cpp/src/qpid/ha/QueueRange.h

#ifndef QPID_HA_QUEUERANGE_H
#define QPID_HA_QUEUERANGE_H

/*
 *
 * 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.
 *
 */

#include "ReplicatingSubscription.h"
#include "qpid/broker/Queue.h"
#include "qpid/broker/QueueCursor.h"
#include "qpid/framing/FieldTable.h"
#include "qpid/framing/SequenceNumber.h"
#include <iostream>

namespace qpid {
namespace ha {

/**
 * Get the front/back range of a queue or from a ReplicatingSubscription arguments table.
 *
 * The *back* of the queue is the position of the latest (most recently pushed)
 * message on the queue or, if the queue is empty, the back is n-1 where n is
 * the position that will be assigned to the next message pushed onto the queue.
 *
 * The *front* of the queue is the position of the oldest (next to be consumed) message
 * on the queue or, if the queue is empty, it is the position that will be occupied
 * by the next message pushed onto the queue.
 *
 * This leads to the slightly surprising conclusion that for an empty queue
 * front = back+1
 */
struct QueueRange {
  public:
    framing::SequenceNumber front, back;

    QueueRange() : front(1), back(0) { } // Empty range.

    QueueRange(broker::Queue& q) { q.getRange(front, back, broker::REPLICATOR); }

    QueueRange(const framing::FieldTable& args) {
        back = args.getAsInt(ReplicatingSubscription::QPID_BACK);
        front = back+1;
        if (args.isSet(ReplicatingSubscription::QPID_FRONT))
            front = args.getAsInt(ReplicatingSubscription::QPID_FRONT);
        if (back+1 < front)
            throw Exception(QPID_MSG("Invalid range [" << front << "," << back <<"]"));
    }

    bool empty() const { return front == back+1; }
};


inline std::ostream& operator<<(std::ostream& o, const QueueRange& qr) {
    if (qr.front > qr.back) return o << "[-," << qr.back << "]";
    else return o << "[" << qr.front << "," << qr.back << "]";
}


}} // namespace qpid::ha

#endif  /*!QPID_HA_QUEUERANGE_H*/