in asynchronous mode, this happens when the target >>>> thread is blocked inside a blocking call). But this should not be a >>>> problem with RPI. >>> I disabled priority coupling in the kernel and it did not help or harm. >>> This test uses PTHREAD_CANCEL_DEFERRED, which is also the default, if >>> I understood correctly. >> You should definitely enable priority coupling. Even if you use >> PTHREAD_CANCEL_DEFERRED, when you call a blocking call, the cancellation >> is switched for the time of the blocking call to asynchronous. But since >> you do not call any blocking call, I agree that pthread_cancel should >> not switch to secondary mode, it should just set a bit in some TCB >> attached to the target thread. >> >>>> But the problem you should focus on is why the scheduler does not let >>>> pthread_cancel run earlier. >>> Don't know what you mean. The calc_func gets preempted and the ctrl_func >>> calls pthread_cancel as expected... >>> >>> calc_func: at count 20 >>> calc_func: at count 21 >>> calc_func: at count 22 >>> ctrl_func: cancel at count 23 >>> ^^^^^^^^^ >>> calc_func: at count 23 >>> >>> But then it stops somehow in pthread_cancel and calc_func continues to run. >> Yes, but since "ctrl_func: stopped at count 23" does not appear, it >> means that ctrl_func is somehow blocked in pthread_cancel. >> >> Does the test work if calc_func calls nanosleep instead of >> create_load_100ms ? > > Yes. So, pthread_cancel works even for threads running in primary mode, when they issue xenomai syscalls. > > I'm getting closer now, I think, I hope. pthread_cancel seems only to > work if calc_thread runs in secondary mode. If I set policy and priority > at the beginning of the thread function, nor pthread_setschedparam nor > clock_gettime switches to primary mode and therefore calc_thread runs in > secondary mode. If I add explicit > pthread_set_mode_np(0, PTHREAD_PRIMARY), pthread_cancel is not able to > terminate the calc_thread anymore, even with pthread_testcancel. That is not expected. But this brings me back to my initial question, do you have to work with a real world application that runs without issuing any syscall ? -- Gilles.