code: public synchronized void submitOperation(int requestId, AsyncOperation operation) {
          if(this.operations.containsKey(requestId))
              throw new VoldemortException("Request " + requestId
                                           + " already submitted to the system");
  
          this.operations.put(requestId, operation);
          scheduler.scheduleNow(operation);
          logger.debug("Handling async operation " + requestId);
      }
docs: Submit a operations. Throw a run time exception if the operations is
  already submitted
  
  @param operation The asynchronous operations to submit
  @param requestId Id of the request