| /* |
| * 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.geode.internal; |
| |
| import java.io.IOException; |
| import java.io.ObjectInputStream; |
| import java.io.ObjectOutputStream; |
| import java.io.Serializable; |
| import java.util.Collection; |
| import java.util.Collections; |
| import java.util.HashSet; |
| import java.util.Iterator; |
| import java.util.LinkedList; |
| import java.util.Set; |
| import java.util.function.Consumer; |
| |
| /** |
| * A Hash set where every modification makes an internal copy of a HashSet. Similar to |
| * java.util.concurrent.CopyOnWriteArrayList, except methods provide the access time characteristics |
| * of HashSet, instead of ArrayList, for example contains is O(1) instead of O(n). |
| * |
| * Also, this class provides a getSnapshot method, which should be used for any thing that needs an |
| * unchanging snapshot of this this (For example, any serialization of this class should use |
| * getSnapshot). |
| * |
| */ |
| public class CopyOnWriteHashSet<T> implements Set<T>, Serializable { |
| |
| private static final long serialVersionUID = 8591978652141659932L; |
| |
| private transient volatile Set<T> snapshot = Collections.emptySet(); |
| |
| public CopyOnWriteHashSet() {} |
| |
| public CopyOnWriteHashSet(Set<T> copy) { |
| this.snapshot = new HashSet<T>(copy); |
| } |
| |
| /** |
| * Create a custom {@link Iterator} implementation for the {@link CopyOnWriteHashSet} |
| */ |
| @Override |
| public Iterator<T> iterator() { |
| return new Iterator<T>() { |
| |
| private Iterator<T> iterator = new LinkedList<>(snapshot).iterator(); |
| private T currentElement; |
| |
| @Override |
| public boolean hasNext() { |
| return iterator.hasNext(); |
| } |
| |
| @Override |
| public T next() { |
| currentElement = iterator.next(); |
| return currentElement; |
| } |
| |
| @Override |
| public void remove() { |
| snapshot.remove(currentElement); |
| } |
| |
| @Override |
| public void forEachRemaining(Consumer<? super T> action) { |
| iterator.forEachRemaining(action); |
| } |
| }; |
| } |
| |
| @Override |
| public int size() { |
| return snapshot.size(); |
| } |
| |
| @Override |
| public boolean add(T e) { |
| synchronized (this) { |
| Set<T> set = new HashSet<T>(snapshot); |
| boolean result = set.add(e); |
| snapshot = set; |
| return result; |
| } |
| } |
| |
| @Override |
| public boolean addAll(Collection<? extends T> c) { |
| synchronized (this) { |
| Set<T> set = new HashSet<T>(snapshot); |
| boolean result = set.addAll(c); |
| snapshot = set; |
| return result; |
| } |
| } |
| |
| @Override |
| public void clear() { |
| synchronized (this) { |
| snapshot = Collections.emptySet(); |
| } |
| } |
| |
| @Override |
| public boolean contains(Object o) { |
| return snapshot.contains(o); |
| } |
| |
| @Override |
| public boolean containsAll(Collection<?> c) { |
| return snapshot.containsAll(c); |
| } |
| |
| @Override |
| public boolean isEmpty() { |
| return snapshot.isEmpty(); |
| } |
| |
| @Override |
| public boolean remove(Object o) { |
| synchronized (this) { |
| Set<T> set = new HashSet<T>(snapshot); |
| boolean result = set.remove(o); |
| snapshot = set; |
| return result; |
| } |
| } |
| |
| @Override |
| public boolean retainAll(Collection<?> c) { |
| synchronized (this) { |
| Set<T> set = new HashSet<T>(snapshot); |
| boolean result = set.retainAll(c); |
| snapshot = set; |
| return result; |
| } |
| } |
| |
| @Override |
| public Object[] toArray() { |
| return snapshot.toArray(); |
| } |
| |
| @Override |
| public <T> T[] toArray(T[] a) { |
| return snapshot.toArray(a); |
| } |
| |
| @Override |
| public boolean equals(Object o) { |
| return snapshot.equals(o); |
| } |
| |
| @Override |
| public int hashCode() { |
| return snapshot.hashCode(); |
| } |
| |
| @Override |
| public boolean removeAll(Collection<?> c) { |
| synchronized (this) { |
| Set<T> set = new HashSet<T>(snapshot); |
| boolean result = set.removeAll(c); |
| snapshot = set; |
| return result; |
| } |
| } |
| |
| @Override |
| public String toString() { |
| return snapshot.toString(); |
| } |
| |
| /** |
| * Return a snapshot of the set at this point in time. The snapshot is guaranteed not to change. |
| * It is therefore unmodifiable. This will likely be more efficient than copying this set. |
| * |
| * @return A snapshot of this set. |
| */ |
| public Set<T> getSnapshot() { |
| return Collections.unmodifiableSet(snapshot); |
| } |
| |
| private void writeObject(ObjectOutputStream s) throws IOException { |
| s.defaultWriteObject(); |
| s.writeObject(snapshot); |
| } |
| |
| @SuppressWarnings("unchecked") |
| private void readObject(ObjectInputStream s) throws java.io.IOException, ClassNotFoundException { |
| s.defaultReadObject(); |
| this.snapshot = (Set<T>) s.readObject(); |
| } |
| |
| } |