Bug#1099624: libc6 2.41 pthread cause pari to FTBFS

[Bill Allombert <ballombe@debian.org>]

On Mon, Mar 10, 2025 at 03:18:07PM +0100, Bill Allombert wrote:
> In that spirit, please find a third one, which fail with both libc, 
> but in a different way.
> 
> About 10% of the time, it hangs in 'exit' after all threads have terminated.

(This is an aside to this bug report, but is better to be thorough.)

For what is worth, I think I found the problem with this one test:

> static void
> mt_err_recover(void)
> {
>   if (mt_thread_no>=0)
>   {
>     struct mt_pstate *mt = pari_mt;
>     struct mt_queue *mq = mt->mq+mt_thread_no;
>     LOCK(mq->pmut)
>     {
>       mq->output = -1;
>       pthread_cond_signal(mq->pcond);
>     } UNLOCK(mq->pmut);
>     pthread_exit((void*)-1);
>   }
> }

This function is called in PTHREAD_CANCEL_ASYNCHRONOUS mode,
I am not sure calling pthread_exit with PTHREAD_CANCEL_ASYNCHRONOUS
is valid.
Adding
pthread_setcanceltype(PTHREAD_CANCEL_DEFERRED,NULL)
before LOCK seems to fix the problem.
So this one is probably a bug in PARI/GP.

Cheers,
Bill.