code: public AccumulatorSnapshot getSnapshot() {
  		try {
  			return new AccumulatorSnapshot(jobID, taskID, userAccumulators);
  		} catch (Throwable e) {
  			LOG.warn("Failed to serialize accumulators for task.", e);
  			return null;
  		}
  	}
docs: Creates a snapshot of this accumulator registry.
  @return a serialized accumulator map