Reference listeners and null reference lists

[Holly Cummins <cu...@uk.ibm.com>]

Hi all, 

I'm hitting a problem with reference listeners which feels like a mini-bug 
to me, but I thought I'd see what everyone else thinks. I've got a bean 
with a blueprint-injected reference list. The same bean also has a 
reference listener. When the system is initializing, the bind() method is 
called before the reference list has been injected. 

The specification says: "For reference-list callbacks, the service proxy 
is guaranteed to be available in the collection before a bind callback
is invoked, and to remain in the collection until after an unbind callback 
has completed."

The specification doesn't actually say that anyone has to have been told 
about the collection which is being modified, so technically our behaviour 
is within the letter of the spec. However, it feels like the *intention* 
of the specification is that if the bind() method is called consumers of 
the service should have access to a collection which accurately represents 
the final state of the reference list. 

On the other hand, relying on the system being in a particularly 
consistent state during initialisation is obviously unwise, and against 
the more general spirit of OSGi dynamism, so maybe what we're doing is 
perfectly reasonable!

What do people think?

The code I'm using is:

        <bean id="thingAggregator" class="...">
                <property name="things" ref="thinglist" />
        </bean>

        <reference-list
                id="thinglist"
                interface="Thing">
                <reference-listener
                        ref="thingAggregator"
                        bind-method="bind"/>
        </reference-list>


        public void bind(Thing thing) {
                System.out.println("DEBUG: bind called, things is " + 
things);
        }
 

Regards, 
Holly

--
Holly Cummins
IBM Hursley, UK
cumminsh@uk.ibm.com 






Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 
741598. 
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU

Re: Reference listeners and null reference lists

[Mark Nuttall <mn...@apache.org>]

Hi Holly,
This sounds like a bug. I agree that "For reference-list callbacks, the
service proxy is guaranteed to be available in the collection before a bind
callback is invoked" strongly suggests that the new reference should have
been injected before bind() was called.

Regards,
Mark

On 8 May 2011 13:55, Holly Cummins <cu...@uk.ibm.com> wrote:

> Hi all,
>
> I'm hitting a problem with reference listeners which feels like a mini-bug
> to me, but I thought I'd see what everyone else thinks. I've got a bean with
> a blueprint-injected reference list. The same bean also has a reference
> listener. When the system is initializing, the bind() method is called
> before the reference list has been injected.
>
> The specification says: "For reference-list callbacks, the service proxy is
> guaranteed to be available in the collection before a bind callback
> is invoked, and to remain in the collection until after an unbind callback
> has completed."
>
> The specification doesn't actually say that anyone has to have been told
> about the collection which is being modified, so technically our behaviour
> is within the letter of the spec. However, it feels like the *intention* of
> the specification is that if the bind() method is called consumers of the
> service should have access to a collection which accurately represents the
> final state of the reference list.
>
> On the other hand, relying on the system being in a particularly consistent
> state during initialisation is obviously unwise, and against the more
> general spirit of OSGi dynamism, so maybe what we're doing is perfectly
> reasonable!
>
> What do people think?
>
> The code I'm using is:
>
>         <bean id=*"thingAggregator" *class=*"..."*>
>                 <property name=*"things"* ref=*"thinglist"* />
>         </bean>
>
>         <reference-list
>                 id=*"thinglist"*
>                 interface=*"Thing"*>
>                 <reference-listener
>                         ref=*"thingAggregator"*
>                         bind-method=*"bind"*/>
>         </reference-list>
>
>
>         *public* *void* bind(Thing thing) {
>                 System.out.println("DEBUG: bind called, things is " +
> things);
>         }
>
>
> Regards,
> Holly
>
> --
> Holly Cummins
> IBM Hursley, UK
> cumminsh@uk.ibm.com
>
>
>
>  ------------------------------
>
> *
> *
>
> *Unless stated otherwise above:
> IBM United Kingdom Limited - Registered in England and Wales with number
> 741598.
> Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU
> *
>
>
>
>
>
>
>