Re: [Qemu-devel] [PATCH v2 1/2] console: add hw_screen_dump_async

[Luiz Capitulino <lcapitulino@redhat.com>]

On Tue, 06 Mar 2012 08:36:34 +0100
Gerd Hoffmann <kraxel@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.