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From Carsten Ziegeler <cziege...@apache.org>
Subject Re: Problems with lazy loading components
Date Mon, 17 Oct 2005 08:36:14 GMT
Daniel Fagerstrom wrote:
> While working on the block architecture yesterday, I saw that most of 
> the test cases 
> (org.apache.cocoon.test.components.blocks.BlocksManagerTestCase) failed. 
> The problem was that block local files where resolved in wrong context. 
> After having controlled that nothing in the source resolution mechanism 
> had changed since last time I run the tests, I started to suspect the 
> lazy loading of components. After having switch to eager loading 
> everything worked again.
> 
> What happens is the following: The CocoonSourceResolver resolves 
> relative the current processor (via 
> EnvironmentHelper.getCurrentProcessor()) if there is a current processor 
> and otherwise relative the context root from the Avalon context. So, 
> during eager loading of global components there is not yet a current 
> processor, so the source reolution within the components will be 
> relative the root context of the component manager of the component. 
> This is the correct behaviour.
> 
> During lazy loading the source resolution in the component will be 
> relative the context of the processor that it happen to be first used 
> in. This is in general wrong and can be rather confusing and complicated 
> to find what went wrong.
> 
> I think the main problem is that we have a global source resolver and 
> try to get the context right during resolution in a smart and subtle 
> (and fragile) way. If we instead create one source reolver within each 
> service manager all source resolution within a specific service manager 
> will be relative to the context of the service manager irrespectible of 
> when the resolution is done, whether it is eager or lazy. It will also 
> simplify the architecture, and maybe we could get rid of the source 
> resolver from the Processor interface.
> 
> Anyway, I suggest that we turn of lazy loading until we have solved this 
> issue.
> 
> WDYT?
> 
As posted last week, we had several problems with lazy loading as well.
It requires a very careful configuration of your components and if
something goes wrong, it's rather complicated to find out what is going
on/wrong.
I'm actually not sure what lazy loading really gives us? Ok, Cocoon
starts faster, but if you have just configured the blocks you need I
think there is not really a difference. And if you need the components
anyway, you have to wait for them to be setup - being it lazy or not.

Currently, each sitemap has an own source resolver which is the
EnvironmentHelper, so it shouldn't be that hard to add this to the
service manager. But I'm not sure if this helps in all cases as
currently sources are resolved relative to the sitemap they are used in
and not relative to the sitemap they are defined in.

Carsten
-- 
Carsten Ziegeler - Open Source Group, S&N AG
http://www.s-und-n.de
http://www.osoco.org/weblogs/rael/

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