content: /* Copyright 2010, Object Management Group, Inc.
   * Copyright 2010, PrismTech, Inc.
   * Copyright 2010, Real-Time Innovations, Inc.
   * All rights reserved.
   *
   * Licensed 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.omg.dds.core.policy;
  
  
  
  /**
   * Controls the criteria used to determine the logical order among changes
   * made by {@link org.omg.dds.pub.Publisher} entities to the same instance of data (i.e.,
   * matching Topic and key). The default kind is
   * {@link DestinationOrder.Kind#BY_RECEPTION_TIMESTAMP}.
   *<p>
   * <b>Concerns:</b> {@link org.omg.dds.topic.Topic}, {@link org.omg.dds.sub.DataReader}, {@link org.omg.dds.pub.DataWriter}
   *<p>
   * <b>RxO:</b> Yes
   *<p>
   * <b>Changeable:</b> No
   *<p>
   * This policy controls how each subscriber resolves the final value of a
   * data instance that is written by multiple DataWriter objects (which may be
   * associated with different Publisher objects) running on different nodes.
   * <p>
   * The setting {@link Kind#BY_RECEPTION_TIMESTAMP} indicates that, assuming
   * the {@link org.omg.dds.core.policy.Ownership} allows it, the latest received value for
   * the instance should be the one whose value is kept. This is the default value.
   * <p>
   * The setting {@link Kind#BY_SOURCE_TIMESTAMP} indicates that, assuming the
   * {@link org.omg.dds.core.policy.Ownership} allows it, a time stamp placed at the source
   * should be used. This is the only setting that, in the case of concurrent
   * same-strength DataWriter objects updating the same instance, ensures all
   * subscribers will end up with the same final value for the instance.
   * This means that the system needs some time synchronization.
   * <p>
   * The value offered is considered compatible with the value requested if and
   * only if the inequality "offered kind &gt;= requested kind" evaluates to
   * true. For the purposes of this inequality, the values of DESTINATION_ORDER
   * kind are considered ordered such that BY_RECEPTION_TIMESTAMP &lt;
   * BY_SOURCE_TIMESTAMP.
   *
   * @see Ownership
   */
  public interface DestinationOrder
  extends QosPolicy.ForTopic,
          QosPolicy.ForDataReader,
          QosPolicy.ForDataWriter,
          RequestedOffered<DestinationOrder>
  {
      // -----------------------------------------------------------------------
      // Methods
      // -----------------------------------------------------------------------
  
      /**
       * @return the kind
       */
      public Kind getKind();
  
  
      // --- Modification: -----------------------------------------------------
  
      /**
       * Copy this policy and override the value of the property.
       * @param kind                   Specifies the order in which the DataReader stores the data.
       *                               This can be BY_RECEPTION_TIMESTAMP or BY_SOURCE_TIMESTAMP.
       *
       * @return  a new DestinationOrder policy
       */
      public DestinationOrder withKind(Kind kind);
  
      /**
       * @return A new DestinationPolicy with reception timestamp ordering.
       */
      public DestinationOrder withReceptionTimestamp();
  
      /**
       * @return A new DestinationPolicy with source timestamp ordering.
       */
      public DestinationOrder withSourceTimestamp();
  
      // -----------------------------------------------------------------------
      // Types
      // -----------------------------------------------------------------------
  
      public enum Kind {
          /**
           * Indicates that data is ordered based on the reception time at each
           * {@link org.omg.dds.sub.Subscriber}. Since each subscriber may receive the data at
           * different times there is no guaranteed that the changes will be
           * seen in the same order. Consequently, it is possible for each
           * subscriber to end up with a different final value for the data.
           */
          BY_RECEPTION_TIMESTAMP,
  
          /**
           * Indicates that data is ordered based on a time stamp placed at the
           * source (by the Service or by the application). In any case this
           * guarantees a consistent final value for the data in all
           * subscribers.
           */
          BY_SOURCE_TIMESTAMP
      }
  
  }
  