/*
* 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.functions;
import org.apache.flink.api.common.functions.Function;
/**
* A {@code TimestampAssigner} assigns event time timestamps to elements.
* These timestamps are used by all functions that operate on event time,
* for example event time windows.
*
* <p>Timestamps are represented in milliseconds since the Epoch
* (midnight, January 1, 1970 UTC).
*
* @param <T> The type of the elements to which this assigner assigns timestamps.
*/
public interface TimestampAssigner<T> extends Function {
/**
* Assigns a timestamp to an element, in milliseconds since the Epoch.
*
* <p>The method is passed the previously assigned timestamp of the element.
* That previous timestamp may have been assigned from a previous assigner,
* by ingestion time. If the element did not carry a timestamp before, this value is
* {@code Long.MIN_VALUE}.
*
* @param element The element that the timestamp is wil be assigned to.
* @param previousElementTimestamp The previous internal timestamp of the element,
* or a negative value, if no timestamp has been assigned, yet.
* @return The new timestamp.
*/
long extractTimestamp(T element, long previousElementTimestamp);
}