streams/src/main/java/org/apache/kafka/streams/processor/internals/MinTimestampTracker.java

/**
 * 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.kafka.streams.processor.internals;

import java.util.LinkedList;

/**
 * MinTimestampTracker implements {@link TimestampTracker} that maintains the min
 * timestamp of the maintained stamped elements.
 */
public class MinTimestampTracker<E> implements TimestampTracker<E> {

    private final LinkedList<Stamped<E>> descendingSubsequence = new LinkedList<>();

    // in the case that incoming traffic is very small, the records maybe put and polled
    // within a single iteration, in this case we need to remember the last polled
    // record's timestamp
    private long lastKnownTime = NOT_KNOWN;

    /**
     * @throws NullPointerException if the element is null
     */
    public void addElement(Stamped<E> elem) {
        if (elem == null) throw new NullPointerException();

        Stamped<E> minElem = descendingSubsequence.peekLast();
        while (minElem != null && minElem.timestamp >= elem.timestamp) {
            descendingSubsequence.removeLast();
            minElem = descendingSubsequence.peekLast();
        }
        descendingSubsequence.offerLast(elem);
    }

    public void removeElement(Stamped<E> elem) {
        if (elem != null && descendingSubsequence.peekFirst() == elem)
            descendingSubsequence.removeFirst();

        if (descendingSubsequence.isEmpty())
            lastKnownTime = elem.timestamp;
    }

    public int size() {
        return descendingSubsequence.size();
    }

    public long get() {
        Stamped<E> stamped = descendingSubsequence.peekFirst();

        if (stamped == null)
            return lastKnownTime;
        else
            return stamped.timestamp;
    }

}