On Tue, Mar 06, 2012 at 09:24:27AM -0300, Luiz Capitulino wrote:
On Tue, 06 Mar 2012 08:36:34 +0100
Gerd Hoffmann<address@hidden> 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.