[libvirt] ruby-libvirt issue

[Chris Lalancette]

On 11/21/10 - 11:25:09PM, Pawel Krzesniak wrote:
> On 29.07.2010 20:32, Chris Lalancette wrote:
> >Ah, OK. So then the question becomes whether the problem is in the ruby
> >bindings not releasing the object in certain circumstances, or in rails
> >holding onto the object too long.  Unfortunately I'm not really that familiar
> >with rails or passenger, so I'm not entirely sure how to figure out where the
> >problem is.
> >
> >I'll see if I can do a bit of testing and look at object lifetimes from the
> >point-of-view of ruby-libvirt to try and eliminate that from the equation.
> 
> following testcase confirms that problem is in bindings itself:

OK, I see what the problem is.  I'm not entirely sure if it is actually a
problem in the bindings, but the behavior is a bit surprising in a
garbage-collected language.  See below.

> ree-1.8.7-2010.02 > require 'libvirt'
>  => true
> ree-1.8.7-2010.02 >   puts `netstat -na|grep -v LISTENING |grep -c
> libvirt-sock`
> 0
>  => nil
> ree-1.8.7-2010.02 > c = Libvirt::open 'qemu:///system'
>  => #<Libvirt::Connect:0x265b718>
> ree-1.8.7-2010.02 > puts `netstat -na|grep -v LISTENING |grep -c
> libvirt-sock`
> 1

After this point, we have a single connection.

>  => nil
> ree-1.8.7-2010.02 > d = c.lookup_domain_by_name 'abc'
>  => #<Libvirt::Domain:0x2705128>
> ree-1.8.7-2010.02 > puts `netstat -na|grep -v LISTENING |grep -c
> libvirt-sock`
> 1

Still the same connection.

>  => nil
> ree-1.8.7-2010.02 > c.close

Here's where the problem is.  Because you are doing c.close before cleaning up
the domain object, the libvirt library keeps a connection open.  If you do
either:

d = nil
GC.start

or

d.free

before the c.close, then everything would be cleaned up correctly.

In terms of making this automatically happen during connection closing, I'm
not entirely sure what we can (and should) do.  I guess we could keep some sort
of list of objects that "depend" on this connection object, and then during
connection close  free them all up.  Does anyone know how the python bindings
handle this?

-- 
Chris Lalancette