content: /*
   * 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.assignment;
  
  import org.apache.kafka.streams.processor.TaskId;
  import org.apache.kafka.streams.processor.assignment.AssignmentConfigs;
  import org.apache.kafka.streams.processor.assignment.ProcessId;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.util.Map;
  import java.util.Set;
  
  import static org.apache.kafka.streams.processor.internals.assignment.StandbyTaskAssignmentUtils.computeTasksToRemainingStandbys;
  import static org.apache.kafka.streams.processor.internals.assignment.StandbyTaskAssignmentUtils.createLeastLoadedPrioritySetConstrainedByAssignedTask;
  import static org.apache.kafka.streams.processor.internals.assignment.StandbyTaskAssignmentUtils.pollClientAndMaybeAssignAndUpdateRemainingStandbyTasks;
  
  /**
   * Default standby task assignor that distributes standby tasks to the least loaded clients.
   *
   * @see ClientTagAwareStandbyTaskAssignor
   */
  class DefaultStandbyTaskAssignor implements StandbyTaskAssignor {
      private static final Logger log = LoggerFactory.getLogger(DefaultStandbyTaskAssignor.class);
  
      @Override
      public boolean assign(final Map<ProcessId, ClientState> clients,
                            final Set<TaskId> allTaskIds,
                            final Set<TaskId> statefulTaskIds,
                            final AssignmentConfigs configs) {
          final int numStandbyReplicas = configs.numStandbyReplicas();
          final Map<TaskId, Integer> tasksToRemainingStandbys = computeTasksToRemainingStandbys(numStandbyReplicas,
                                                                                                statefulTaskIds);
  
          final ConstrainedPrioritySet standbyTaskClientsByTaskLoad = createLeastLoadedPrioritySetConstrainedByAssignedTask(clients);
  
          standbyTaskClientsByTaskLoad.offerAll(clients.keySet());
  
          for (final TaskId task : statefulTaskIds) {
              pollClientAndMaybeAssignAndUpdateRemainingStandbyTasks(numStandbyReplicas,
                                                                     clients,
                                                                     tasksToRemainingStandbys,
                                                                     standbyTaskClientsByTaskLoad,
                                                                     task,
                                                                     log);
          }
  
          // returning false, because standby task assignment will never require a follow-up probing rebalance.
          return false;
      }
  }
  