From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <493805E3.30404@domain.hid> Date: Thu, 04 Dec 2008 17:31:31 +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> <4936E5EA.1060008@domain.hid> <4936E5EB.9080404@domain.hid> <4937F76D.7040906@domain.hid> <4937F961.1080605@domain.hid> In-Reply-To: <4937F961.1080605@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: [...deletions...] >>> 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 ? >> If a add long nanosleeps, e.g. 100, 10 or 1 ms, cancellation works but >> it fails with short nanosleeps. A syscall seems not sufficient. I have >> the impression that pthread_cancel needs some time in secondary mode to > > When calling nanosleep, the threads spends on time in secondary mode. I What do you mean? nanosleep switches to secondary mode? > think the problem is rather that only asynchronous cancelation (meaning > cancelation with a signal) works. Setting the cancelation bit somehow > gets lost. > >> do it's duties, e.g. mark the thread as canceled. Would it make sense to >> wrap pthread_cancel, and friends to the corresponding kernel functions >> in ksrc/skins/posix? >> Is there a way to force a thread switching to secondary mode? > > No, there is no way to force a thread to switch to secondary mode, the > xnshadow_relax call explicitely requires to be called by the target > thread. Before I wrap pthread_cancel, I would really like to understand > why setting a bit with pthread_cancel and testing it with > pthread_testcancel does not work. > > What is the trace of your test when run: > - on ARM > - with root thread priority inheritance, > - with USE_EXPLICIT_SCHED and USE_TEST_CANCEL, and CANCEL_TYPE set to > PTHREAD_CANCEL_DEFERRED > - posting a semaphore in ctrl_func before calling nanosleep, and waiting > for that semaphore in main before creating the calc_func thread. The calc_thread is not canceled and a segmentation fault happens. Canceling the calc_thread does *not* work if it's running in primrary mode, nor on ARM, nor on PowerPC. It does work when calc_thread does run in secondary mode, which happened with USE_EXPLICIT_SCHED not set. If you want do to some tests, I could send you my revised test program. My conclusion is that pthread_cancel can not be used to cancel busy realtime threads. I'm going to re-write the program using the native skin and rt_task_delete. >> It might happen that an application does not block due to overload. > > IMO, we do not care much about these cases, the watchdog is there to > catch them. But then pthread_cancel is not really useful. Unfortunately, this application needs some special measures to allow Linux to breath, especially in the initialization phase, e.g. with the SCHED_SPORADIC. Thanks. Wolfgang.