Chris Nauroth created HDFS-9409:
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             Summary: DataNode shutdown does not guarantee full shutdown of all 
threads due to race condition.
                 Key: HDFS-9409
                 URL: https://issues.apache.org/jira/browse/HDFS-9409
             Project: Hadoop HDFS
          Issue Type: Bug
          Components: datanode
            Reporter: Chris Nauroth


{{DataNode#shutdown}} is documented to return "only after shutdown is 
complete".  Even after completion of this method, it's possible that threads 
started by the DataNode are still running.  Race conditions in the shutdown 
sequence may cause it to skip stopping and joining the {{BPServiceActor}} 
threads.

This is likely not a big problem in normal operations, because these are daemon 
threads that won't block overall process exit.  It is more of a problem for 
tests, because it makes it impossible to write reliable assertions that these 
threads exited cleanly.  For large test suites, it can also cause an 
accumulation of unneeded threads, which might harm test performance.



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