/**
 * 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.hadoop.mapred;

import java.io.IOException;

import org.apache.hadoop.conf.Configurable;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.mapreduce.TaskType;

/**
 * A pluggable object that manages the load on each {@link TaskTracker}, telling
 * the {@link TaskScheduler} when it can launch new tasks. 
 */
public abstract class LoadManager implements Configurable {
  protected Configuration conf;
  protected TaskTrackerManager taskTrackerManager;
  
  public Configuration getConf() {
    return conf;
  }

  public void setConf(Configuration conf) {
    this.conf = conf;
  }

  public synchronized void setTaskTrackerManager(
      TaskTrackerManager taskTrackerManager) {
    this.taskTrackerManager = taskTrackerManager;
  }
  
  /**
   * Lifecycle method to allow the LoadManager to start any work in separate
   * threads.
   */
  public void start() throws IOException {
    // do nothing
  }
  
  /**
   * Lifecycle method to allow the LoadManager to stop any work it is doing.
   */
  public void terminate() throws IOException {
    // do nothing
  }
  
  /**
   * Can a given {@link TaskTracker} run another map task?
   * This method should check whether the specified tracker has enough map
   * slots. This method may also check whether the specified tracker has
   * enough resources to run another map task.
   * @param tracker The machine we wish to run a new map on
   * @param totalRunnableMaps Set of running jobs in the cluster
   * @param totalMapSlots The total number of map slots in the cluster
   * @return true if another map can be launched on <code>tracker</code>
   */
  public abstract boolean canAssignMap(TaskTrackerStatus tracker,
      int totalRunnableMaps, int totalMapSlots);

  /**
   * Can a given {@link TaskTracker} run another reduce task?
   * This method should check whether the specified tracker has enough reduce
   * slots.This method may also check whether the specified tracker has
   * enough resources to run another reduce task.
   * @param tracker The machine we wish to run a new map on
   * @param totalRunnableReduces Set of running jobs in the cluster
   * @param totalReduceSlots The total number of reduce slots in the cluster
   * @return true if another reduce can be launched on <code>tracker</code>
   */
  public abstract boolean canAssignReduce(TaskTrackerStatus tracker,
      int totalRunnableReduces, int totalReduceSlots);

  /**
   * Can a given {@link TaskTracker} run another new task from a given job? 
   * This method is provided for use by LoadManagers that take into 
   * account jobs' individual resource needs when placing tasks.
   * @param tracker The machine we wish to run a new map on
   * @param job The job from which we want to run a task on this machine
   * @param type The type of task that we want to run on
   * @return true if this task can be launched on <code>tracker</code>
   */
  public abstract boolean canLaunchTask(TaskTrackerStatus tracker,
      JobInProgress job,  TaskType type);

  /**
   * Obtain the overall number of the slots limit of a tasktracker
   * @param status The status of the tasktracker
   * @param type The type of the task
   * @return The number of maximum slots
   */
  public int getMaxSlots(TaskTrackerStatus status, TaskType type) {
    return (type == TaskType.MAP) ? status.getMaxMapSlots() :
        status.getMaxReduceSlots();
  }

  /**
   * Obtain the number of the slots limit set by setFSMaxSlots
   * @param trackerName The name of the tasktracker
   * @param type The type of the task
   * @return The number of maximum slots set by setFSMaxSlots. Returns
   *          Integer.MAX_VALUE if setFSMaxSlots has not called.
   */
  public int getFSMaxSlots(String trackerName, TaskType type) {
    return Integer.MAX_VALUE;
  }

  /**
   * Set the server-side number of maximum slots on a tasktracker.
   * @param trackerName The name of the tasktracker to set
   * @param type The type of the task to set
   * @param slots New number of maximum slots
   * @throws IOException
   */
  public void setFSMaxSlots(String trackerName, TaskType type, int slots)
      throws IOException {
    throw new IOException(
        "Method setMaxSlots() is not implemented in this LoadManager");
  }
  
  /**
   * Set the number of the maximum slots to the configured number
   * @throws IOException
   */
  public void resetFSMaxSlots() throws IOException {
    throw new IOException(
        "Method clearMaxSlots() is not implemented in this LoadManager");
  }
}