Date: Thu, 18 Jul 2013 11:22:42 -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.4.64.1307181118100.22570@sea.ntplx.net> In-Reply-To: <51E8061B.60906@marcuscom.com> References: <51E71D4F.5030502@marcuscom.com> <Pine.GSO.4.64.1307181059460.22570@sea.ntplx.net> <51E8061B.60906@marcuscom.com>
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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. How many cases of this are we seeing in ports? How hard is it to upstream portability fixes to them - are they usually willing to accept these types of fixes? -- DE
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