[jira] [Created] (HDFS-14862) Review of MovedBlocks

["David Mollitor (Jira)" <ji...@apache.org>]

David Mollitor created HDFS-14862:
-------------------------------------

             Summary: Review of MovedBlocks
                 Key: HDFS-14862
                 URL: https://issues.apache.org/jira/browse/HDFS-14862
             Project: Hadoop HDFS
          Issue Type: Improvement
          Components: balancer & mover
    Affects Versions: 3.2.0
            Reporter: David Mollitor
            Assignee: David Mollitor
         Attachments: HDFS-14862.1.patch

Internal data structure needs to be protected (synchronized) but is scoped as {{protected}} so any sub-class could modify without a lock.  Synchronize the collection itself for protection.  It also returns the internal data structure in {{getLocations}} so the structure could be modified outside of the lock.  Create a copy instead.

{code:java}
    /** The locations of the replicas of the block. */
    protected final List<L> locations = new ArrayList<L>(3);
    
    public Locations(Block block) {
      this.block = block;
    }
    
    /** clean block locations */
    public synchronized void clearLocations() {
      locations.clear();
    }
...
   /** @return its locations */
    public synchronized List<L> getLocations() {
      return locations;
    }
{code}
 
[https://github.com/apache/hadoop/blob/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/balancer/MovedBlocks.java#L43]

Also, remove a bunch of superfluous and complicated code.



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