[PATCH 6/6] nptl: Make pthread_{clock, timed}join{_np} act on all cancellation (BZ 33717)

[Adhemerval Zanella Netto]

On 12/12/25 16:40, Florian Weimer wrote:
> * Adhemerval Zanella:
> 
>> The pthread_join/pthread_timedjoin_np/pthread_clockjoin_np will not act
>> on cancellation if 1. some other thread is already waiting on the 'joinid'
>> or 2. If the thread has already exited.
> 
> 1. is undefined, so only 2 is relevant.
> 
>> diff --git a/nptl/pthread_join_common.c b/nptl/pthread_join_common.c
>> index 6cdb710bc9..ddf10133c1 100644
>> --- a/nptl/pthread_join_common.c
>> +++ b/nptl/pthread_join_common.c
>> @@ -28,6 +28,9 @@ __pthread_clockjoin_ex (pthread_t threadid, void **thread_return,
>>                          const struct __timespec64 *abstime,
>>                          bool cancel)
>>  {
>> +  if (cancel)
>> +    __pthread_testcancel ();
>> +
>>    struct pthread *pd = (struct pthread *) threadid;
> 
> Should pthread_tryjoin_np, pthread_clockjoin_np be a cancellation
> points?  For pthread_clockjoin_np yes, but it's more complicated for
> pthread_tryjoin_np.

The pthread_clockjoin_np is already a cancellation entrypoint and I
think it makes sense to do so (as per POSIX below).

> 
> Any thoughts on that?  We could avoid making it a cancellation point
> because pthread_tryjoin_np can never block.  So applications that need
> to act upon cancellation probably already call pthread_testcancel.

POSIX rationale to specify a cancellation entrypoint is [1]:

  Typically, only those routines that may block or compute indefinitely 
  need to include cancellation points.

Currently pthread_tryjoin_np should not block: __pthread_clockjoin_ex
will always be called when the thread is already terminated (pd->tid
equal to 0).

And since it is being marked as __THROW since its inception, I don't
think making it a cancellation entrypoint will align with POSIX or
improve things here.

And I think to make is cancellation entrypoint would require a new 
symbol version.

[1] https://pubs.opengroup.org/onlinepubs/9799919799/

> 
>> diff --git a/nptl/tst-cancel34.c b/nptl/tst-cancel34.c
>> new file mode 100644
>> index 0000000000..ad050c1dbb
>> --- /dev/null
>> +++ b/nptl/tst-cancel34.c
> 
>> +static int
>> +do_test (void)
>> +{
>> +  do_test_common (pthread_join);
>> +  do_test_common (pthread_timedjoin_np_wrapper);
>> +  do_test_common (pthread_clockjoin_np_wrapper);
> 
> Please test pthread_tryjoin_np as well.

I excluded pthread_tryjoin_np because it is not a cancellation entrypoint.

> 
> Thanks,
> Florian
>