[PATCH v9] linux: Do not spawn a new thread for SIGEV_THREAD (BZ 30558, 27895, 29705, 32833)

[Florian Weimer]

* Adhemerval Zanella:

> The current timer_create SIGEV_THREAD implementation has some
> downsides:
>
>   1. There is no way to report failure at thread creation when a
>      timer triggers.  It means that it might occur unreported and with
>      missed events depending of the system load.

Error reporting can be added to the existing implementation, by
incrementing a counter on pthread_create failure and returning the sum
of this counter and the kernel counter in timer_getoverrun, I believe.

I think changing from multiple threads to a single serialized thread is
quite drastic and may not be what applications expect.  We might need
another round of compatibility symbols for that.

Thanks,
Florian