void update(EndOfStreamMessage eos, SystemStreamPartition ssp) {
    EndOfStreamState state = eosStates.get(ssp);
    state.update(eos.getTaskName());
  }
Update the state upon receiving an end-of-stream message.
@param eos message of {@link EndOfStreamMessage}
@param ssp system stream partition
samza-core/src/main/java/org/apache/samza/operators/impl/EndOfStreamStates.java