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The Amazon Kinesis Client Library for Java enables Java developers to easily consume and process data from Amazon Kinesis.

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/*
 *  Copyright 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 *  Licensed under the Amazon Software License (the "License").
 *  You may not use this file except in compliance with the License.
 *  A copy of the License is located at
 *
 *  http://aws.amazon.com/asl/
 *
 *  or in the "license" file accompanying this file. This file 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 software.amazon.kinesis.leases;

import java.util.Collections;
import java.util.List;
import java.util.Map;

import software.amazon.kinesis.leases.exceptions.DependencyException;
import software.amazon.kinesis.leases.exceptions.InvalidStateException;

/**
 * ILeaseTaker is used by LeaseCoordinator to take new leases, or leases that other workers fail to renew. Each
 * LeaseCoordinator instance corresponds to one worker and uses exactly one ILeaseTaker to take leases for that worker.
 */
public interface LeaseTaker {

    /**
     * Compute the set of leases available to be taken and attempt to take them. Lease taking rules are:
     * 
     * 1) If a lease's counter hasn't changed in long enough, try to take it.
     * 2) If we see a lease we've never seen before, take it only if owner == null. If it's owned, odds are the owner is
     * holding it. We can't tell until we see it more than once.
     * 3) For load balancing purposes, you may violate rules 1 and 2 for EXACTLY ONE lease per call of takeLeases().
     * 
     * @return map of shardId to Lease object for leases we just successfully took.
     * 
     * @throws DependencyException on unexpected DynamoDB failures
     * @throws InvalidStateException if lease table does not exist
     */
    Map takeLeases() throws DependencyException, InvalidStateException;

    /**
     * @return workerIdentifier for this LeaseTaker
     */
    String getWorkerIdentifier();

    /**
     * Default implementation returns an empty list and concrete implementaion is expected to return all leases
     * for the application that are in the lease table either by reading lease table or from an internal cache.
     *
     * @return all leases for the application that are in the lease table
     */
    default List allLeases() {
        return Collections.emptyList();
    }
}