Date: Fri, 19 Jul 2013 01:55:46 -0400 (EDT) From: Daniel Eischen <deischen@freebsd.org> To: Joe Marcus Clarke <marcus@marcuscom.com> Cc: Koop Mast <kwm@rainbow-runner.nl>, freebsd-threads@freebsd.org Subject: Re: Mutexes and error checking Message-ID: <Pine.GSO.4.64.1307190152440.25756@sea.ntplx.net> In-Reply-To: <Pine.GSO.4.64.1307182144030.23634@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>
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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. Test program was updated: http://people.freebsd.org/~deischen/mutex_test.c -- DE
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