[HDFS-14862] Review of MovedBlocks

• Type: Improvement
• Status: Patch Available
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: 3.2.0
• Component/s: balancer & mover
• Flags: Patch
• Assignee: David Mollitor
• Reporter: David Mollitor
• Created: 20/Sep/19 16:26
• Updated: 25/Sep/19 14:36

Description

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.

    /** 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;
    }

 
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.