code: /*
   * Copyright © 2014-2017 EntIT Software LLC, a Micro Focus company (L.P.)
   *
   * 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.cloudslang.engine.queue.services.assigner.strategies;
  
  import io.cloudslang.engine.queue.services.assigner.ChooseWorkerStrategy;
  
  import java.util.concurrent.ConcurrentMap;
  
  import static com.google.common.cache.CacheBuilder.newBuilder;
  import static io.cloudslang.engine.queue.enums.AssignStrategy.RANDOM;
  import static io.cloudslang.engine.queue.enums.AssignStrategy.ROUND_ROBIN;
  import static io.cloudslang.engine.queue.enums.AssignStrategy.getAssignedStrategy;
  import static io.cloudslang.engine.queue.services.assigner.ExecutionAssignerServiceImpl.WORKER_MESSAGE_ASSIGNMENT_POLICY_KEY;
  import static java.lang.Integer.getInteger;
  import static java.util.concurrent.TimeUnit.HOURS;
  
  public class RoundRobinStrategy implements ChooseWorkerStrategy {
  
      private static final int SEVEN_DAYS_IN_HOURS = 7 * 24;
      private static final int CACHE_MAX_ENTRIES = getInteger("worker.roundRobin.activeGroupAlias.maxSize", 10_000);
      private static final int MAX_CONCURRENCY_LEVEL = getInteger("worker.roundRobin.concurrencyLevel", 16);
      private static final int EXPIRE_NUMBER_OF_HOURS = getInteger("worker.roundRobin.expireAfterAccess", SEVEN_DAYS_IN_HOURS);
  
      private static final ConcurrentMap<String, Integer> groupAliasLatestWorkerMap = newBuilder()
              .maximumSize(isStrategyInUse() ? CACHE_MAX_ENTRIES : 0)
              .concurrencyLevel(MAX_CONCURRENCY_LEVEL)
              .expireAfterAccess(EXPIRE_NUMBER_OF_HOURS, HOURS)
              .<String, Integer>build().asMap();
  
      @Override
      public int getNextWorkerFromGroup(String groupAlias, int numberOfWorkersInGroup) {
          return groupAliasLatestWorkerMap.merge(groupAlias, 0,
                  (oldValue, newValue) -> {
                      int nextOldValue = oldValue + 1;
                      return nextOldValue < numberOfWorkersInGroup ? nextOldValue : 0;
                  });
      }
  
      private static boolean isStrategyInUse() {
          return getAssignedStrategy(System.getProperty(WORKER_MESSAGE_ASSIGNMENT_POLICY_KEY), RANDOM) == ROUND_ROBIN;
      }
  
  }
  