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From "Jeremiah Lowin (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (AIRFLOW-61) Corner case with deadlocked multiprocessing queues
Date Fri, 06 May 2016 20:46:13 GMT

    [ https://issues.apache.org/jira/browse/AIRFLOW-61?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15274703#comment-15274703
] 

Jeremiah Lowin commented on AIRFLOW-61:
---------------------------------------

+1 and +1 to [~aoen]'s comment above. If Bolke and I hadn't been trying to solve a problem
with the exact same symptom (a stuck DAG), I don't know that I would have realized what was
causing the issue.

> Corner case with deadlocked multiprocessing queues
> --------------------------------------------------
>
>                 Key: AIRFLOW-61
>                 URL: https://issues.apache.org/jira/browse/AIRFLOW-61
>             Project: Apache Airflow
>          Issue Type: Bug
>          Components: scheduler
>    Affects Versions: Airflow 1.7.0
>            Reporter: Jeremiah Lowin
>            Assignee: Jeremiah Lowin
>             Fix For: Airflow 1.7.1
>
>
> I've never experienced this before, but it came up while testing this morning. Joining
a process that puts items in a queue can apparently lead to deadlocks. This happens in the
multiprocessing-enabled scheduler. 
> See for example: https://docs.python.org/3/library/multiprocessing.html#all-start-methods
("Joining processes that use queues") and related issues:
> http://stackoverflow.com/questions/31665328/python-3-multiprocessing-queue-deadlock-when-calling-join-before-the-queue-is-em
> http://stackoverflow.com/questions/31708646/process-join-and-queue-dont-work-with-large-numbers
> http://stackoverflow.com/questions/19071529/python-multiprocessing-125-list-never-finishes



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