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Java > Open Source Codes > org > apache > activemq > broker > region > policy > PendingMessageLimitStrategy


1 /**
2  *
3  * Licensed to the Apache Software Foundation (ASF) under one or more
4  * contributor license agreements. See the NOTICE file distributed with
5  * this work for additional information regarding copyright ownership.
6  * The ASF licenses this file to You under the Apache License, Version 2.0
7  * (the "License"); you may not use this file except in compliance with
8  * the License. You may obtain a copy of the License at
9  *
10  * http://www.apache.org/licenses/LICENSE-2.0
11  *
12  * Unless required by applicable law or agreed to in writing, software
13  * distributed under the License is distributed on an "AS IS" BASIS,
14  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15  * See the License for the specific language governing permissions and
16  * limitations under the License.
17  */
18 package org.apache.activemq.broker.region.policy;
19
20 import org.apache.activemq.broker.region.TopicSubscription;
21
22 /**
23  * A pluggable strategy to calculate the maximum number of messages that are allowed to be pending on
24  * consumers (in addition to their prefetch sizes).
25  *
26  * Once the limit is reached, non-durable topics can then start discarding old messages.
27  * This allows us to keep dispatching messages to slow consumers while not blocking fast consumers
28  * and discarding the messages oldest first.
29  *
30  * @version $Revision: 426366 $
31  */
32 public interface PendingMessageLimitStrategy {
33
34     /**
35      * Calculate the maximum number of pending messages (in excess of the prefetch size)
36      * for the given subscription
37      *
38      * @return the maximum or -1 if there is no maximum
39      */
40     int getMaximumPendingMessageLimit(TopicSubscription subscription);
41
42 }
43
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