From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4AF22E85.50400@domain.hid> Date: Thu, 05 Nov 2009 02:46:45 +0100 From: Gilles Chanteperdrix MIME-Version: 1.0 References: <634c78ce0910010730t29137af8w95b63ae21183b52b@domain.hid> In-Reply-To: <634c78ce0910010730t29137af8w95b63ae21183b52b@domain.hid> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai-core] select: native tasks with posix skin mqueues List-Id: Xenomai life and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Soetens Cc: Xenomai core Peter Soetens wrote: > Hi, > > I'm creating my RT threads using the native API and I'm creating > mqueues, wrapped to the pthread_rt library. > I can read and write the mqueue (and it goes through Xenomai), but > when I select() on a receiving mqd_t, the select() calls returns that > there is data available on the mq (it fills in the FD_SET), but keeps > doing so even when it's empty (the select() is in a loop). Also, it's > modeswitching like nuts. > > I found out that the __wrap_select is correctly called, but returns > -EPERM. Kernel sources indicate that this is caused by > pse51_current_thread() alias thread2pthread() returning null. Since > EPERM is returned to userspace, the __real_select is called from user > space, causing the mode switches and bad behaviour. This is almost > certainly the thing that native + RTDM + select() is seeing too. > > My mqueues-only work probably because mq.c only uses > pse51_current_thread() in the mq_notify function. I'm guessing that > mq_notify would also not work in combination with native skin. > > I had two options in fixing this: add a xnselector to the native task > struct or to the nucleus xnthread_t. I choose the latter, such that > every skin kan use select() + RTDM and migrate gradualy to the RTDM > and/or Posix skin. > I needed to free the xnselector structure in xnpod_delete_thread() , I > chose a spot, but it causes a segfault in my native thread (which did > the select) during program cleanup. Any advice ? Also, maybe we should > separate select() from the posix skin and put it in a separate place > (in RTDM as rtdm_select() ?), such that we can start building around > it (posix just forwards to rtdm_select() then). > > A second patch was necessary to return the timeout case properly to > userspace (independent of first patch). > > Tested with native + posix loaded and mq. If you never quit your > application, this works :-) Hi, I have included a lightly modified version of this patch on head, I do not see any crash. However, I have some doubts about the current implementation: calling xnselector_destroy() opens opportunities for a rescheduling, which I am not sure is really what we want in the middle of xnpod_delete_thread(). Philippe, what do you think? Regards. -- Gilles.