Balancer shutdown synchronisation could do with a review
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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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