| package org.apache.helix.common; |
| |
| /* |
| * 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. |
| */ |
| |
| import java.util.Map; |
| import java.util.Queue; |
| import java.util.concurrent.BlockingQueue; |
| |
| import com.google.common.collect.Lists; |
| import com.google.common.collect.Maps; |
| |
| /** |
| * A blocking queue of events, which automatically deduplicate events with the same "type" within |
| * the queue, i.e, when putting an event into the queue, if there is already an event with the |
| * same type existing in the queue, the new event won't be inserted into the queue. |
| * This class is meant to be a limited implementation of the {@link BlockingQueue} interface. |
| * |
| * T -- the Type of an event. |
| * E -- the event itself. |
| */ |
| public class DedupEventBlockingQueue<T, E> { |
| private final Map<T, Entry<T, E>> _eventMap; |
| private final Queue<Entry> _eventQueue; |
| |
| class Entry <T, E> { |
| private T _type; |
| private E _event; |
| |
| Entry (T type, E event) { |
| _type = type; |
| _event = event; |
| } |
| |
| T getType() { |
| return _type; |
| } |
| |
| E getEvent() { |
| return _event; |
| } |
| } |
| |
| /** |
| * Instantiate the queue |
| */ |
| public DedupEventBlockingQueue() { |
| _eventMap = Maps.newHashMap(); |
| _eventQueue = Lists.newLinkedList(); |
| } |
| |
| /** |
| * Remove all events from the queue |
| */ |
| public synchronized void clear() { |
| _eventMap.clear(); |
| _eventQueue.clear(); |
| } |
| |
| /** |
| * Add a single event to the queue, overwriting events with the same name |
| */ |
| public synchronized void put(T type, E event) { |
| Entry entry = new Entry(type, event); |
| |
| if (!_eventMap.containsKey(entry.getType())) { |
| // only insert to the queue if there isn't a same-typed event already present |
| boolean result = _eventQueue.offer(entry); |
| if (!result) { |
| return; |
| } |
| } |
| // always overwrite the existing entry in the map in case the entry is different |
| _eventMap.put((T) entry.getType(), entry); |
| notify(); |
| } |
| |
| /** |
| * Remove an element from the front of the queue, blocking if none is available. This method |
| * will return the most recent event seen with the oldest enqueued event name. |
| * @return ClusterEvent at the front of the queue |
| * @throws InterruptedException if the wait for elements was interrupted |
| */ |
| public synchronized E take() throws InterruptedException { |
| while (_eventQueue.isEmpty()) { |
| wait(); |
| } |
| Entry entry = _eventQueue.poll(); |
| if (entry != null) { |
| entry = _eventMap.remove(entry.getType()); |
| return (E) entry.getEvent(); |
| } |
| return null; |
| } |
| |
| /** |
| * Get at the head of the queue without removing it |
| * @return ClusterEvent at the front of the queue, or null if none available |
| */ |
| public synchronized E peek() { |
| Entry entry = _eventQueue.peek(); |
| if (entry != null) { |
| entry = _eventMap.get(entry.getType()); |
| return (E) entry.getEvent(); |
| } |
| return null; |
| } |
| |
| /** |
| * Get the queue size |
| * @return integer size of the queue |
| */ |
| public int size() { |
| return _eventQueue.size(); |
| } |
| |
| /** |
| * Check if the queue is empty |
| * @return true if events are not present, false otherwise |
| */ |
| public boolean isEmpty() { |
| return _eventQueue.isEmpty(); |
| } |
| } |