code: void updateNeededReplications(BlockInfo blockInfo,
                                  int curReplicasDelta, 
                                  int expectedReplicasDelta) {
      writeLock();
      try {
        NumberReplicas repl = countNodes(blockInfo);
        int curExpectedReplicas = getReplication(blockInfo);
        neededReplications.update(blockInfo,
          repl.liveReplicas(),
          repl.decommissionedReplicas(),
          curExpectedReplicas,
          curReplicasDelta, expectedReplicasDelta);
      } finally {
        writeUnlock();
      }
    }
docs: /* updates a block in under replication queue