Re: [Qemu-devel] experience with SDL2, event loop & main thread

["Daniel P. Berrange" <berrange@redhat.com>]

On Mon, Dec 12, 2016 at 06:36:16PM +0800, Fam Zheng wrote:
> On Mon, 12/12 12:20, Liviu Ionescu wrote:
> > 
> > > On 12 Dec 2016, at 11:39, Fam Zheng <famz@redhat.com> wrote:
> > > 
> > > ... I myself know next to nothing about SDL project.
> > 
> > ok, neither do I.
> > 
> > 
> > do you have any comments on the current situation of the SDL integration in
> > QEMU? any comments on the conclusions I reached after integrating SDL2 into
> > GNU ARM Eclipse QEMU?
> > 
> > personally I do not like at all polling the SDL loop every 10 ms on a timer,
> > but I currently have no other solution. I tried to move the I/O loop on a
> > separate thread, but the Windows implementation of `poll` works only on the
> > main thread.
> 
> Like I said ealier, instead of "polling" SDL events in a timer, how about
> registering an EventNotifier in the main thread which is notified by the vCPU
> thread upon a new graphics operation? That will fix the latency issue.

Also, note that SDL is not the only backend that requires all graphics
operations to take place in a single thread. GTK2/3 both require that
everything is done in the same thread. So if there's any parts of QEMU
that are triggering graphics operations in non-main threads, we really
need to make sure any fix applies to all QEMU graphics backends, not
just SDL2.

Regards,
Daniel
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