[vlc-devel] [RFC 0/2] New executor API

[Rémi Denis-Courmont]

Le torstaina 27. elokuuta 2020, 18.50.29 EEST Romain Vimont a écrit :
> On Thu, Aug 27, 2020 at 05:47:49PM +0300, Rémi Denis-Courmont wrote:
> > Le torstaina 27. elokuuta 2020, 17.32.10 EEST Romain Vimont a écrit :
> > > Yes, but vlc_executor_Cancel() may "interrupt" the task at any time, so
> > > you have to handle it anyway (timeout or not).
> > 
> > That's never going to work, unless the runnable has its own killable
> > process (which should be had for other reasons, notably I/O scheduling).
> 
> I don't understand why you say it can't work.

You simply can't stop another thread arbitrarily.

You can use thread cancellation, if the threaded code supports it - but most 
likely it doesn't, and there is a lack of static analysis support to verify 
basic cancellation mistakes.

Again, it's much much easier and less error-prone to have a time-out within 
the thread.

> Canceling a runnable does work. This is already what
> background_worker_Cancel() provides, and with the vlc_executor_t it
> calls the interrupt() callback:

Unless the runnable is trivial and spends all its time waiting on a single 
"thing", it simply won't work.

It also won't work if the runnable is I/O bound, as there are no sane ways to 
interrupt poll() in library code, even less read/recv and write/send 
functions. You can cancel poll(), or you can send a thread signal, but 
libraries have no ways to reserve a signal for their own use.

-- 
Реми Дёни-Курмон
http://www.remlab.net/