code: public boolean pin(@NonNull VoidAggregation aggregation) {
          RequestDescriptor descriptor =
                          RequestDescriptor.createDescriptor(aggregation.getOriginatorId(), aggregation.getTaskId());
          VoidAggregation existing = clipboard.get(descriptor);
          if (existing == null) {
              existing = aggregation;
              trackingCounter.incrementAndGet();
              clipboard.put(descriptor, aggregation);
          }
  
          existing.accumulateAggregation(aggregation);
  
          //if (counter.incrementAndGet() % 10000 == 0)
          //    log.info("Clipboard stats: Totals: {}; Completed: {};", clipboard.size(), completedQueue.size());
  
          int missing = existing.getMissingChunks();
          if (missing == 0) {
              //  completedQueue.add(existing);
              completedCounter.incrementAndGet();
              return true;
          } else
              return false;
      }
docs: This method places incoming VoidAggregation into clipboard, for further tracking
  
  @param aggregation
  @return TRUE, if given VoidAggregation was the last chunk, FALSE otherwise