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https://issues.apache.org/jira/browse/NIFI-2979?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16218899#comment-16218899
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ASF subversion and git services commented on NIFI-2979:
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Commit 10f27cd5f0c077ad99848453ecaa253ca8ee5f9a in nifi's branch
refs/heads/master from [~jmark99]
[ https://git-wip-us.apache.org/repos/asf?p=nifi.git;h=10f27cd ]
NIFI-2979 PriorityAttributePrioritizer violates Comparator contract. This
closes #2220.
Modified the return value when both objects priority values are null to
zero to match the expected return value based upon the Comparator
contract.
> PriorityAttributePrioritizer violates Comparator contract
> ---------------------------------------------------------
>
> Key: NIFI-2979
> URL: https://issues.apache.org/jira/browse/NIFI-2979
> Project: Apache NiFi
> Issue Type: Bug
> Reporter: Brandon DeVries
> Assignee: Mark Owens
>
> The documentation for the compare() method of the Comparator interface\[1]
> states:
> {quote}
> The implementor must ensure that sgn(compare(x, y)) == -sgn(compare(y, x))
> for all x and y.
> {quote}
> However, in the PriorityAttributePrioritizer\[2], we have the following
> snippet:
> {code}
> String o1Priority = o1.getAttribute(CoreAttributes.PRIORITY.key());
> String o2Priority = o2.getAttribute(CoreAttributes.PRIORITY.key());
> if (o1Priority == null && o2Priority == null) {
> return -1; // this is not 0 to match FirstInFirstOut
> } else if (o2Priority == null) {
> return -1;
> } else if (o1Priority == null) {
> return 1;
> }
> {code}
> This implies that for two non-null FlowFiles f1 and f2, both with null
> "priority" attributes, we would have:
> {code}
> compare(f1, f2) == -1
> compare(f2, f1) == -1
> {code}
> This would appear to violate the contract of the Comparator interface. The
> comment suggests this was done to preserve FIFO ordering, however a return of
> 0 should do the same, and satisfy the contract.
> \[1]
> https://docs.oracle.com/javase/7/docs/api/java/util/Comparator.html#compare%28T,%20T%29
> \[2]
> https://github.com/apache/nifi/blob/d838f61291d2582592754a37314911b701c6891b/nifi-nar-bundles/nifi-standard-bundle/nifi-standard-prioritizers/src/main/java/org/apache/nifi/prioritizer/PriorityAttributePrioritizer.java#L49-L57
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