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https://issues.apache.org/jira/browse/UIMA-4146?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14241084#comment-14241084
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Marshall Schor commented on UIMA-4146:
--------------------------------------
Thanks for expanding on this :-). I've been too bogged down in getting the new
stuff to work (and along the way learning the details of the indexing /
iterating / deserializing code) to focus more broadly....
The snapshot stuff I want to work for both non-JCas and JCas approaches.
Because UIMA Core already has support for the extended-for for FSIndex impl,,
I'm just piggy-backing on top of that. If you want "snapshot" style, you would:
{code:java}
// instead of
for (AnnotationFS : cas.getAnnotationIndex(type)) { ... }
// you would write
for (AnnotationFS : cas.getAnnotationIndex(type).withSnapshotIterators()) { ...
}
{code}
I think the difference vs the "select" approach might be that select
materializes (as actual Java Objects) all the FSs before the iteration starts,
while the snapshot stuff doesn't - it is just "copying" the index (as a set of
IntVectors), although it is converting the "Set" form to a "Sorted" form
internally (which is more efficient and ok because this special index is
read-only).
I haven't considered approaches to make things more capable for Generics,
although I've seen some examples. That sounds like a good extension - maybe
for the next release after this one... I think that (at least for me) this
might take some "quality thought time" which I'm short of right now :-)
> Support Snapshot iterators for FSIndexes
> ----------------------------------------
>
> Key: UIMA-4146
> URL: https://issues.apache.org/jira/browse/UIMA-4146
> Project: UIMA
> Issue Type: New Feature
> Components: Core Java Framework
> Reporter: Marshall Schor
> Assignee: Marshall Schor
> Fix For: 2.7.0SDK
>
>
> Implementing "protectIndices" could have a consequence that some updated FSs
> could be removed from the indices by the framework, and addedback later. If
> the user code were iterating they might get unexpected
> ConcurrentModificationExceptions because of this.
> Extend the iterators to include "snapshot" iterators, that take a snapshot of
> the index contents at iterator creation time, and then use that to iterate
> over; this allows the iterator to avoid ConcurrentModificationExceptions.
> Do this in a manner to continue to support the "extended for" style of
> iterating, where you can write
> {code:java}
> for (MyAnnotation : fsIndexProducingSnapshotIterators) { ... }
> {code}
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