content: /**
   * 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.activemq.broker.region.policy;
  
  import org.apache.activemq.broker.region.TopicSubscription;
  
  /**
   * A pluggable strategy to calculate the maximum number of messages that are allowed to be pending on 
   * consumers (in addition to their prefetch sizes).
   * 
   * Once the limit is reached, non-durable topics can then start discarding old messages.
   * This allows us to keep dispatching messages to slow consumers while not blocking fast consumers
   * and discarding the messages oldest first.
   *  
   * 
   */
  public interface PendingMessageLimitStrategy {
  
      /**
       * Calculate the maximum number of pending messages (in excess of the prefetch size)
       * for the given subscription
       * 
       * @return the maximum or -1 if there is no maximum
       */
      int getMaximumPendingMessageLimit(TopicSubscription subscription);
  
  }
  