Date: Wed, 7 Aug 2019 18:25:48 +0800 From: Erich Dollansky <freebsd.ed.lists@sumeritec.com> To: Daniel Eischen <deischen@freebsd.org> Cc: Konstantin Belousov <kostikbel@gmail.com>, freebsd-questions@freebsd.org, freebsd-threads@freebsd.org Subject: Re: mutex held in a thread which is cancelled stays busy Message-ID: <20190807182548.1a8e00dd.freebsd.ed.lists@sumeritec.com> In-Reply-To: <AFA42FF8-C49F-495F-BD4A-F9FBB9301F5E@freebsd.org> References: <20190806165429.14bc4052.freebsd.ed.lists@sumeritec.com> <1FC05CEB-982F-484F-9E41-5A74FF564494@freebsd.org> <20190807071002.GF2731@kib.kiev.ua> <20190807163757.2b5d52fa.freebsd.ed.lists@sumeritec.com> <20190807092035.GG2731@kib.kiev.ua> <AFA42FF8-C49F-495F-BD4A-F9FBB9301F5E@freebsd.org>
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Hi, On Wed, 7 Aug 2019 06:07:25 -0400 Daniel Eischen <deischen@freebsd.org> wrote: > > On Aug 7, 2019, at 5:20 AM, Konstantin Belousov > > <kostikbel@gmail.com> wrote: > >> On Wed, Aug 07, 2019 at 04:37:57PM +0800, Erich Dollansky wrote: > >> Hi, > >> > >> On Wed, 7 Aug 2019 10:10:02 +0300 > >> Konstantin Belousov <kostikbel@gmail.com> wrote: > >> > >>>> On Tue, Aug 06, 2019 at 08:58:30PM -0400, Daniel Eischen wrote: > >>>> > >>>>> On Aug 6, 2019, at 4:54 AM, Erich Dollansky > >>>>> <freebsd.ed.lists@sumeritec.com> wrote: > >>>>> > >>>>> Hi, > >>>>> > >>>>> for testing purpose, I did the following. > >>>>> > >>>>> Start a thread, initialise a mutex in a global variable, lock > >>>>> the mutex and wait in that thread. > >>>>> > >>>>> Wait in the main program until above's thread waits and cancel > >>>>> it. > >>>>> > >>>>> Clean up behind the cancelled thread but leave intentional the > >>>>> mutex locked. > >>>>> > >>>>> I would have expected now to get an error like 'EOWNERDEAD' > >>>>> doing operations with that mutex. But I get 'EBUSY' as the > >>>>> error. > >>>> > >>>> Are you initializing the mutex as a robust mutex, via > >>>> pthread_mutexattr_setrobust()? Are you using _lock() or > >>>> _trylock()? > >>> Robust mutexes only have special properties on the process > >>> termination. They behave same as the normal mutexes if the owning > >>> thread is terminated. > >>> > >> man says: > >> > >> [EOWNERDEAD] The argument mutex points to a robust mutex and the > >> previous owning thread terminated while holding the mutex lock. > > > > So what ? It describes the case when error can be returned, but it > > is not required to do so. POSIX wording is the following: > > > > If mutex is a robust mutex and the process containing the owning > > thread terminated while holding the mutex lock, a call to > > pthread_mutex_lock() shall return the error value [EOWNERDEAD]. If > > mutex is a robust mutex and the owning thread terminated while > > holding the mutex lock, a call to pthread_mutex_lock( ) may return > > the error value [EOWNERDEAD] even if the process in which the > > owning thread resides has not terminated. > > > > Note the difference between shall and may. We only process robust > > list on the process termination. If the process is still alive, > > but the thread terminated, it can only happen because the process > > code asked for the thread termination explicitly, and then the code > > should be able to keep its own state. On really fatal conditions, > > like unhandled signals, kernel terminates the process, not a > > thread. > > But pthread_mutex_lock() should not return EBUSY; that is only for > _trylock(). It seems to me _lock() should either return EOWNERDEAD > or EDEADLK, or it just blocks indefinitely. > > Erich, are you getting EBUSY for pthread_mutex_lock() or is that only > for pthread_mutex_trylock()? > EBUSY is only returned when I call 'pthread_mutex_trylock'. The other one just hangs. Give me a bit if time and I will send you then a test program which is extracted from my test environment. Not that the error stems from very own test environment. Erich
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