org.apache.flink.streaming.api.watermark.Watermark Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one
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* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
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*/
package org.apache.flink.streaming.api.watermark;
import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.streaming.runtime.streamrecord.StreamElement;
/**
* A Watermark tells operators that no elements with a timestamp older or equal to the watermark
* timestamp should arrive at the operator. Watermarks are emitted at the sources and propagate
* through the operators of the topology. Operators must themselves emit watermarks to downstream
* operators using {@link org.apache.flink.streaming.api.operators.Output#emitWatermark(Watermark)}.
* Operators that do not internally buffer elements can always forward the watermark that they
* receive. Operators that buffer elements, such as window operators, must forward a watermark after
* emission of elements that is triggered by the arriving watermark.
*
* In some cases a watermark is only a heuristic and operators should be able to deal with late
* elements. They can either discard those or update the result and emit updates/retractions to
* downstream operations.
*
*
When a source closes it will emit a final watermark with timestamp {@code Long.MAX_VALUE}.
* When an operator receives this it will know that no more input will be arriving in the future.
*/
@PublicEvolving
public class Watermark extends StreamElement {
/** The watermark that signifies end-of-event-time. */
public static final Watermark MAX_WATERMARK = new Watermark(Long.MAX_VALUE);
/** The watermark that signifies is used before any actual watermark has been generated. */
public static final Watermark UNINITIALIZED = new Watermark(Long.MIN_VALUE);
// ------------------------------------------------------------------------
/** The timestamp of the watermark in milliseconds. */
protected final long timestamp;
/** Creates a new watermark with the given timestamp in milliseconds. */
public Watermark(long timestamp) {
this.timestamp = timestamp;
}
/** Returns the timestamp associated with this {@link Watermark} in milliseconds. */
public long getTimestamp() {
return timestamp;
}
// ------------------------------------------------------------------------
@Override
public boolean equals(Object o) {
return this == o
|| o != null
&& o.getClass() == this.getClass()
&& ((Watermark) o).timestamp == timestamp;
}
@Override
public int hashCode() {
return (int) (timestamp ^ (timestamp >>> 32));
}
@Override
public String toString() {
return "Watermark @ " + timestamp;
}
}