250 lines
8.6 KiB
Java
250 lines
8.6 KiB
Java
/*
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* Copyright 2018 dorkbox, llc
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package dorkbox.collections;
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import java.io.Serializable;
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import java.util.ArrayList;
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import java.util.Collection;
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import java.util.Iterator;
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import java.util.List;
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import java.util.ListIterator;
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import java.util.RandomAccess;
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import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
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/**
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* This class uses the "single-writer-principle" for lock-free publication.
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*
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* Since there are only 2 methods to guarantee that modifications can only be called one-at-a-time (either it is only called by
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* one thread, or only one thread can access it at a time) -- we chose the 2nd option -- and use 'synchronized' to make sure that only
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* one thread can access this modification methods at a time. Getting or checking the presence of values can then happen in a lock-free
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* manner.
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*
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* According to my benchmarks, this is approximately 25% faster than ConcurrentHashMap for (all types of) reads, and a lot slower for
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* contended writes.
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*
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* This data structure is for many-read/few-write scenarios
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*/
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public final
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class LockFreeArrayList<E> implements List<E>, RandomAccess, Cloneable, Serializable {
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public static final String version = Collections.version;
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// Recommended for best performance while adhering to the "single writer principle". Must be static-final
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private static final AtomicReferenceFieldUpdater<LockFreeArrayList, ArrayList> listRef =
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AtomicReferenceFieldUpdater.newUpdater(LockFreeArrayList.class,
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ArrayList.class, "arrayList");
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private volatile ArrayList<E> arrayList = new ArrayList<>();
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public
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LockFreeArrayList(){}
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public
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LockFreeArrayList(Collection<E> elements) {
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arrayList.addAll(elements);
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}
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// synchronized is used here to ensure the "single writer principle", and make sure that ONLY one thread at a time can enter this
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// section. Because of this, we can have unlimited reader threads all going at the same time, without contention (which is our
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// use-case 99% of the time)
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public synchronized
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void clear() {
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arrayList.clear();
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}
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// synchronized is used here to ensure the "single writer principle", and make sure that ONLY one thread at a time can enter this
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// section. Because of this, we can have unlimited reader threads all going at the same time, without contention (which is our
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// use-case 99% of the time)
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public synchronized
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boolean add(final E element) {
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return arrayList.add(element);
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}
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// synchronized is used here to ensure the "single writer principle", and make sure that ONLY one thread at a time can enter this
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// section. Because of this, we can have unlimited reader threads all going at the same time, without contention (which is our
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// use-case 99% of the time)
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public synchronized
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boolean addAll(final Collection<? extends E> elements) {
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return arrayList.addAll(elements);
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}
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// synchronized is used here to ensure the "single writer principle", and make sure that ONLY one thread at a time can enter this
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// section. Because of this, we can have unlimited reader threads all going at the same time, without contention (which is our
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// use-case 99% of the time)
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@Override
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public synchronized
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boolean addAll(final int i, final Collection<? extends E> collection) {
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return arrayList.addAll(i, collection);
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}
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// synchronized is used here to ensure the "single writer principle", and make sure that ONLY one thread at a time can enter this
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// section. Because of this, we can have unlimited reader threads all going at the same time, without contention (which is our
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// use-case 99% of the time)
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@Override
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public
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boolean removeAll(final Collection<?> collection) {
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return arrayList.removeAll(collection);
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}
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// synchronized is used here to ensure the "single writer principle", and make sure that ONLY one thread at a time can enter this
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// section. Because of this, we can have unlimited reader threads all going at the same time, without contention (which is our
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// use-case 99% of the time)
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@Override
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public synchronized
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boolean retainAll(final Collection<?> collection) {
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return retainAll(collection);
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}
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@SuppressWarnings("unchecked")
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public
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E get(int index) {
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return (E) listRef.get(this).get(index);
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}
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// synchronized is used here to ensure the "single writer principle", and make sure that ONLY one thread at a time can enter this
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// section. Because of this, we can have unlimited reader threads all going at the same time, without contention (which is our
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// use-case 99% of the time)
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@Override
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public synchronized
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E set(final int index, final E element) {
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return arrayList.set(index, element);
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}
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// synchronized is used here to ensure the "single writer principle", and make sure that ONLY one thread at a time can enter this
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// section. Because of this, we can have unlimited reader threads all going at the same time, without contention (which is our
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// use-case 99% of the time)
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@Override
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public synchronized
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void add(final int index, final E element) {
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arrayList.add(index, element);
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}
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// synchronized is used here to ensure the "single writer principle", and make sure that ONLY one thread at a time can enter this
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// section. Because of this, we can have unlimited reader threads all going at the same time, without contention (which is our
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// use-case 99% of the time)
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@Override
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public synchronized
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E remove(final int index) {
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return arrayList.remove(index);
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}
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// lock-free get
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@Override
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public
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int indexOf(final Object object) {
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return listRef.get(this).indexOf(object);
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}
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// lock-free get
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@Override
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public
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int lastIndexOf(final Object object) {
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return listRef.get(this).lastIndexOf(object);
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}
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// lock-free get
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@SuppressWarnings("unchecked")
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@Override
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public
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ListIterator<E> listIterator() {
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return listRef.get(this).listIterator();
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}
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// lock-free get
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@SuppressWarnings("unchecked")
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@Override
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public
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ListIterator<E> listIterator(final int index) {
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return listRef.get(this).listIterator(index);
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}
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// lock-free get
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@SuppressWarnings("unchecked")
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@Override
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public
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List<E> subList(final int startIndex, final int endIndex) {
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return listRef.get(this).subList(startIndex, endIndex);
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}
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// synchronized is used here to ensure the "single writer principle", and make sure that ONLY one thread at a time can enter this
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// section. Because of this, we can have unlimited reader threads all going at the same time, without contention (which is our
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// use-case 99% of the time)
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public synchronized
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boolean remove(final Object element) {
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return arrayList.remove(element);
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}
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// lock-free get
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@SuppressWarnings("unchecked")
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@Override
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public
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boolean containsAll(final Collection<?> collection) {
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return listRef.get(this).containsAll(collection);
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}
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// lock-free get
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public
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int size() {
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return listRef.get(this).size();
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}
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// lock-free get
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@Override
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public
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boolean isEmpty() {
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return listRef.get(this).isEmpty();
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}
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// lock-free get
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public
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boolean contains(final Object element) {
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// use the SWP to get the value
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return listRef.get(this).contains(element);
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}
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// lock-free get
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@SuppressWarnings("unchecked")
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@Override
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public
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Iterator<E> iterator() {
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return listRef.get(this).iterator();
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}
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// lock-free get
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@Override
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public
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Object[] toArray() {
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return listRef.get(this).toArray();
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}
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// lock-free get
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@SuppressWarnings("unchecked")
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@Override
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public
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<T> T[] toArray(final T[] targetArray) {
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return (T[]) listRef.get(this).toArray(targetArray);
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}
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// lock-free get
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@SuppressWarnings("unchecked")
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public
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ArrayList<E> elements() {
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return listRef.get(this);
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}
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}
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