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/*
* Copyright 2014 Ben Manes. All Rights Reserved.
*
* Licensed 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 com.github.benmanes.caffeine.cache;
import java.util.AbstractCollection;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.NoSuchElementException;
import org.checkerframework.checker.nullness.qual.Nullable;
/**
* This class provides a skeletal implementation of the {@link LinkedDeque} interface to minimize
* the effort required to implement this interface.
*
* @author [email protected] (Ben Manes)
* @param the type of elements held in this collection
*/
abstract class AbstractLinkedDeque extends AbstractCollection implements LinkedDeque {
// This class provides a doubly-linked list that is optimized for the virtual machine. The first
// and last elements are manipulated instead of a slightly more convenient sentinel element to
// avoid the insertion of null checks with NullPointerException throws in the byte code. The links
// to a removed element are cleared to help a generational garbage collector if the discarded
// elements inhabit more than one generation.
/**
* Pointer to first node.
* Invariant: (first == null && last == null) ||
* (first.prev == null)
*/
@Nullable E first;
/**
* Pointer to last node.
* Invariant: (first == null && last == null) ||
* (last.next == null)
*/
@Nullable E last;
/**
* The number of times this deque has been structurally modified. Structural modifications
* are those that change the size of the deque, or otherwise perturb it in such a fashion that
* iterations in progress may yield incorrect results.
*/
int modCount;
/**
* Links the element to the front of the deque so that it becomes the first element.
*
* @param e the unlinked element
*/
void linkFirst(final E e) {
final E f = first;
first = e;
if (f == null) {
last = e;
} else {
setPrevious(f, e);
setNext(e, f);
}
modCount++;
}
/**
* Links the element to the back of the deque so that it becomes the last element.
*
* @param e the unlinked element
*/
void linkLast(final E e) {
final E l = last;
last = e;
if (l == null) {
first = e;
} else {
setNext(l, e);
setPrevious(e, l);
}
modCount++;
}
/** Unlinks the non-null first element. */
@SuppressWarnings("NullAway")
E unlinkFirst() {
final E f = first;
final E next = getNext(f);
setNext(f, null);
first = next;
if (next == null) {
last = null;
} else {
setPrevious(next, null);
}
modCount++;
return f;
}
/** Unlinks the non-null last element. */
@SuppressWarnings("NullAway")
E unlinkLast() {
final E l = last;
final E prev = getPrevious(l);
setPrevious(l, null);
last = prev;
if (prev == null) {
first = null;
} else {
setNext(prev, null);
}
modCount++;
return l;
}
/** Unlinks the non-null element. */
void unlink(E e) {
final E prev = getPrevious(e);
final E next = getNext(e);
if (prev == null) {
first = next;
} else {
setNext(prev, next);
setPrevious(e, null);
}
if (next == null) {
last = prev;
} else {
setPrevious(next, prev);
setNext(e, null);
}
modCount++;
}
@Override
public boolean isEmpty() {
return (first == null);
}
void checkNotEmpty() {
if (isEmpty()) {
throw new NoSuchElementException();
}
}
/**
* {@inheritDoc}
*
* Beware that, unlike in most collections, this method is NOT a constant-time operation.
*/
@Override
public int size() {
int size = 0;
for (E e = first; e != null; e = getNext(e)) {
size++;
}
return size;
}
@Override
@SuppressWarnings("PMD.AvoidReassigningLoopVariables")
public void clear() {
E e = first;
while (e != null) {
E next = getNext(e);
setPrevious(e, null);
setNext(e, null);
e = next;
}
first = last = null;
modCount++;
}
@Override
public abstract boolean contains(Object o);
@Override
public boolean isFirst(E e) {
return (e != null) && (e == first);
}
@Override
public boolean isLast(E e) {
return (e != null) && (e == last);
}
@Override
public void moveToFront(E e) {
if (e != first) {
unlink(e);
linkFirst(e);
}
}
@Override
public void moveToBack(E e) {
if (e != last) {
unlink(e);
linkLast(e);
}
}
@Override
public @Nullable E peek() {
return peekFirst();
}
@Override
public @Nullable E peekFirst() {
return first;
}
@Override
public @Nullable E peekLast() {
return last;
}
@Override
@SuppressWarnings("NullAway")
public E getFirst() {
checkNotEmpty();
return peekFirst();
}
@Override
@SuppressWarnings("NullAway")
public E getLast() {
checkNotEmpty();
return peekLast();
}
@Override
public E element() {
return getFirst();
}
@Override
public boolean offer(E e) {
return offerLast(e);
}
@Override
public boolean offerFirst(E e) {
if (contains(e)) {
return false;
}
linkFirst(e);
return true;
}
@Override
public boolean offerLast(E e) {
if (contains(e)) {
return false;
}
linkLast(e);
return true;
}
@Override
public boolean add(E e) {
return offerLast(e);
}
@Override
public void addFirst(E e) {
if (!offerFirst(e)) {
throw new IllegalArgumentException();
}
}
@Override
public void addLast(E e) {
if (!offerLast(e)) {
throw new IllegalArgumentException();
}
}
@Override
public @Nullable E poll() {
return pollFirst();
}
@Override
public @Nullable E pollFirst() {
return isEmpty() ? null : unlinkFirst();
}
@Override
public @Nullable E pollLast() {
return isEmpty() ? null : unlinkLast();
}
@Override
public E remove() {
return removeFirst();
}
@Override
@SuppressWarnings("NullAway")
public E removeFirst() {
checkNotEmpty();
return pollFirst();
}
@Override
public abstract boolean remove(Object o);
@Override
public boolean removeFirstOccurrence(Object o) {
return remove(o);
}
@Override
@SuppressWarnings("NullAway")
public E removeLast() {
checkNotEmpty();
return pollLast();
}
@Override
public boolean removeLastOccurrence(Object o) {
return remove(o);
}
@Override
public boolean removeAll(Collection c) {
boolean modified = false;
for (Object o : c) {
modified |= remove(o);
}
return modified;
}
@Override
public void push(E e) {
addFirst(e);
}
@Override
public E pop() {
return removeFirst();
}
@Override
public PeekingIterator iterator() {
return new AbstractLinkedIterator(first) {
@SuppressWarnings("NullAway")
@Override @Nullable E computeNext() {
return getNext(cursor);
}
};
}
@Override
public PeekingIterator descendingIterator() {
return new AbstractLinkedIterator(last) {
@SuppressWarnings("NullAway")
@Override @Nullable E computeNext() {
return getPrevious(cursor);
}
};
}
abstract class AbstractLinkedIterator implements PeekingIterator {
@Nullable E previous;
@Nullable E cursor;
int expectedModCount;
/**
* Creates an iterator that can can traverse the deque.
*
* @param start the initial element to begin traversal from
*/
AbstractLinkedIterator(@Nullable E start) {
expectedModCount = modCount;
cursor = start;
}
@Override
public boolean hasNext() {
checkForComodification();
return (cursor != null);
}
@Override
public @Nullable E peek() {
return cursor;
}
@Override
@SuppressWarnings("NullAway")
public E next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
previous = cursor;
cursor = computeNext();
return previous;
}
/** Retrieves the next element to traverse to or null if there are no more elements. */
abstract @Nullable E computeNext();
@Override
public void remove() {
if (previous == null) {
throw new IllegalStateException();
}
checkForComodification();
AbstractLinkedDeque.this.remove(previous);
expectedModCount = modCount;
previous = null;
}
/**
* If the expected modCount value that the iterator believes that the backing deque should have
* is violated then the iterator has detected concurrent modification.
*/
void checkForComodification() {
if (modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
}
}
}