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From Andreas Pieber <anpie...@gmail.com>
Subject Re: Blueprint service reference damping
Date Sat, 06 Aug 2011 10:20:07 GMT
Hey Alasdair,

I've one question belonging to this proposal:

MyService s = injectedReference.get();
if (s != null) {
   s.call();
}

What is supposed to happen if the serviceReference is null?

Thanks and kind regards,
Andreas

On Sat, Aug 6, 2011 at 11:49, Alasdair Nottingham <not@apache.org> wrote:

> Hi,
>
> I've been hitting a few problems with blueprint recently due to the way the
> blueprint service reference damping works. There are two problems that I
> have hit:
>
>   1. When a service goes away and is not replaced, such as on shutdown, if
>   you "accidentally" call a service you get a, by default, 5 minute wait.
>   2. As a user of a service proxy you need to cope with a
>   ServiceUnavailableException. It is especially an issue with optional
> service
>   and if you have a dynamic environment.
>
> The first problem can be overcome by shortening the timeout, but you are
> stuck with the second. I also have the proxy involving less code between me
> and the service. In addition proxying service classes is harder.
>
> For a while now I've been thinking of allowing a mode where you can get a
> raw service injected instead of damped one. The problem is we are only
> supposed to driver the setters once at bean creation, not multiple times.
> After some thought I have an approach which I have proved. The approach is
> that if the target setter takes an AtomicReference we will inject one of
> those and replace the service in the reference behind the scenes. This
> means
> you would write code like:
>
> MyService s = injectedReference.get();
> if (s != null) {
>    s.call();
> }
>
> rather than:
>
> injectedReference.call();
>
> it seems to work quite well. It only affects what is injected, binding
> listeners still have the same behaviour as before. Since this change
> affects
> the programming model somewhat I wanted to see what peoples thoughts were
> before I committed it.
>
> Alasdair
>
> --
> Alasdair Nottingham
> not@apache.org
>

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