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Re: [PATCH] nptl: Remove cancellation checks from sem_{timed}wait (BZ #23006)
On 25/06/2019 10:36, Florian Weimer wrote:
> * Adhemerval Zanella:
>
>> In any case, do you think we should make sem_{timed}wait not a cancellation
>> entrypoint for 2.30? I can rework the patch if it is the case.
>
> Do we have any other form of blocking synchronization that is
> cancellable? If not, a cancellable semaphore wait operation would make
> sense. But then we should perform the cancellation check on the fast
> path, too.
pthread_cond_wait, pthread_cond_timedwait, and pthread_join as well the
gnu extension pthread_timedjoin_np and pthread_cond_clockwait (not yet
upstream). Depending of you definition of synchronization, you can also
include sigtimedwait, sigwait, sigwaitinfo, wait, waitid, and waitpid.
We explicit does not support cancellation for pthread_rwlock_rdlock,
pthread_rwlock_timedrdlock, pthread_rwlock_timedwrlock, and
pthread_rwlock_wrlock. I tend to see that pthread_rwlock_* are similar
to pthread_mutex and the rationale layout on 'Thread Cancellation
Overview' also applies.
So at least we have synchronization functions that explicit does not
act for cancellation, we might extend it to sem_{timed}wait now that
they are also listed on 'shall'.
However, I still think this does not really follow along with the
rationale exposed on the very issue that triggered it [1], which aimed
imho to just remove the requirement of check for cancellation on fast
path only.
[1] http://austingroupbugs.net/view.php?id=1076#c3938