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https://issues.apache.org/jira/browse/SPARK-44705?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17754394#comment-17754394
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Snoot.io commented on SPARK-44705:
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User 'LuciferYang' has created a pull request for this issue:
https://github.com/apache/spark/pull/42479
> Make PythonRunner single-threaded
> ---------------------------------
>
> Key: SPARK-44705
> URL: https://issues.apache.org/jira/browse/SPARK-44705
> Project: Spark
> Issue Type: Improvement
> Components: PySpark
> Affects Versions: 3.5.0
> Reporter: Utkarsh Agarwal
> Assignee: Utkarsh Agarwal
> Priority: Major
>
> PythonRunner, a utility that executes Python UDFs in Spark, uses two threads
> in a producer-consumer model today. This multi-threading model is problematic
> and confusing as Spark's execution model within a task is commonly understood
> to be single-threaded.
> More importantly, this departure of a double-threaded execution resulted in a
> series of customer issues involving [race
> conditions|https://issues.apache.org/jira/browse/SPARK-33277] and
> [deadlocks|https://issues.apache.org/jira/browse/SPARK-38677] between threads
> as the code was hard to reason about. There have been multiple attempts to
> reign in these issues, viz., [fix
> 1|https://issues.apache.org/jira/browse/SPARK-22535], [fix
> 2|https://github.com/apache/spark/pull/30177], [fix
> 3|https://github.com/apache/spark/commit/243c321db2f02f6b4d926114bd37a6e74c2be185].
> Moreover, the fixes have made the code base somewhat abstruse by introducing
> multiple daemon [monitor
> threads|https://github.com/apache/spark/blob/a3a32912be04d3760cb34eb4b79d6d481bbec502/core/src/main/scala/org/apache/spark/api/python/PythonRunner.scala#L579]
> to detect deadlocks.
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