Re: [PATCH v8 1/8] nptl: Add C11 threads thrd_* functions

[Florian Weimer <fweimer at redhat dot com>]

On 07/13/2018 02:59 PM, Adhemerval Zanella wrote:
> On 13/07/2018 06:45, Florian Weimer wrote:
> > On 02/02/2018 06:04 PM, Adhemerval Zanella wrote:
> > >     2. thrd_sleep uses nanosleep internal direct syscall to avoid clobbering
> > >        errno, to handle expected standard return codes, and to avoid making
> > >        the call a POSIX cancellation entrypoint.
> >
> > Isn't this inconsistent with the conditional variable wait and thread join functions, which are still cancellation points?
> >
> > On the other hand, a sleep function which is not a cancellation point may be useful.
>
> I am not sure which would be the best option to handle POSIX cancellation
> with C11 threads with nptl implementation. Most straightforward option is
> just use cancellation entrypoints as default, even though using thread
> cancellation in C11 is UB (there is no defined way the use can get the
> POSIX thread id from a C11 thread).

That's not true.  The POSIX thread ID is available using pthread_self on 
the thread itself, and that can be passed to another thread.

> Another option is just disable cancellation by using non-cancellable
> entry-points and/or explicit disable cancellation.  For thrd_join is
> just a matter to set on '__pthread_timedjoin_ex', but for
> cnd_wait/cnd_timedwait we either need to explicit enable/disable or
> add an option to __pthread_cond_wait_common to select whether to use
> cancellable syscalls.

From my point of view, the least surprising approach would be to make 
thrd_sleep a cancellation point to match nanosleep.

Thanks,
Florian