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#ifndef QPID_BROKER_QUEUEOBSERVER_H
#define QPID_BROKER_QUEUEOBSERVER_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.
*
*/
namespace qpid {
namespace broker {
class Consumer;
class Message;
/**
* Interface for notifying classes who want to act as 'observers' of a queue of particular
* events.
*
* The events that are monitored reflect the relationship between a particular message and
* the queue it has been delivered to. A message can be considered in one of three states
* with respect to the queue:
*
* 1) "Available" - available for transfer to consumers (i.e. for browse or acquire),
*
* 2) "Acquired" - owned by a particular consumer, no longer available to other consumers
* (by either browse or acquire), but still considered on the queue.
*
* 3) "Dequeued" - removed from the queue and no longer available to any consumer.
*
* The queue events that are observable are:
*
* "Enqueued" - the message is "Available" - on the queue for transfer to any consumer
* (e.g. browse or acquire)
*
* "Acquired" - - a consumer has claimed exclusive access to it. It is no longer available
* for other consumers to browse or acquire, but it is not yet considered dequeued as it
* may be requeued by the consumer.
*
* "Requeued" - a previously-acquired message is released by its owner: it is put back on
* the queue at its original position and returns to the "Available" state.
*
* "Dequeued" - a message is no longer queued. At this point, the queue no longer tracks
* the message, and the broker considers the consumer's transaction complete.
*/
class QueueObserver
{
public:
virtual ~QueueObserver() {}
// note: the Queue will hold the messageLock while calling these methods!
virtual void enqueued(const Message&) = 0;
virtual void dequeued(const Message&) = 0;
virtual void acquired(const Message&) = 0;
virtual void requeued(const Message&) = 0;
virtual void consumerAdded( const Consumer& ) {};
virtual void consumerRemoved( const Consumer& ) {};
private:
};
}} // namespace qpid::broker
#endif /*!QPID_BROKER_QUEUEOBSERVER_H*/
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