code: void add(BlockInfo block, int numReplicas) {
      synchronized (pendingReplications) {
        PendingBlockInfo found = pendingReplications.get(block);
        if (found == null) {
          pendingReplications.put(block, new PendingBlockInfo(numReplicas));
        } else {
          found.incrementReplicas(numReplicas);
          found.setTimeStamp();
        }
      }
    }
docs: Add a block to the list of pending Replications