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https://issues.apache.org/jira/browse/TINKERPOP-2626?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17445401#comment-17445401
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Saikiran Boga commented on TINKERPOP-2626:
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For no.2 "Add a lifecycle state in the steps. Every step should validate that
it is not closed before execution of each result. If it is closed, steps should
throw a IllegalStateException."
I noticed quite a few tests failing when we do this as the tests invoke
something like `hasNext()` after using a full draining terminal method like
toList() on the traversal. This should probably be handled at traversal level
and track if the traversal is closed too.
> RangeGlobalStep closes traversal prematurely
> ---------------------------------------------
>
> Key: TINKERPOP-2626
> URL: https://issues.apache.org/jira/browse/TINKERPOP-2626
> Project: TinkerPop
> Issue Type: Bug
> Components: process
> Affects Versions: 3.4.12, 3.5.1
> Reporter: Divij Vaidya
> Priority: Major
>
> In the RangeGlobalStep.java, this line assumes that RangeGlobalStep will be
> the last step in the traversal. Due to this assumption, it closes the
> traversal when it has no results to share.
> This assumption is not true since a limit() step can be put anywhere in the
> middle of the query e.g. `g.V().limit(2).out()`
> Due to this behaviour, a query such as
> `g.V().limit(2).aggregate('x').cap('x').unfold().out()` will execute the last
> out() step with a "closed traversal". Let's dry run this query:
> The traversal blocks at aggregate barrier step and tries to fetch all
> possible incoming solutions till the aggregate step. limit() will provide 2
> solutions and on the third solution, it will close the traversal and return a
> NoElementFoundException to downstream steps. aggregate() will consider
> NoElementFoundException as a signal for "no more upstream results" and will
> aggregate the two solutions. These two solutions will be forwarded to out()
> step for computation. BUT limit() has already closed the traversal. And
> hence, out() should not be able to execute.
> This inconsistency is not caught in the tests because the tests are run
> against TinkerGraph which will work even if traversal has been closed, hence,
> out() step works even if no underlying iterators are present.
> Solution:
> 1. Remove the line that closes the traversal here:
> [https://github.com/apache/tinkerpop/blame/master/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/filter/RangeGlobalStep.java#L68]
> (along with the incorrect comment)
> 2. Add a lifecycle state in the steps. Every step should validate that it is
> not closed before execution of each result. If it is closed, steps should
> throw a IllegalStateException.
> 3. Enhance TinkerGraph to add a concept of open/closed iterators. Ideally,
> since the iterators were closed on traversal close, out() should not have
> processed successfully in our test cases
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