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From "Richard Eckart de Castilho (Jira)" <...@uima.apache.org>
Subject [jira] [Resolved] (UIMA-4329) Object-based CAS implementation proposal/prototype
Date Tue, 15 Sep 2020 17:28:00 GMT

     [ https://issues.apache.org/jira/browse/UIMA-4329?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Richard Eckart de Castilho resolved UIMA-4329.
    Resolution: Done

[~schor] this work eventually graduated into the new CAS implementation of UIMAv3, right?
Since UIMAv3 is done now, this can be resolved.

> Object-based CAS implementation proposal/prototype
> --------------------------------------------------
>                 Key: UIMA-4329
>                 URL: https://issues.apache.org/jira/browse/UIMA-4329
>             Project: UIMA
>          Issue Type: Brainstorming
>          Components: Core Java Framework
>            Reporter: Nick Hill
>            Priority: Minor
>         Attachments: uima-core_obj-0.5.jar, uima-core_obj-0.5.tar.gz
> I have been experimenting with a simplified CAS implementation where each feature structure
is an object and the indices are based on standard Java SDK concurrent collection classes.
This replaces the complex custom array-based heaps and index implementations.
> The primary motivation was to make the CAS threadsafe so that multiple annotators could
process one concurrently, but I think there are a number of other benefits.
> Summary of advantages:
> - Drastic simplification of code - most proprietary data structure impls removed, many
other classes removed, index/index repo impls are about 25% of the size of the heap versions
(good for future enhancements/maintainability)
> - Thread safety - multiple logically independent annotators can work on the same CAS
concurrently - reading, writing and iterating over feature structures. Opens up a lot of parallelism
> - No need for heap resizing or wasted space in fixed size CAS backing arrays, no large
up-front memory cost for CASes - pooling them should no longer be necessary
> - Unlike the current heap impl, when a FS is removed from CAS indices it's space is actually
freed (can be GC'd)
> - Unification of CAS and JCas - cover class instance (if it exists) "is" the feature
> - Significantly better performance (speed) for many use-cases, especially where there
is heavy access of CAS data
> - Usage of standard Java data structure classes means it can benefit more "for free"
from ongoing improvements in the java SDK and from hardware optimizations targeted at these
> I was hoping to see if there's interest from the community in taking this further, maybe
even as a replacement for the current impl in a future version of uima-core. There has already
been some discussion on the mailing list under the subject "Alternate CAS implementation".
> I'm attaching the current prototype, which should support most existing UIMA functionality
with the exception of:
> - Binary serialization/deserialization
> - C/C++ framework (requires binary serialization)
> - "Delta" CAS related function including CAS markers
> - Index "auto protection" (recent 2.7 feature)
> Note I don't mean to imply these things can't be supported, just that they aren't yet.
> Where these things aren't used it should be possible to try out the attached uima-core.jar
as a drop-in replacement with existing apps/frameworks. An important caveat though is that
any existing JCas cover classes will need recompiling with the new jar (but not re-JCasGenning).
> I'll also attach the code. I started by basically ripping out the CAS heaps, so there's
a lot of code which is just commented out (e.g. in CASImpl.java). Lots of cleanup/tidyup is
still needed, and theres various places which still need fixing for threadsafety (e.g. synchronization
around some existing create-on-first-access logic.. this is separate to the indices though).
But those things shouldn't affect existing usage. A convention I followed was not to rename
modified classes (e.g. CASImpl), but where an equivalent impl was created from scratch I did
give it a new name starting with "CC" (e.g. FeatureStructureImpl is now CCFeatureStructure).
The cc stood for "concurrent CAS". I have kept it in sync with the latest compatible changes
in the uima-core stream, apart from those related to the non-impl'd functions mentioned above.
> Most of the "valid" unit tests work. Some are tied to the internals and no longer apply,
many don't compile because they use binary serialization and/or delta CAS related classes
which I removed for the time being. Some others I had to generalize a bit because for example
they assumed a specific order in places where the order should be arbitrary, and maybe some
other similar reasons.
> md5 checksums:
> {{69f8e01eda8576960a3e6324a0d03d77 *uima-core_obj-0.5.jar}}
> {{3b90ebc78035c68c8c86b31abc8b3b68 *uima-core_obj-0.5.tar.gz}}

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