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.runtime.impl;
  
  import io.cloudslang.dependency.api.services.DependencyService;
  import org.apache.logging.log4j.LogManager;
  import org.apache.logging.log4j.Logger;
  
  import java.util.Iterator;
  import java.util.LinkedHashMap;
  import java.util.Map;
  import java.util.Set;
  import java.util.concurrent.locks.Lock;
  import java.util.concurrent.locks.ReentrantLock;
  
  /**
   * Created by Genadi Rabinovich, genadi@hpe.com on 05/05/2016.
   */
  public abstract class ExecutionCachedEngine<T extends Executor> extends ExecutionEngine {
      private final Logger logger = LogManager.getLogger(getClass());
      // key --> dependencies concatenated
      // value --> classloader/pythoninterpreter which was build with classpath from these dependencies
      // if we reached the limit of cache we will release the least recently used
      private final Map<String, T> executors = new LinkedHashMap<>();
  
      private final Lock lock = new ReentrantLock();
  
      public T allocateExecutor(Set<String> dependencies) {
          String dependenciesKey = generatedDependenciesKey(dependencies);
  
          T executor;
          T candidateForRemove = null;
          lock.lock();
          try {
              executor = executors.get(dependenciesKey);
              if (executor == null) {
                  int cacheSize = getCacheSize();
                  if (executors.size() == cacheSize) {
                      logger.info("Reached cached executors limit[" + cacheSize + "], replacing LRU executor.");
                      Iterator<Map.Entry<String, T>> iterator = executors.entrySet().iterator();
                      candidateForRemove = iterator.next().getValue();
                      iterator.remove();
                  }
                  executor = createNewExecutor(getDependencyService().getDependencies(dependencies));
              } else {
                  // remove it and place at the end - most recently used
                  executors.remove(dependenciesKey);
              }
              executor.allocate();
              executors.put(dependenciesKey, executor);
          } finally {
              lock.unlock();
          }
          if (candidateForRemove != null) {
              candidateForRemove.close();
          }
          return executor;
      }
  
      protected void releaseExecutor(T executor) {
          executor.release();
      }
  
      protected abstract DependencyService getDependencyService();
  
      protected abstract int getCacheSize();
  
      protected abstract T createNewExecutor(Set<String> filePaths);
  }
  