001/**
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.activemq.broker.region.cursors;
018
019import java.util.Collection;
020import java.util.Iterator;
021
022import org.apache.activemq.broker.region.MessageReference;
023
024public interface PendingList extends Iterable<MessageReference> {
025
026    /**
027     * Returns true if there are no Messages in the PendingList currently.
028     * @return true if the PendingList is currently empty.
029     */
030    public boolean isEmpty();
031
032    /**
033     * Discards all Messages currently held in the PendingList.
034     */
035    public void clear();
036
037    /**
038     * Adds the given message to the head of the list.
039     *
040     * @param message
041     *      The MessageReference that is to be added to this list.
042     *
043     * @return the PendingNode that contains the newly added message.
044     */
045    public PendingNode addMessageFirst(MessageReference message);
046
047    /**
048     * Adds the given message to the tail of the list.
049     *
050     * @param message
051     *      The MessageReference that is to be added to this list.
052     *
053     * @return the PendingNode that contains the newly added message.
054     */
055    public PendingNode addMessageLast(MessageReference message);
056
057    /**
058     * Removes the given MessageReference from the PendingList if it is
059     * contained within.
060     *
061     * @param message
062     *      The MessageReference that is to be removed to this list.
063     *
064     * @return the PendingNode that contains the removed message or null if the
065     *         message was not present in this list.
066     */
067    public PendingNode remove(MessageReference message);
068
069    /**
070     * Returns the number of MessageReferences that are awaiting dispatch.
071     * @return current count of the pending messages.
072     */
073    public int size();
074
075    /**
076     * Returns an iterator over the pending Messages.  The subclass controls how
077     * the returned iterator actually traverses the list of pending messages allowing
078     * for the order to vary based on factors like Message priority or some other
079     * mechanism.
080     *
081     * @return an Iterator that returns MessageReferences contained in this list.
082     */
083    public Iterator<MessageReference> iterator();
084
085    /**
086     * Query the PendingList to determine if the given message is contained within.
087     *
088     * @param message
089     *      The Message that is the target of this query.
090     *
091     * @return true if the MessageReference is contained in this list.
092     */
093    public boolean contains(MessageReference message);
094
095    /**
096     * Returns a new Collection that contains all the MessageReferences currently
097     * held in this PendingList.  The elements of the list are ordered using the
098     * same rules as the subclass uses for iteration.
099     *
100     * @return a new Collection containing this lists MessageReferences.
101     */
102    public Collection<MessageReference> values();
103
104    /**
105     * Adds all the elements of the given PendingList to this PendingList.
106     *
107     * @param pendingList
108     *      The PendingList that is to be added to this collection.
109     */
110    public void addAll(PendingList pendingList);
111}