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Re: [Qemu-devel] [PATCH v3 0/4] Coroutines for better asynchronous progr
From: |
Corentin Chary |
Subject: |
Re: [Qemu-devel] [PATCH v3 0/4] Coroutines for better asynchronous programming |
Date: |
Sat, 14 May 2011 08:55:40 +0200 |
On Fri, May 13, 2011 at 11:26 AM, Stefan Hajnoczi
<address@hidden> 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