code: private boolean shouldProcessTransaction(Action action, long txid) {
          TransactionRequest request = new TransactionRequest(action, txid);
          Integer count;
          if ((count = transactionRequestCount.get(request)) == null) {
              transactionRequestCount.put(request, 1);
              count = 1;
          } else {
              transactionRequestCount.put(request, ++count);
          }
          if (count == checkPointInputTaskCount) {
              transactionRequestCount.remove(request);
              return true;
          }
          return false;
      }
docs: Checks if check points have been received from all tasks across
  all input streams to this component