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https://issues.apache.org/jira/browse/TINKERPOP-2719?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17508130#comment-17508130
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ASF GitHub Bot commented on TINKERPOP-2719:
-------------------------------------------
FlorianHockmann commented on a change in pull request #1586:
URL: https://github.com/apache/tinkerpop/pull/1586#discussion_r828987815
##########
File path:
gremlin-server/src/main/java/org/apache/tinkerpop/gremlin/server/op/traversal/TraversalOpProcessor.java
##########
@@ -383,9 +383,14 @@ protected void handleIterator(final Context context, final
Iterator itty, final
break;
}
+ // track whether there is anything left in the iterator
because it needs to be accessed after
+ // the transaction could be closed - in that case a call
to hasNext() could open a new transaction
+ // unintentionally
+ final boolean moreInIterator = itty.hasNext();
Review comment:
`hasMore` is only set to `false` in line 401 and that is in the `else`
block of the if condition: `if (moreInIterator)`. So if we also use `hasMore`
here instead, then `hasMore` cannot become `false` any more.
This additional `itty.hasNext()` is needed here to check whether more
elements are available after the last `next()`. This is also explained in the
comment above starting at line 337:
```
// there is a need to check hasNext() on the iterator because if
the channel is not writeable the
// previous pass through the while loop will have next()'d the
iterator and if it is "done" then a
// NoSuchElementException will raise its head. also need a check
to ensure that this iteration doesn't
// require a forced flush which can be forced by sub-classes.
```
This is also in line with the implementation in `AbstractOpProcessor` where
it's implemented exactly like this. We really just copied the logic from there.
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> hasNext is called on TraverserIterator after transaction is committed
> ---------------------------------------------------------------------
>
> Key: TINKERPOP-2719
> URL: https://issues.apache.org/jira/browse/TINKERPOP-2719
> Project: TinkerPop
> Issue Type: Bug
> Components: server
> Affects Versions: 3.5.2
> Reporter: Florian G
> Priority: Major
>
> In {{{}TraversalOpProcessor{}}}, the {{hasNext()}} [function is
> called|https://github.com/apache/tinkerpop/blob/a52887d084053cd420580a0c0a80e745b49ee252/gremlin-server/src/main/java/org/apache/tinkerpop/gremlin/server/op/traversal/TraversalOpProcessor.java#L428]
> on a {{TraversalIterator}} object after the transaction [is
> committed|https://github.com/apache/tinkerpop/blob/a52887d084053cd420580a0c0a80e745b49ee252/gremlin-server/src/main/java/org/apache/tinkerpop/gremlin/server/op/traversal/TraversalOpProcessor.java#L414].
> This causes issues if the database tries to further execute the traversal
> upon the {{hasNext()}} call but has no access to the transaction anymore.
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