[jira] Assigned: (DERBY-3405) Examine the possibility of implementing Derby modules as OSGI bundles

["Kathey Marsden (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/DERBY-3405?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Kathey Marsden reassigned DERBY-3405:
-------------------------------------

    Assignee:     (was: Dibyendu Majumdar)

> Examine the possibility of implementing Derby modules as OSGI bundles
> ---------------------------------------------------------------------
>
>                 Key: DERBY-3405
>                 URL: https://issues.apache.org/jira/browse/DERBY-3405
>             Project: Derby
>          Issue Type: New Feature
>          Components: Build tools
>            Reporter: Dibyendu Majumdar
>
> At present, Derby as a whole is offered as an OSGI bundle.
> Internally, Derby does not use OSGI for managing modules. Modules and services (which are collections of modules) are managed using the Monitor component, which is a custom IoC container, designed specifically for Derby.
> Some of the features of the Monitor component, mirror facilities offered by OSGI. The obvious ones are:
> a) Loading modules based upon environment. The features offered by the Monitor subsystem were described by Dan like this:
> The monitor ... selects the module implementation that is suitable for the given environment by:
>   - seeing what the current JDK level is and if a module implementation supports it
>   - seeing what classes a module implementation requires and if they exist
>   - if the module implements ModuleSupportable and if so asking the module if it can support the current environment.
> As an example, modules.properties today contains three JDBC implementations, JSR169, JDBC 3 and JDBC 4, having multiple exist is not an issue, the monitor selects the correct one.
> The ability to load bundles based on environment compatibility is one of OSGI features.
> b) Resolving module interdependencies.
> c) Managing life-cycle of services and modules.
> A migration from the Monitor component to an OSGI based packaging is not going to be an easy transition. At this stage, therefore, this is more of an experiment.
> The benefits of using OSGI are:
> a) It supports dependencies based upon versions of bundles. 
> b) It will make it easier to add/remove components, specially at run-time. However, the use case for this needs defining.
> c) It may open up Derby to other possibilities ... 
> The disadvantages are:
> a) Introduces a dependency on OSGI - whereas Derby at present has its own IoC implementation.
> b) Will mean a major change to how Derby is bundled and therefore potentially impact users.

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