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* 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.synapse.commons.executors;
import java.util.List;
/**
* This is a priority based round robin algorithm for getting the next queue </p>
*
* <p>This algorithm works in cycles. Lets say we have queues with following priorities.
* 7, 5, 2 and assume we name the queues as 1, 2, 3 in the order. </p>
* <p>Here is how messages are picked in a single cycle </p>
* <p> 1, 1, 1, 1, 1, 1, 1 all the messages for the queue with priority 1 are sent for this cycle
* 2, 2, 2, 2, 2, all the messages for the queue with priority 2 are sent for this cycle
* 3, 3 all the messages with priority 2 are sent for this cycle</p>
*
* <p>This algorithm choose the queues in the above order if all the queues have messages at the
* point of selection. If a queue doesn't have messages it will skip the queue and move to the
* next. If none of the queues have messages it will return null.
*/
public class PRRNextQueueAlgorithm<E> implements NextQueueAlgorithm<E> {
/** Reference to the actual queue */
private List<InternalQueue<E>> queues;
/** Number of queues, we keep this to avoid the overhead of calculation this again and again */
private int size = 0;
/** Current queue we are operating on */
private int currentQueue = 0;
/** Number of messages sent from the current queue */
private int currentCount = 0;
public InternalQueue<E> getNextQueue() {
InternalQueue<E> internalQueue = queues.get(currentQueue);
int priority = internalQueue.getPriority();
if (priority == currentCount || internalQueue.size() == 0) {
currentCount = 0;
// we need to move to the next queue not empty
int c = 0;
do {
if (currentQueue == queues.size() - 1) {
currentQueue = 0;
} else {
currentQueue++;
}
internalQueue = queues.get(currentQueue);
c++;
// we move forward until we find a non empty queue or everything is empty
} while (internalQueue.size() == 0 && c < size);
// if we come to the initial queue, that means all the queues are empty.
if (internalQueue.size() == 0) {
currentQueue = 0;
return null;
}
}
currentCount++;
return internalQueue;
}
public void init(List<InternalQueue<E>> queues) {
this.queues = queues;
size = queues.size();
}
}