distributedlog-service/src/main/java/com/twitter/distributedlog/service/placement/PlacementStateManager.java

/**
 * 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 com.twitter.distributedlog.service.placement;

import java.util.TreeSet;

/**
 * The PlacementStateManager handles persistence of calculated resource placements including, the
 * storage once the calculated, and the retrieval by the other shards.
 */
public interface PlacementStateManager {

  /**
   * Saves the ownership mapping as a TreeSet of ServerLoads to persistent storage
   */
  void saveOwnership(TreeSet<ServerLoad> serverLoads) throws StateManagerSaveException;

  /**
   * Loads the ownership mapping as TreeSet of ServerLoads from persistent storage
   */
  TreeSet<ServerLoad> loadOwnership() throws StateManagerLoadException;

  /**
   * Watch the persistent storage for changes to the ownership mapping and calls placementCallback
   * with the new mapping when a change occurs
   */
  void watch(PlacementCallback placementCallback);

  interface PlacementCallback {
    void callback(TreeSet<ServerLoad> serverLoads);
  }

  abstract class StateManagerException extends Exception {
    public StateManagerException(String message, Exception e) {
      super(message, e);
    }
  }

  class StateManagerLoadException extends StateManagerException {
    public StateManagerLoadException(Exception e) {
      super("Load of Ownership failed", e);
    }
  }

  class StateManagerSaveException extends StateManagerException {
    public StateManagerSaveException(Exception e) {
      super("Save of Ownership failed", e);
    }
  }
}