[jira] Commented: (LUCENE-942) TopDocCollector.topDocs throws ArrayIndexOutOfBoundsException when called twice

["Hoss Man (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LUCENE-942?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12508018 ] 

Hoss Man commented on LUCENE-942:
---------------------------------

this seems like both a documentation issue, and a bad state checking issue.

the javadoc for topDocs should indicate that it should only be called once all collection is done, and that calling it resets the internal state so that it can no longer be called again.

the internals of topDocs should be changed so that it doesn't rely on "totalHits==0" to indicate if there is a maxScore available and throws a meaninful exception if the method is called more then once.  I would suggest moving the maxScore assignment above the loop using hq.top() as both an indicator of a top score being available and as the top score itself, and wrapping the whole body of the method with something like ...

  if (null == hq) throw new IllegalStateException("topDocs can not be called twice")
  try { 
      ... 
  } finally { hq=null}

> TopDocCollector.topDocs throws ArrayIndexOutOfBoundsException when called twice
> -------------------------------------------------------------------------------
>
>                 Key: LUCENE-942
>                 URL: https://issues.apache.org/jira/browse/LUCENE-942
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: Search
>    Affects Versions: 2.2
>            Reporter: Aaron Isotton
>            Priority: Minor
>
> Here's the implementation of TopDocCollector.topDocs():
>   public TopDocs topDocs() {
>     ScoreDoc[] scoreDocs = new ScoreDoc[hq.size()];
>     for (int i = hq.size()-1; i >= 0; i--)      // put docs in array
>       scoreDocs[i] = (ScoreDoc)hq.pop();
>       
>     float maxScore = (totalHits==0)
>       ? Float.NEGATIVE_INFINITY
>       : scoreDocs[0].score;
>     
>     return new TopDocs(totalHits, scoreDocs, maxScore);
>   }
> When you call topDocs(), hq gets emptied. Thus the second time you call it scoreDocs.length will be 0 and scoreDocs[0] will throw an ArrayIndexOutOfBoundsException.
> I don't know whether this 'call only once' semantics is intended behavior or not; if not, it should be fixed, if yes it should be documented.
> Thanks a lot for an absolutely fantastic product,
> Aaron

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