flink BoundedOutOfOrdernessTimestampExtractor

BoundedOutOfOrdernessTimestampExtractor 实现了
AssignerWithPeriodicWatermarks (注册周期生成Watermarks）

源码如下

第一次注册会生成当前最大时间戳currentMaxTimestamp =lastEmittedWatermark + 时间间隔(maxOutOfOrderness)

public abstract class BoundedOutOfOrdernessTimestampExtractor<T> implements AssignerWithPeriodicWatermarks<T> {
      
	private static final long serialVersionUID = 1L;

	/** The current maximum timestamp seen so far. */
	//定义当前最大时间戳
	private long currentMaxTimestamp;

	/** The timestamp of the last emitted watermark. */
	//最后提交的时间戳
	private long lastEmittedWatermark = Long.MIN_VALUE;

	/**
	 * The (fixed) interval between the maximum seen timestamp seen in the records
	 * and that of the watermark to be emitted.
	 */
	private final long maxOutOfOrderness;

	public BoundedOutOfOrdernessTimestampExtractor(Time maxOutOfOrderness) {
		if (maxOutOfOrderness.toMilliseconds() < 0) {
			throw new RuntimeException("Tried to set the maximum allowed " +
				"lateness to " + maxOutOfOrderness + ". This parameter cannot be negative.");
		}
		this.maxOutOfOrderness = maxOutOfOrderness.toMilliseconds();
		this.currentMaxTimestamp = Long.MIN_VALUE + this.maxOutOfOrderness;
	}

	public long getMaxOutOfOrdernessInMillis() {
		return maxOutOfOrderness;
	}

	/**
	 * Extracts the timestamp from the given element.
	 *
	 * @param element The element that the timestamp is extracted from.
	 * @return The new timestamp.
	 */
	public abstract long extractTimestamp(T element);

	@Override
	public final Watermark getCurrentWatermark() {
		// this guarantees that the watermark never goes backwards.
		//这个句代码保证了生成的水印是单调递增的
		//当前最大的时间戳减去延时时间和上次最后提交的水印时间比较
		//保留最大的时间(减去延时时间)作为水印
		long potentialWM = currentMaxTimestamp - maxOutOfOrderness;
		if (potentialWM >= lastEmittedWatermark) {
			lastEmittedWatermark = potentialWM;
		}
		return new Watermark(lastEmittedWatermark);
	}

//提取数据中时间作为timestamp
//如果timestamp 大于最大的currentMaxTimestamp 就把currentMaxTimestamp 置为 timestamp
//返回当前提取到的timestamp
	@Override
	public final long extractTimestamp(T element, long previousElementTimestamp) {
		long timestamp = extractTimestamp(element);
		if (timestamp > currentMaxTimestamp) {
			currentMaxTimestamp = timestamp;
		}
		return timestamp;
	}
}