/**
* 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 java.util.Collection;
import java.util.List;
import org.apache.hadoop.conf.Configurable;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.mapreduce.server.jobtracker.TaskTracker;
/**
* Used by a {@link JobTracker} to schedule {@link Task}s on
* {@link TaskTracker}s.
* <p>
* {@link TaskScheduler}s typically use one or more
* {@link JobInProgressListener}s to receive notifications about jobs.
* <p>
* It is the responsibility of the {@link TaskScheduler}
* to initialize tasks for a job, by calling {@link JobInProgress#initTasks()}
* between the job being added (when
* {@link JobInProgressListener#jobAdded(JobInProgress)} is called)
* and tasks for that job being assigned (by
* {@link #assignTasks(TaskTracker)}).
* @see EagerTaskInitializationListener
*/
abstract class TaskScheduler 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 scheduler to start any work in separate
* threads.
* @throws IOException
*/
public void start() throws IOException {
// do nothing
}
/**
* Lifecycle method to allow the scheduler to stop any work it is doing.
* @throws IOException
*/
public void terminate() throws IOException {
// do nothing
}
/**
* Returns the tasks we'd like the TaskTracker to execute right now.
*
* @param taskTracker The TaskTracker for which we're looking for tasks.
* @return A list of tasks to run on that TaskTracker, possibly empty.
*/
public abstract List<Task> assignTasks(TaskTracker taskTracker)
throws IOException;
/**
* Returns a collection of jobs in an order which is specific to
* the particular scheduler.
* @param queueName
* @return
*/
public abstract Collection<JobInProgress> getJobs(String queueName);
/**
* Abstract QueueRefresher class. Scheduler's can extend this and return an
* instance of this in the {@link #getQueueRefresher()} method. The
* {@link #refreshQueues(List)} method of this instance will be invoked by the
* {@link QueueManager} whenever it gets a request from an administrator to
* refresh its own queue-configuration. This method has a documented contract
* between the {@link QueueManager} and the {@link TaskScheduler}.
*
* Before calling QueueRefresher, the caller must hold the lock to the
* corresponding {@link TaskScheduler} (generally in the {@link JobTracker}).
*/
abstract class QueueRefresher {
/**
* Refresh the queue-configuration in the scheduler. This method has the
* following contract.
* <ol>
* <li>Before this method, {@link QueueManager} does a validation of the new
* queue-configuration. For e.g, currently addition of new queues, or
* removal of queues at any level in the hierarchy is not supported by
* {@link QueueManager} and so are not supported for schedulers too.</li>
* <li>Schedulers will be passed a list of {@link JobQueueInfo}s of the root
* queues i.e. the queues at the top level. All the descendants are properly
* linked from these top-level queues.</li>
* <li>Schedulers should use the scheduler specific queue properties from
* the newRootQueues, validate the properties themselves and apply them
* internally.</li>
* <li>
* Once the method returns successfully from the schedulers, it is assumed
* that the refresh of queue properties is successful throughout and will be
* 'committed' internally to {@link QueueManager} too. It is guaranteed that
* at no point, after successful return from the scheduler, is the queue
* refresh in QueueManager failed. If ever, such abnormalities happen, the
* queue framework will be inconsistent and will need a JT restart.</li>
* <li>If scheduler throws an exception during {@link #refreshQueues()},
* {@link QueueManager} throws away the newly read configuration, retains
* the old (consistent) configuration and informs the request issuer about
* the error appropriately.</li>
* </ol>
*
* @param newRootQueues
*/
abstract void refreshQueues(List<JobQueueInfo> newRootQueues)
throws Throwable;
}
/**
* Get the {@link QueueRefresher} for this scheduler. By default, no
* {@link QueueRefresher} exists for a scheduler and is set to null.
* Schedulers need to return an instance of {@link QueueRefresher} if they
* wish to refresh their queue-configuration when {@link QueueManager}
* refreshes its own queue-configuration via an administrator request.
*
* @return
*/
QueueRefresher getQueueRefresher() {
return null;
}
}