On Tue, 06 Mar 2012 07:51:29 -0600 Anthony Liguori <anth...@codemonkey.ws> wrote:
> On 03/06/2012 07:16 AM, Alon Levy wrote: > > On Tue, Mar 06, 2012 at 09:24:27AM -0300, Luiz Capitulino wrote: > >> On Tue, 06 Mar 2012 08:36:34 +0100 > >> Gerd Hoffmann<kra...@redhat.com> wrote: > >> > >>> Hi, > >>> > >>>>> How would the parallel execution facility be opaque to the implementer? > >>>>> screendump returns, screendump_async needs to pass a closure. You can > >>>>> automatically generate any amount of code, but you can only have a > >>>>> single function implementation with longjmp/coroutine, or having a > >>>>> saparate thread per command but that would mean taking locks for > >>>>> anything not trivial, which avoids the no-change-to-implementation. Is > >>>>> this what you have in mind? > >>>> > >>>> It would not be opaque to the implementer. But it would avoid > >>>> introducing new commands and events, instead we have a unified mechanism > >>>> to signal completion. > >>> > >>> Ok. We have a async mechanism today: .mhandler.cmd_async = ... > >>> > >>> I know it has its problems like no cancelation and is deprecated and > >>> all. But still: how about using it as interim until QAPI-based async > >>> monitor support is ready? We could unbreak qxl screendumps without > >>> having to introduce a new (but temporary!) screendump_async command + > >>> completion event. > >> > >> There are a few problems here, but the blocking one is that a command > >> can't go from sync to async. This is an incompatible change. > >> > >> If you mind adding the temporary command and if this issue is so rare > >> that none can reproduce it, then I'd suggest to wait for 1.2. > >> > > > > There are two options really: > > 1. revert the patches that changed qxl screendump to save the ppm > > before (possibly) updating the framebuffer. > > 2. introduce a new command that is really async > > > > The third option, what Gerd proposes, doesn't break the blocking chain > > going from the A, the dual purpose spice client and libvirt client, > > through libvirt, qemu, spice and back to A. > > > > If no one can reproduce the block then it would seem 1 makes sense. > > So let's start with a reproducible test case that demonstrates the problem > before we start introducing new commands then if there's doubt about the > nature > of the problem. Completely agree, I was going to suggest that too.