/*
 * 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.geode.cache;

/**
 * Provides a set of APIs to help the implementation of the <code>CacheLoader</code> load method. An
 * instance of <code>LoaderHelper</code> is only valid within the
 * {@link CacheLoader#load(LoaderHelper) load} method.
 *
 *
 * @see CacheLoader#load(LoaderHelper) load
 * @since GemFire 2.0
 */
public interface LoaderHelper<K, V> {
  /**
   * Searches other caches for the value to be loaded. If the cache is part of a distributed caching
   * system, <code>netSearch</code> will try to locate the requested value in any other cache within
   * the system. If the search is successful, a reference to a local copy of the value is returned.
   * If there is no value for this entry present in the system, and doNetLoad is true, GemFire looks
   * for and invokes <code>CacheLoaders</code> in other nodes in the system. The net load will
   * invoke one loader at a time until a loader either returns a non-null value or throws an
   * exception. If the object is not found, <code>null</code> is returned.
   *
   * @param doNetLoad if true, and there is no valid value found for this entry in the system, then
   *        look for and invoke loaders on other nodes
   *
   * @return the requested value or null if not found
   *
   * @throws TimeoutException if the netSearch times out before getting a response from another
   *         cache
   * @throws CacheLoaderException If <code>netSearch</code> is attempted on a
   *         {@linkplain org.apache.geode.cache.Scope#LOCAL local} region.
   */
  public V netSearch(boolean doNetLoad) throws CacheLoaderException, TimeoutException;

  /**
   * Returns the key for the value being loaded.
   *
   * @return the name Object for the object being loaded
   * @see CacheLoader#load(LoaderHelper) load
   */
  public K getKey();

  /**
   * Returns the region to which the entry belongs.
   *
   * @return the name of the region for the object being loaded
   * @see CacheLoader#load(LoaderHelper) load
   */
  public Region<K, V> getRegion();

  /**
   * Return the argument object for the load method that was passed in from application code. This
   * object is passed in as <i>aLoaderArgument</i> in {@link Region#get(Object, Object) get}.
   * 
   * @return the argument or null if one was not supplied
   */
  public Object getArgument();
}