From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4936E5EA.1060008@domain.hid> Date: Wed, 03 Dec 2008 21:02:50 +0100 From: Wolfgang Grandegger 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> In-Reply-To: <4936DBC6.9080805@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: Gilles Chanteperdrix Cc: xenomai-help 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. 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. Wolfgang.