[jira] [Commented] (SPARK-3384) Potential thread unsafe Breeze vector addition in KMeans

["Xiangrui Meng (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-3384?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14120285#comment-14120285 ] 

Xiangrui Meng commented on SPARK-3384:
--------------------------------------

[~rnowling] Could you provide a code example that can re-produce the bug you observed in local testing? Breeze's += is not thread-safe. But in a Spark job, calls to a resultHandler is synchronized: https://github.com/apache/spark/blob/master/core/src/main/scala/org/apache/spark/scheduler/JobWaiter.scala#L52 .

> Potential thread unsafe Breeze vector addition in KMeans
> --------------------------------------------------------
>
>                 Key: SPARK-3384
>                 URL: https://issues.apache.org/jira/browse/SPARK-3384
>             Project: Spark
>          Issue Type: Bug
>          Components: MLlib
>            Reporter: RJ Nowling
>
> In the KMeans clustering implementation, the Breeze vectors are accumulated using +=.  For example,
> https://github.com/apache/spark/blob/master/mllib/src/main/scala/org/apache/spark/mllib/clustering/KMeans.scala#L162
>  This is potentially a thread unsafe operation.  (This is what I observed in local testing.)  I suggest changing the += to + -- a new object will be allocated but it will be thread safe since it won't write to an old location accessed by multiple threads.
> Further testing is required to reproduce and verify.



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