samza-api/src/main/java/org/apache/samza/task/TaskCoordinator.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 org.apache.samza.task;

/**
 * TaskCoordinators are provided to the process methods of {@link org.apache.samza.task.StreamTask} implementations
 * to allow the user code to request actions from the Samza framework, including committing the current checkpoints
 * to configured org.apache.samza.checkpoint.CheckpointManager or shutting down the task or all tasks within
 * a container.
 * <p>
 *   This interface may evolve over time.
 * </p>
 */
public interface TaskCoordinator {
  /**
   * Requests that Samza should write out a checkpoint, from which a task can restart
   * after failure.
   *
   * <p>If <code>CURRENT_TASK</code> is given, a checkpoint is only written for the
   * current task. If <code>ALL_TASKS_IN_CONTAINER</code> is given, a checkpoint is
   * written for all tasks in the current container.
   *
   * <p>Note that if you also have also configured your job to commit in regular
   * intervals (using the <code>task.commit.ms</code> property), those time-based
   * commits are not affected by calling this method. Any commits you request explicitly
   * are in addition to timer-based commits. You can set <code>task.commit.ms=-1</code>
   * if you don't want commits to happen automatically.
   *
   * @param scope Which tasks are being asked to commit.
   */
  void commit(RequestScope scope);

  /**
   * Requests that the container should be shut down.
   *
   * <p>If <code>CURRENT_TASK</code> is given, that indicates a willingness of the current
   * task to shut down. All tasks in the container (including the one that requested
   * shutdown) will continue processing messages. Only when every task in the container
   * has called <code>shutdown(CURRENT_TASK)</code>, the container is shut down. Once a
   * task has called <code>shutdown(CURRENT_TASK)</code>, it cannot change its mind
   * (i.e. it cannot revoke its willingness to shut down).
   *
   * <p>If <code>ALL_TASKS_IN_CONTAINER</code> is given, the container will shut down
   * immediately after it has finished processing the current message. Any buffers of
   * pending writes are flushed, but no further messages will be processed in this
   * container.
   *
   * @param scope The approach we should use for shutting down the container.
   */
  void shutdown(RequestScope scope);

  /**
   * A task can make requests to the Samza framework while processing messages, such as
   * {@link TaskCoordinator#commit(RequestScope)} and
   * {@link TaskCoordinator#shutdown(RequestScope)}. This enum is used to indicate
   * whether those requests apply only to the current task, or to all tasks in the
   * current container.
   */
  public enum RequestScope {
    /**
     * Indicates that a request applies only to the task making the call.
     */
    CURRENT_TASK,

    /**
     * Indicates that a request applies to all tasks in the current container.
     */
    ALL_TASKS_IN_CONTAINER;
  }
}