Re: [PATCH 12/23] nptl: Introduce __nptl_deferred_init

[Florian Weimer <fweimer@redhat.com>]

* Adhemerval Zanella:

> On 13/05/2021 17:51, Florian Weimer wrote:
>> * Adhemerval Zanella:
>> 
>>> On 12/05/2021 13:58, Florian Weimer via Libc-alpha wrote:
>>>> This function is called once by pthread_create, before spawning
>>>> the first thread, and also within pthread_cancel.  Since it sets up
>>>> cancellation handlers, place it along with the pthread_cancel
>>>> implementation within libc.
>>>
>>> Why does it need to be initialized by pthread_create as well?  I think
>>> moving the initialization to pthread_cancel and only setting once
>>> when pthread_cancel is called (and not tying to __libc_single_threaded)
>>> is slight better since it avoids the setup of SIGCANCEL for programs
>>> that do not use cancellation.
>> 
>> We need to unblock SIGCANCEL anyway, so that we can send the signal.
>> This part can't be deferred until pthread_cancel is called.
>
> Yes, what it seems to be wrong is unblocking it on both pthread_create
> *and* on pthread_cancel.

We need to unblock in pthread_cancel too, to support self-cancel in a
single-threaded process.

Do you know if we ever change the signal mask to enable/disable
asynchronous cancellation?  I don't think so.  Then we could support
self-cancel simply by calling the signal handler.  (It would not matter
whether the process is multi-threaded or not.)

If we do that, I think it is simpler to do all the initialization in
pthread_create.

Thanks,
Florian