Date: Sun, 21 Jul 2013 00:08:36 -0400 From: Joe Marcus Clarke <marcus@marcuscom.com> To: Daniel Eischen <deischen@freebsd.org> Cc: Koop Mast <kwm@rainbow-runner.nl>, freebsd-threads@freebsd.org Subject: Re: Mutexes and error checking Message-ID: <51EB5EC4.6050802@marcuscom.com> In-Reply-To: <Pine.GSO.4.64.1307190152440.25756@sea.ntplx.net> References: <51E71D4F.5030502@marcuscom.com> <Pine.GSO.4.64.1307181059460.22570@sea.ntplx.net> <51E8061B.60906@marcuscom.com> <Pine.GSO.4.64.1307181118100.22570@sea.ntplx.net> <Pine.GSO.4.64.1307182144030.23634@sea.ntplx.net> <Pine.GSO.4.64.1307190152440.25756@sea.ntplx.net>
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On 7/19/13 1:55 AM, Daniel Eischen wrote: > On Thu, 18 Jul 2013, Daniel Eischen wrote: > >> On Thu, 18 Jul 2013, Daniel Eischen wrote: >> >>> On Thu, 18 Jul 2013, Joe Marcus Clarke wrote: >>> >>>> On 7/18/13 11:09 AM, Daniel Eischen wrote: >>>>> On Wed, 17 Jul 2013, Joe Marcus Clarke wrote: >>>>> >>>>>> It seems we might have a discrepancy between the way our pthread >>>>>> implementation works compared to Linux. If a mutex is set to NORMAL >>>>>> type and one goes to unlock it, EPERM is returned unless the current >>>>>> thread is the mutex owner. While this sounds perfectly sane, it >>>>>> appears >>>>>> Linux only returns EPERM if the mutex type is ERRORCHECK. >>>>>> >>>>>> We are seeing some problems in ported code because of this. As a >>>>>> suggestion, if people agree, would it be possible to emulate the >>>>>> behavior of Linux and only return EPERM if the mutex is of type >>>>>> ERRORCHECK or RECURSVIE? >>>>> >>>>> First, any software that does that is broken. >>>>> >>>>> Second, the POSIX spec seems to imply that an error is returned >>>>> when a different thread tries to unlock an already locked mutex: >>>>> >>>>> >>>>> http://pubs.opengroup.org/onlinepubs/9699919799/functions/pthread_mutex_lock.htm >>>>> >>>>> >>>>> >>>>> Is the mutex robust or not robust? If not robust >>>>> (PTHREAD_MUTEX_STALLED), then a PTHREAD_MUTEX_NORMAL mutex >>>>> cannot be unlocked by any other thread than the owner. >>>>> So, it would seem to be wrong to _not_ return an >>>>> error when the mutex is not unlocked after >>>>> pthread_mutex_unlock() returns. >>>>> >>>> >>>> Don't get me wrong, I agree with you. This behavior should result in >>>> EPERM. However, my comment was more on the portability side to >>>> maintain >>>> parity with Linux in order to support the 3rd party code people wanting >>>> to run on FreeBSD. We can workaround it in some cases, but I was >>>> floating up to you guys to perhaps create a broader workaround. >>> >>> If it is not a robust mutex, the behavior _is_ undefined, so I >>> think Linux is allowed to return 0 (no error), just as FreeBSD >>> is allowed to return an error. I will check Solaris 10 later >>> to see what it does. >> >> I tried Solaris 10. For an already locked PTHREAD_MUTEX_NORMAL >> mutex: > > Ugh! I misread the problem when I tried to recreate it and > test it on Solaris, so forget that last email. > > It seems Solaris behaves like Linux with PTHREAD_MUTEX_NORMAL > and _unlocking_ mutexes owned by other threads (dead or not). > Solaris only returns EPERM for PTHREAD_MUTEX_ERRORCHECK > mutexes. Given that, should we do the same? Joe > > Test program was updated: > > http://people.freebsd.org/~deischen/mutex_test.c > -- PGP Key : http://www.marcuscom.com/pgp.asc
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