/
WatermarkGenerator.java
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/
WatermarkGenerator.java
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/*
* 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.api.common.eventtime;
import org.apache.flink.annotation.Public;
import org.apache.flink.api.common.ExecutionConfig;
/**
* The {@code WatermarkGenerator} generates watermarks either based on events or periodically (in a
* fixed interval).
*
* <p><b>Note:</b> This WatermarkGenerator subsumes the previous distinction between the {@code
* AssignerWithPunctuatedWatermarks} and the {@code AssignerWithPeriodicWatermarks}.
*/
@Public
public interface WatermarkGenerator<T> {
/**
* Called for every event, allows the watermark generator to examine and remember the event
* timestamps, or to emit a watermark based on the event itself.
*/
void onEvent(T event, long eventTimestamp, WatermarkOutput output);
/**
* Called periodically, and might emit a new watermark, or not.
*
* <p>The interval in which this method is called and Watermarks are generated depends on {@link
* ExecutionConfig#getAutoWatermarkInterval()}.
*/
void onPeriodicEmit(WatermarkOutput output);
}