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https://issues.apache.org/jira/browse/UIMA-1153?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12624471#action_12624471
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Marshall Schor commented on UIMA-1153:
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Also check other flow controller examples, and update documentation
> thread safety issue with sample flow controller AdvancedFixedFlowController
> ---------------------------------------------------------------------------
>
> Key: UIMA-1153
> URL: https://issues.apache.org/jira/browse/UIMA-1153
> Project: UIMA
> Issue Type: Bug
> Components: Async Scaleout, Examples
> Affects Versions: 2.2.2
> Reporter: Marshall Schor
> Priority: Minor
>
> The AdvancedFixedFlowController implements its Flow Object class as an inner
> class of its Flow Controller class.
> In UIMA-AS, it is possible that more than one Flow Object can be accessing
> the Flow Controller fields on different threads, and (for Cas Multipliers) it
> is possible for an individual Flow Object to be called on multiple threads at
> the same time (via the method (via the newCasProduced method).
> In the example, the newCasProduced method is marked *synchronized*, so I
> think the same Flow Object will not be running multiple threads at the same
> time, because the other methods to this are all calls done on 1 thread on
> behalf of the main CAS associated with this Flow Object.
> However, multiple flow objects running on different threads could have their
> newCasProduced method called. In this case, the references in that method to
> common mutable fields in the shared Flow Controller object are not
> synchronized. This code should be fixed so that those references are
> synchronized on the same monitor used to synchronize other field access in
> the Flow Controller. UIMA-1149 I hope will use the class instance of the
> flow controller for this purpose, and, assuming that it does, this code
> should explicitly synchronize on that same object, for references to mutable
> fields in that class. There is one field, mSequence, which is in the
> associated Flow Controller class, which is mutable (in theory). References
> to this field should be synchronized with the same monitor used by the flow
> controller class when manipulating it.
> The other field references in the flow object should be checked, and
> synchronized if they refer to mutable Flow Controller fields.
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