Re: [Qemu-devel] [PATCH v6 0/5] Coroutines for better asynchronous programming

[Stefan Hajnoczi <stefanha@gmail.com>]

On Sat, Jul 16, 2011 at 11:08 AM, Blue Swirl <blauwirbel@gmail.com> wrote:
> On Mon, Jun 27, 2011 at 12:21 PM, Stefan Hajnoczi <stefanha@gmail.com> wrote:
>> Here is the latest version of the coroutine series with Mac OS X fixes from
>> Andreas Färber <andreas.faerber@web.de>.
>>
>> 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 second patch.  The fourth 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.
>
> Coroutines seem to work fine on OpenBSD (Sparc64, also tests are
> passed) and mingw32, with a few minor issues.
>
> With simpletrace enabled there is a link failure:
> $ make test-coroutine
>  LINK  test-coroutine
> simpletrace.o: In function `get_clock':
> /src/qemu/qemu-timer.h:117: undefined reference to `use_rt_clock'
>
> This can be fixed for example by adding qemu-timer-common.o to the
> list of linked objects.

Do you want me to send a patch to add qemu-timer-common.o or is this
easy to do while merging?

> I can't compile coroutine tests for Mingw32 because of this:
> $ make test-coroutine
>  CC    test-coroutine.o
> In file included from
> /usr/local/i686-mingw32msvc/include/glib-2.0/glib/galloca.h:30:0,
>                 from /usr/local/i686-mingw32msvc/include/glib-2.0/glib.h:30,
>                 from /src/qemu/test-coroutine.c:14:
> /usr/local/i686-mingw32msvc/include/glib-2.0/glib/gtypes.h:30:24:
> fatal error: glibconfig.h: No such file or directory
>
> I used glib win32 zips from
> http://ftp.gnome.org/pub/gnome/binaries/win32/glib/2.12/, is there a
> better site? Otherwise QEMU builds fine and runs under Wine nicely.

Paolo, Stefan Weil: Any ideas regarding w32 glib headers above?

Stefan