[libvirt] libvirtaio: libvirt-python asyncio event impl

[Daniel P. Berrange]

On Thu, Mar 16, 2017 at 06:24:46PM +0100, Wojtek Porczyk wrote:
> On Thu, Mar 16, 2017 at 04:38:23PM +0000, Daniel P. Berrange wrote:
> > On Thu, Mar 16, 2017 at 05:30:40PM +0100, Wojtek Porczyk wrote:
> > > Hello, libvirt-list,
> > > 
> > > I wrote an event implementation wrapping an asyncio event loop [1].
> > > I would like to contribute it back to libvirt-python, to be offered
> > > alongside the Default Impl in C.
> > > 
> > > [1] https://github.com/woju/libvirtaio
> > > 
> > > Also it contains a workaround for a memory leak around the custom loop
> > > implementation:
> > > https://github.com/woju/libvirtaio/blob/8685cfc/libvirtaio.py#L66-L92
> > > 
> > > How should I submit this? As a patch against libvirt-python.git, appending to
> > > libvirt-override.py?
> > 
> > IIUC, the asyncio module you're using is new in python 3.4 ? The libvirt
> > python code aims to be compatible with python >= 2.6 at this time, so
> > there's a mis-match there.
> >
> > So if we did include that in the main libvirt python module, we'd have
> > to figure out a suitable approach to avoid trying to import the
> > non-existant module when people do "import libvirt".
> 
> That's right, asyncio (and this module) is compatible with 3.3 (mainly because
> of "yield from" syntax) and included in standard library from 3.4. We can ship
> it as separate module (like libvirt vs libvirtmod) and do something like this
> at the beginning on libvirt-override.py:
> 
>     try:
>         from libvirtaio import LibvirtAsyncIOEventImpl  # assuming it won't get renamed in review
>         __all__ += ['LibvirtAsyncIOEventImpl']
>     except (ImportError, SyntaxError):
>         pass
> 
> (Just tested on 2.7).
> 
> People will probably import this unconditionally, since they know, what event
> loop they want to run. In case of doubt, they always can:
> 
>     import libvirt
>     try:
>         libvirt.LibvirtAsyncIOEventImpl().register()
>     except AttributeError:
>         libvirt.virEventRegisterDefaultImpl()
>         def event_loop():
>             while True:
>                 libvirt.virEventRunDefaultImpl()
>                 # ...
>         import threading
>         threading.Thread(target=event_loop).start()
> 
> 
> execute_ff_callback() can be merged regardless, since it is probably
> compatible with 2.5 (that's when ctypes arrived).
> 
> 
> > Or we could just leave it as a standalone python module and document its
> > existence on our python binding page (http://libvirt.org/python.html)
> 
> I'd be glad if you merged this module, since 1) it would be more accessible,
> 2) won't break between releases (currently it is in danger because of the
> opaque object handling). Since we would be (at least now) the only user of
> this, I volunteer as tester/patch submitter against this part of code.

Ok, well just go ahead & submit a suitable patch for libvirt-python and
we'll take the discussion forward from there.


Regards,
Daniel
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