001    /**
002     * Licensed to the Apache Software Foundation (ASF) under one
003     * or more contributor license agreements.  See the NOTICE file
004     * distributed with this work for additional information
005     * regarding copyright ownership.  The ASF licenses this file
006     * to you under the Apache License, Version 2.0 (the
007     * "License"); you may not use this file except in compliance
008     * with the License.  You may obtain a copy of the License at
009     *
010     *      http://www.apache.org/licenses/LICENSE-2.0
011     *
012     * Unless required by applicable law or agreed to in writing, software
013     * distributed under the License is distributed on an "AS IS" BASIS,
014     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015     * See the License for the specific language governing permissions and
016     * limitations under the License.
017     */
018    package org.apache.oozie.event;
019    
020    import java.io.Serializable;
021    import java.util.List;
022    
023    import org.apache.hadoop.conf.Configuration;
024    import org.apache.oozie.client.event.Event;
025    
026    /**
027     * Interface to define the queue operations for the events system
028     */
029    public interface EventQueue {
030    
031        public class EventQueueElement implements Serializable {
032    
033            private static final long serialVersionUID = 1L;
034            Event event;
035    
036            public EventQueueElement(Event e) {
037                event = e;
038            }
039        }
040    
041        /**
042         * Initialize the event queue
043         * @param conf
044         */
045        public void init(Configuration conf);
046    
047        /**
048         * Add event to queue
049         * @param event
050         */
051        public void add(Event e);
052    
053        /**
054         * Fetch events from queue in batch
055         * @return events set
056         */
057        public List<Event> pollBatch();
058    
059        /**
060        * Fetch single event from queue
061        * @return event
062        */
063       public Event poll();
064    
065        /**
066         * Find out if queue is empty
067         * @return boolean
068         */
069        public boolean isEmpty();
070    
071        /**
072         * Get current queue size
073         * @return size
074         */
075        public int size();
076    
077        /**
078         * Read topmost event from queue but do not pop from it
079         * @return event
080         */
081        public Event peek();
082    
083        /**
084         * Get the batch size used during polling events
085         * @return batchSize
086         */
087        public int getBatchSize();
088    
089        /**
090         * Clear the events queue
091         */
092        public void clear();
093    
094    }