Re: [Qemu-devel] [PATCH] [RFC] aio/async: Add timed bottom-halves

[Alex Bligh]

Stefan,

--On 19 July 2013 09:58:50 +0800 Stefan Hajnoczi <address@hidden> 
wrote:

> >   Options:
> >
> >   a) restore alarm timers (at least for the time being). Make all
> >      alarm timers do qemu_notify_event. However, only run the AioContext
> >      clock's timers within aio_poll. This is the least intrusive change.
> >
> >   b) calculate the timeout in aio_poll with respect to the minimum
> >      deadline across all clocks, not just AioContext's clock. Use the
> >      same logic in mainloop.
> >
> >   I'd go for (b), except for the millisecond accuracy thing. So my
> >   temptation (sadly) is (a).
>
> I think this is a non-issue because host_alarm_handler() can only be
> called from the main loop:
>
> main-loop.c:qemu_signal_init() sets up signalfd to monitor SIGALRM.
> Therefore we do not asynchronously invoke the SIGALRM signals handler.
> It is only invoked from main-loop.c:sigfd_handler() when the main loop
> runs.
>
> That's how I read the code.  I haven't checked a running process to be
> sure.

Not sure that's the case on win32, but OK let's go with that.

However, I still don't quite see how the poll in the mainloop is
meant to exit when a timer expires. There's now no qemu_notify_event,
and no SIGALRM, and the timeout will still be infinite (unless I
calculate the timeout as the minimum across all clocks, in which
case I might as well do (b) above).

--
Alex Bligh