Re: RFC: pthread pid accessor (BZ# 27880)

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 01/06/2021 14:36, Florian Weimer wrote:
> * Adhemerval Zanella:
> 
>> I think we should return the TID while the thread is being executing
>> either cancellation handler or c++ destructors during the unwind 
>> phase. Once no more user defined callback are being executed we should
>> not return the TID anymore.
> 
>>> Yes, I would prefer that.  Does Bionic return the TID from the
>>> resettable TCB field, or a copy?
>>
>> Bionic seems to maintain a list of active threads, so it returns
>> the active thread field directly.
> 
> My question was whether Bionic implements that exit behavior, or
> something else.
> 

If I understood correctly bionic implementation will just dissociate
the thread from the global thread list *after* it has been joined by
pthread_join.  It basically does:

  pthread_join
    thread = find_in_global_list

    old_state = THREAD_NOT_JOINED
    while (!cas (thread->join_state, &old_state, THREAD_JOINED))

    if (thread->tid != 0)
      futex_wait (&thread_tid, 0)

    remove_from_global_list (thread)

And the pthread assessor is basically:

  pthread_gettid
    thread = find_in_global_list
    return thread->tid