org.apache.flink.streaming.api.watermark.Watermark Maven / Gradle / Ivy
/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* 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,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.flink.streaming.api.watermark;
import org.apache.flink.streaming.runtime.streamrecord.StreamElement;
/**
* A Watermark tells operators that receive it 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.
*
*/
public class Watermark extends StreamElement {
/** The timestamp of the watermark */
private final long timestamp;
/**
* Creates a new watermark with the given timestamp.
*/
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() == Watermark.class && ((Watermark) o).timestamp == this.timestamp;
}
@Override
public int hashCode() {
return (int) (timestamp ^ (timestamp >>> 32));
}
@Override
public String toString() {
return "Watermark @ " + timestamp;
}
}