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

[Adhemerval Zanella <adhemerval dot zanella at linaro dot org>]

On 13/07/2018 10:04, Florian Weimer wrote:
> 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.

That is what I am not sure, if mixing POSIX semantic with C11 is really
defined by any standard (for instance, calling pthread_cancel with an
POSIX thread ID which was not created by pthread_create).

> 
>> 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.

Right, I will change thrd_sleep to use a cancellation entrypoint. We
can evaluate the POSIX cancellation interaction with C11 threads in
next releases.