1 WaterMark生成工作机制

 观察源码

/*** A WatermarkGenerator for situations where records are out of order, but you can place an upper* bound on how far the events are out of order. An out-of-order bound B means that once an event* with timestamp T was encountered, no events older than {@code T - B} will follow any more.** 
The watermarks are generated periodically. The delay introduced by this watermark strategy is* the periodic interval length, plus the out-of-orderness bound.*/
@Public
public class BoundedOutOfOrdernessWatermarks implements WatermarkGenerator {/** The maximum timestamp encountered so far. */private long maxTimestamp;/** The maximum out-of-orderness that this watermark generator assumes. */private final long outOfOrdernessMillis;/*** Creates a new watermark generator with the given out-of-orderness bound.** @param maxOutOfOrderness The bound for the out-of-orderness of the event timestamps.*/public BoundedOutOfOrdernessWatermarks(Duration maxOutOfOrderness) {checkNotNull(maxOutOfOrderness, "maxOutOfOrderness");checkArgument(!maxOutOfOrderness.isNegative(), "maxOutOfOrderness cannot be negative");this.outOfOrdernessMillis = maxOutOfOrderness.toMillis();// start so that our lowest watermark would be Long.MIN_VALUE. this.maxTimestamp = Long.MIN_VALUE + outOfOrdernessMillis + 1;}// ------------------------------------------------------------------------@Overridepublic void onEvent(T event, long eventTimestamp, WatermarkOutput output) {maxTimestamp = Math.max(maxTimestamp, eventTimestamp);}@Overridepublic void onPeriodicEmit(WatermarkOutput output) {output.emitWatermark(new Watermark(maxTimestamp - outOfOrdernessMillis - 1));}
}