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https://issues.apache.org/jira/browse/HIVE-790?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12748279#action_12748279
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Ning Zhang commented on HIVE-790:
---------------------------------

These functions lacks the CLOSE state check at the beginning:

    if ( state == State.CLOSE )
      return;

So if the close() function is called twice, there is no guard to guarantee the 
body of the close()  (meaning closeOp and close() of all its children) is 
called only once. If we can guarantee the close() is called only once, then 
this implementation should be fine and we don't need two states. 

> race condition related to ScriptOperator + UnionOperator
> --------------------------------------------------------
>
>                 Key: HIVE-790
>                 URL: https://issues.apache.org/jira/browse/HIVE-790
>             Project: Hadoop Hive
>          Issue Type: Bug
>            Reporter: Zheng Shao
>            Assignee: Ning Zhang
>         Attachments: Hive-790.patch, Hive-790_2.patch
>
>
> ScriptOperator uses a second thread to output the rows to the children 
> operators. In a corner case which contains a union, 2 threads might be 
> outputting data into the same operator hierarchy and caused race conditions.
> {code}
> CREATE TABLE tablea (cola STRING);
> SELECT *
> FROM (
>     SELECT TRANSFORM(cola)
>     USING 'cat'
>     AS cola
>     FROM tablea
>   UNION ALL
>     SELECT cola as cola
>     FROM tablea
> ) a;
> {code}

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