[HDFS-13990] Synchronization Issue With HashResolver

• Type: Bug
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 3.2.0
• Fix Version/s: 3.3.0
• Component/s: federation
• Hadoop Flags: Reviewed
• Assignee: David Mollitor
• Reporter: David Mollitor
• Created: 12/Oct/18 18:10
• Updated: 18/Oct/18 17:30
• Resolved: 18/Oct/18 17:06

Description

HashResolver.java

  private ConsistentHashRing getHashResolver(final Set<String> namespaces) {
    int hash = namespaces.hashCode();
    ConsistentHashRing resolver = this.hashResolverMap.get(hash);
    if (resolver == null) {
      resolver = new ConsistentHashRing(namespaces);
      this.hashResolverMap.put(hash, resolver);
    }
    return resolver;
  }

The hashResolverMap is a ConcurrentHashMap so presumably there is concern here for concurrency issues. However, there is no synchronization around this method, so two threads could call get(hash) both see a 'null' value and then both add two entries into the Map. Add synchronization here.