final long getOutputWatermark() {
    if (usedInCurrentTask) {
      // default as input
      return this.outputWatermark;
    } else {
      // always emit the max to indicate no input will be emitted afterwards
      return Long.MAX_VALUE;
    }
  }
Returns the output watermark,
@return output watermark
samza-core/src/main/java/org/apache/samza/operators/impl/OperatorImpl.java