[vlc-devel] [PATCH 1/2] win32: add cancel functions to be called in the APC

Steve Lhomme robux4 at gmail.com
Mon Jan 18 09:28:49 CET 2016

On Sun, Jan 17, 2016 at 2:36 PM, Rémi Denis-Courmont <remi at remlab.net> wrote:
> On Sunday 17 January 2016 14:17:47 Steve Lhomme wrote:
>> On Sat, Jan 16, 2016 at 6:34 PM, Rémi Denis-Courmont <remi at remlab.net>
> wrote:
>> > On Friday 15 January 2016 17:16:21 Steve Lhomme wrote:
>> >> --
>> >> this is going to be useful to cancel socket tasks that are not alertable
>> >
>> > That makes no sense. If the waiting function cannot be alerted, the
>> > asynchronous procedure callback won´t be invoked. We already have
>> > cancellation cleanup handlers then.
>> Maybe I did not use the right term. select() does let the cancel APC
>> run. But unlike WSAWaitForMultipleEvents(), it doesn't exit (with
>> WSA_WAIT_IO_COMPLETION) when after the APC is run. So the infinite
>> wait just sits there.
>> That's why in patch 2/2 I use an extra UDP socket that is canceled
>> during the APC, thus making select() exit as we want.
> Winsock is not supposed to be re-entrant, so this is undefined.

I tried to find information on this and found nothing. But since such
information may be bogus I tested the code and it works on XP SP3 and
W10. I assume it should also work in the versions in between.

> Besides, INET sockets bring a variety of failure cases that make them
> unsuitable as a reliable intra-process wake-up mechanism.
>> This seems to be
>> a common solution:
>> http://stackoverflow.com/questions/3333361/how-to-cancel-waiting-in-select-o
>> n-windows
> Just FYI, stackoverflow.com is not exactly what I would call a reliable source
> of information. Regardless, that page suggests calling send() from *another*
> thread. Big deal.

I can also try that.

> --
> Rémi Denis-Courmont
> http://www.remlab.net/
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