[libvirt-users] Designing libvirt client

[Daniel P. Berrange]

On Tue, May 14, 2013 at 05:17:12PM -0700, arvind viswanathan wrote:
> Hi,
> I have a VMM application using a homegrown client for communicating with
> hypervisor.
> I am planning to migrate to libvirt because of the blocking nature of the
> calls.
> After going over the architecture, I would like to have a few doubts
> clarified
> 1) Should my application be necessarily multi-threaded in order to make use
> of the non-blocking calls in libvirt. [Are overlapping methods mainly used
> by multithreaded clients].

The libvirt client & server are both multi-thread safe - you can have
multiple threads using the same virConnectPtr object & it'll do the
right thing with locking. So, yes, our recommendation is to use threads
in applications which need non-blocking behaviour

> 2) I was wondering if there was any way to provide a callback along with
> the methods  to achieve non-blocking.[My application has event library so
> it can receive events]

The only callbacks we have are for receiving event notifications. We
don't have any async methods in the libvirt core API

> 3) Is the libvirt RPC client multi-threaded. [i.e., does it internally use
> multiple threads to dispatch requests to server and return response to the
> application]

Yes, libvirtd is fully multi-threaded and thus will process requests
in parallel, even requests from the same client.


Depending your application, there is also the possibility of using the
slightly higher level   libvirt-gobject library (part of the libvirt-glib
codebase).  This library integrates with GObject and GIO to provide
async methods with callbacks on completion as you describe. The main
limitation of this library is that it doesn't have 100% coverage of the
current main libvirt APIs. It is being developed mostly to serve features
required by the GNOME boxes application, since that's the main user of
it currently. Of course we welcome patches to libvirt-gobject from any
other interested parties. In addition to provide async APIs, it has a
set of objects to managing configuration, so you don't need to use XML
directly.

Daniel
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