| /* |
| * 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. |
| */ |
| package org.apache.gossip.crdt; |
| |
| import java.util.Arrays; |
| import java.util.HashMap; |
| import java.util.HashSet; |
| import java.util.Map; |
| import java.util.Set; |
| import java.util.function.Function; |
| import java.util.stream.Collectors; |
| import java.util.stream.Stream; |
| |
| /* |
| Max Change Set CrdtSet. Value which has changed the most wins. |
| You cannot delete an element which is not present, and cannot add an element which is already present. |
| MC-sets are compact and do the right thing when changes to elements are infrequent compared to the gossiping period. |
| |
| Read more: https://github.com/aphyr/meangirls#max-change-sets |
| You can view examples of usage in tests: |
| MaxChangeSetTest - unit tests |
| DataTest - integration test with 2 nodes, MaxChangeSet was serialized/deserialized, sent between nodes, merged |
| */ |
| |
| public class MaxChangeSet<ElementType> implements CrdtAddRemoveSet<ElementType, Set<ElementType>, MaxChangeSet<ElementType>> { |
| private final Map<ElementType, Integer> struct; |
| |
| public MaxChangeSet(){ |
| struct = new HashMap<>(); |
| } |
| |
| @SafeVarargs |
| public MaxChangeSet(ElementType... elements){ |
| this(new HashSet<>(Arrays.asList(elements))); |
| } |
| |
| public MaxChangeSet(Set<ElementType> set){ |
| struct = new HashMap<>(); |
| for (ElementType e : set){ |
| struct.put(e, 1); |
| } |
| } |
| |
| public MaxChangeSet(MaxChangeSet<ElementType> first, MaxChangeSet<ElementType> second){ |
| Function<ElementType, Integer> valueFor = element -> |
| Math.max(first.struct.getOrDefault(element, 0), second.struct.getOrDefault(element, 0)); |
| struct = Stream.concat(first.struct.keySet().stream(), second.struct.keySet().stream()) |
| .distinct().collect(Collectors.toMap(p -> p, valueFor)); |
| } |
| |
| // for serialization |
| MaxChangeSet(Map<ElementType, Integer> struct){ |
| this.struct = struct; |
| } |
| |
| Map<ElementType, Integer> getStruct(){ |
| return struct; |
| } |
| |
| private MaxChangeSet<ElementType> increment(ElementType e){ |
| Map<ElementType, Integer> changeMap = new HashMap<>(); |
| changeMap.put(e, struct.getOrDefault(e, 0) + 1); |
| return this.merge(new MaxChangeSet<>(changeMap)); |
| } |
| |
| public MaxChangeSet<ElementType> add(ElementType e){ |
| if (struct.getOrDefault(e, 0) % 2 == 1){ |
| return this; |
| } |
| return increment(e); |
| } |
| |
| public MaxChangeSet<ElementType> remove(ElementType e){ |
| if (struct.getOrDefault(e, 0) % 2 == 0){ |
| return this; |
| } |
| return increment(e); |
| } |
| |
| @Override |
| public MaxChangeSet<ElementType> merge(MaxChangeSet<ElementType> other){ |
| return new MaxChangeSet<>(this, other); |
| } |
| |
| @Override |
| public Set<ElementType> value(){ |
| return struct.entrySet().stream() |
| .filter(entry -> (entry.getValue() % 2 == 1)) |
| .map(Map.Entry::getKey) |
| .collect(Collectors.toSet()); |
| } |
| |
| @Override |
| public MaxChangeSet<ElementType> optimize(){ |
| return this; |
| } |
| |
| @Override |
| public boolean equals(Object obj){ |
| return this == obj || (obj != null && getClass() == obj.getClass() && value().equals(((MaxChangeSet) obj).value())); |
| } |
| } |