[jira] Work started: (UIMA-386) Switching to use correct class loader

["Marshall Schor (JIRA)" <ui...@incubator.apache.org>]

     [ https://issues.apache.org/jira/browse/UIMA-386?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Work on UIMA-386 started by Marshall Schor.

> Switching to use correct class loader
> -------------------------------------
>
>                 Key: UIMA-386
>                 URL: https://issues.apache.org/jira/browse/UIMA-386
>             Project: UIMA
>          Issue Type: Improvement
>          Components: Core Java Framework
>    Affects Versions: 2.1
>            Reporter: Marshall Schor
>         Assigned To: Marshall Schor
>             Fix For: 2.2
>
>
> The current design presumes one classloader is used for all components in an application.  This shows up in the implementation when using JCas - the class loader used to load the JCas cover classes is set up in the CAS, and there is only one there.  This works, unless the analysis engine component is loaded by a different class loader.  This causes strange class-cast exceptions, where the source and target classes look to be identical (what's happening is that the classes are named the same, including having the same package names, but are loaded with different class loaders).  A fix is needed that insures the class loader used for JCas can be switched when an analysis engine component is run.  This should be time-efficient because the flow controller could be under a different class loader than the delegates it's controlling, so the class loader could be switching back and forth twice per delegate dispatch.
> A proposed approach is to add an internal method to the CAS, useClassLoader(xxx), which will be called by the framework just before the processCas call, passing in the class loader that was used to load the analysis engine class.  The framework will check to see if this is the current in-use class loader, and if it is, do nothing.  If it isn't, if the JCas is instantiated, it will call a new JCas method, switchClassLoader(xxx). This method will (a) reset the cache JCas uses to reduce object creation for JCas objects, and do what's needed to load or switch to the right set of iterator generators.  Where possible, re-loading will be avoided, to make the switch fast.

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