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From "Steve Loughran (JIRA)" <j...@apache.org>
Subject [jira] Created: (HDFS-852) Balancer shutdown synchronisation could do with a review
Date Thu, 24 Dec 2009 12:00:30 GMT
Balancer shutdown synchronisation could do with a review

                 Key: HDFS-852
                 URL: https://issues.apache.org/jira/browse/HDFS-852
             Project: Hadoop HDFS
          Issue Type: Improvement
          Components: balancer
    Affects Versions: 0.22.0
            Reporter: Steve Loughran
            Priority: Minor

Looking at the source of the Balancer, there's a lot {{catch(InterruptedException)}} clauses,
which runs the risk of swallowing exceptions, making it harder to shut down a balancer.

for example, the {{AccessKeyUpdater swallows the InterruptedExceptions which get used to tell
it to shut down, and while it does poll the shared field {{shouldRun}}, that field isn't volatile:
the shutdown may }}not work. 

Elsewhere, the {{dispatchBlocks()}} method swallows interruptions without even looking for
any shutdown flag. 

This is all minor as it is shutdown logic, but it is the stuff that it hard to test and leads
to problems in the field, the problems that leave the ops team resorting to {{kill -9}}, and
we don't want that.

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