io.telicent.smart.cache.sources.kafka.policies.automatic.AbstractAutoSeekingPolicy Maven / Gradle / Ivy

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/**
 * Copyright (C) Telicent Ltd
 *
 * Licensed 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 io.telicent.smart.cache.sources.kafka.policies.automatic;

import org.apache.kafka.common.TopicPartition;

import java.util.*;

/**
 * An automatic read policy that seeks within partitions when they are assigned to it guaranteeing that the seek happens
 * only once for each partition
 *
 * @param    Key type
 * @param  Value type
 */
public abstract class AbstractAutoSeekingPolicy extends AbstractAutoReadPolicy {
    private final Set seekedPartitions = new HashSet<>();

    @Override
    protected final void seek(Collection partitions) {
        synchronized (this.seekedPartitions) {
            // Due to consumer group re-balances we could get reassigned the same partitions during the course of our
            // lifetime in which case we do not want to repeatedly seek to the desired position within the topic as that
            // would cause us to redo work everytime a re-balance happens
            List needsSeek = new ArrayList<>();
            for (TopicPartition partition : partitions) {
                if (!seekedPartitions.contains(partition)) {
                    needsSeek.add(partition);
                }
            }
            if (!needsSeek.isEmpty()) {
                seekInternal(needsSeek);
                seekedPartitions.addAll(needsSeek);
            }
        }
    }

    /**
     * Performs the actual seek operation on the given partitions
     *
     * @param partitions Partitions
     */
    protected abstract void seekInternal(Collection partitions);
}