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https://issues.apache.org/jira/browse/FELIX-2994?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Pierre De Rop updated FELIX-2994:
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Attachment: FELIX-2994.tgz
attached the proposed implementation for delayed components.
> Delayed Components in Dependency Manager
> ----------------------------------------
>
> Key: FELIX-2994
> URL: https://issues.apache.org/jira/browse/FELIX-2994
> Project: Felix
> Issue Type: Improvement
> Components: Dependency Manager
> Reporter: Pierre De Rop
> Priority: Minor
> Attachments: FELIX-2994.tgz
>
>
> This issue proposes a lightweight implementation for the support of "delayed
> components" in Dependency Manager.
> (see patch attached to this issue).
> It allows components to delay their possibly expensive activation until they
> are really used, and allows
> Dependency Manager to instantiate/initialize components only as needed.
> For system where many services are installed, and where not every services
> are actually used, then this feature
> can significantly speed up startup time, especially when some unused
> components require an expensive
> processing from their "init" / "start" methods.
> A new "setDelayed(boolean)" method has been added in the Component interface,
> and also a new "delayed" state
> has been added in the ComponentDeclaration, allowing to browse delayed
> components from the DM shell.
> Here is a code example which defines a delayed component:
> dm.add(createComponent()
> .setImplementation(DelayedServiceImpl.class)
> .setInterface(DelayedService.class.getName, null)
> .setDelayed(true));
> Implementation notes
> --------------------------
> - By default, components are not delayed (as before).
> - A new DelayedComponentTest has been added in the test sub-project
>
> - This implementation is simple and is not intrusive: DM core classes
> *have not* been modified
> (excepts a micro-modif in ComponentImpl.java, and in
> ComponentDeclaration.java). Basically,
> we track every service listeners, and when a listener is matching a
> delayed component, then
> the component is started. Else, the component is not started, hence
> avoiding the useless component
> instantiation/initialization.
> - A new state has been added in the ComponentDeclaration class
> (STATE_DELAYED), allowing to track
> delayed components from the Dependency Manager shell.
> - The new filter index recently introduced in DM has not yet been used,
> but it might be useful to
> integrate it in the delayed component manager, since the DM indexer
> greatly speeds up service listeners lookup,
> especially when using many (thousands) of services. But this enhancement
> could be done in a next step.
> - The ListenerHook (from ServiceHook specification) is used for the
> implementation: this allows to trigger the
> activation of DM delayed components not only using DependencyManager
> dependencies, but also using other libraries,
> like Declarative Service, iPOJO, blueprint, or even ServiceTracker.
> This is important because
> in our environment, we are using both dependency manager and Declarative
> Service, and we need to be able to
> activate a delayed DM component from a Declarative Service "Reference"
> dependency. ListenerHook
> allows to do this because using ListenerHook, we are able to track every
> service listeners registered in the framework.
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