content: /**
   * 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 org.apache.aurora.scheduler.updater.strategy;
  
  import java.util.Set;
  
  /**
   * A strategy that chooses which instances in a group to update next.
   */
  public interface UpdateStrategy<T> {
  
    /**
     * Gets the next group to update.
     *
     * @param idle Idle instances, candidate for being updated.
     * @param active Instances currently being updated.
     * @return A subset of {@code idle}, instances to start updating.
     */
    Set<T> getNextGroup(Set<T> idle, Set<T> active);
  }
  