Re: [Qemu-devel] [PATCH v3 0/4] Coroutines for better asynchronous programming

[Corentin Chary <corentin.chary@gmail.com>]

On Fri, May 13, 2011 at 11:26 AM, Stefan Hajnoczi
<stefanha@linux.vnet.ibm.com> wrote:
> QEMU is event-driven and suffers when blocking operations are performed because
> VM execution may be stopped until the operation completes.  Therefore many
> operations that could block are performed asynchronously and a callback is
> invoked when the operation has completed.  This allows QEMU to continue
> executing while the operation is pending.
>
> The downside to callbacks is that they split up code into many smaller
> functions, each of which is a single step in a state machine that quickly
> becomes complex and hard to understand.  Callback functions also result in lots
> of noise as variables are packed and unpacked into temporary structs that pass
> state to the callback function.
>
> This patch series introduces coroutines as a solution for writing asynchronous
> code while still having a nice sequential control flow.  The semantics are
> explained in the first patch.  The second patch adds automated tests.
>
> A nice feature of coroutines is that it is relatively easy to take synchronous
> code and lift it into a coroutine to make it asynchronous.  Work has been done
> to move qcow2 request processing into coroutines and thereby make it
> asynchronous (today qcow2 will perform synchronous metadata accesses).  This
> qcow2 work is still ongoing and not quite ready for mainline yet.
>
> Coroutines are also being used for virtfs (virtio-9p) so I have submitted this
> patch now because virtfs patches that depend on coroutines are being published.
>
> Other areas of QEMU that could take advantage of coroutines include the VNC
> server, migration, and qemu-tools.

Hum, the VNC server is already threaded, how would coroutines help  ?
Do you plan to rewrite the server using coroutines instead of threads
?
Thanks
-- 
Corentin Chary
http://xf.iksaif.net