/**
* 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.hadoop.hdfs.util;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.ArrayList;
import java.util.List;
import java.util.NoSuchElementException;
/**
* A low memory linked hash set implementation, which uses an array for storing
* the elements and linked lists for collision resolution. In addition it stores
* elements in a linked list to ensure ordered traversal. This class does not
* support null element.
*
* This class is not thread safe.
*
*/
public class LightWeightLinkedSet<T> extends LightWeightHashSet<T> {
/**
* Elements of {@link LightWeightLinkedSet}.
*/
static class DoubleLinkedElement<T> extends LinkedElement<T> {
// references to elements within all-element linked list
private DoubleLinkedElement<T> before;
private DoubleLinkedElement<T> after;
public DoubleLinkedElement(T elem, int hashCode) {
super(elem, hashCode);
this.before = null;
this.after = null;
}
@Override
public String toString() {
return super.toString();
}
}
private DoubleLinkedElement<T> head;
private DoubleLinkedElement<T> tail;
/**
* @param initCapacity
* Recommended size of the internal array.
* @param maxLoadFactor
* used to determine when to expand the internal array
* @param minLoadFactor
* used to determine when to shrink the internal array
*/
public LightWeightLinkedSet(int initCapacity, float maxLoadFactor,
float minLoadFactor) {
super(initCapacity, maxLoadFactor, minLoadFactor);
head = null;
tail = null;
}
public LightWeightLinkedSet() {
this(MINIMUM_CAPACITY, DEFAULT_MAX_LOAD_FACTOR, DEFAUT_MIN_LOAD_FACTOR);
}
/**
* Add given element to the hash table
*
* @return true if the element was not present in the table, false otherwise
*/
@Override
protected boolean addElem(final T element) {
// validate element
if (element == null) {
throw new IllegalArgumentException("Null element is not supported.");
}
// find hashCode & index
final int hashCode = element.hashCode();
final int index = getIndex(hashCode);
// return false if already present
if (getContainedElem(index, element, hashCode) != null) {
return false;
}
modification++;
size++;
// update bucket linked list
DoubleLinkedElement<T> le = new DoubleLinkedElement<T>(element, hashCode);
le.next = entries[index];
entries[index] = le;
// insert to the end of the all-element linked list
le.after = null;
le.before = tail;
if (tail != null) {
tail.after = le;
}
tail = le;
if (head == null) {
head = le;
}
return true;
}
/**
* Remove the element corresponding to the key, given key.hashCode() == index.
*
* @return Return the entry with the element if exists. Otherwise return null.
*/
@Override
protected DoubleLinkedElement<T> removeElem(final T key) {
DoubleLinkedElement<T> found = (DoubleLinkedElement<T>) (super
.removeElem(key));
if (found == null) {
return null;
}
// update linked list
if (found.after != null) {
found.after.before = found.before;
}
if (found.before != null) {
found.before.after = found.after;
}
if (head == found) {
head = head.after;
}
if (tail == found) {
tail = tail.before;
}
return found;
}
/**
* Remove and return first element on the linked list of all elements.
*
* @return first element
*/
public T pollFirst() {
if (head == null) {
return null;
}
T first = head.element;
this.remove(first);
return first;
}
/**
* Remove and return n elements from the hashtable.
* The order in which entries are removed is corresponds
* to the order in which they were inserted.
*
* @return first element
*/
@Override
public List<T> pollN(int n) {
if (n >= size) {
// if we need to remove all elements then do fast polling
return pollAll();
}
List<T> retList = new ArrayList<T>(n);
while (n-- > 0 && head != null) {
T curr = head.element;
this.removeElem(curr);
retList.add(curr);
}
shrinkIfNecessary();
return retList;
}
/**
* Remove all elements from the set and return them in order. Traverse the
* link list, don't worry about hashtable - faster version of the parent
* method.
*/
@Override
public List<T> pollAll() {
List<T> retList = new ArrayList<T>(size);
while (head != null) {
retList.add(head.element);
head = head.after;
}
this.clear();
return retList;
}
@Override
@SuppressWarnings("unchecked")
public <U> U[] toArray(U[] a) {
if (a == null) {
throw new NullPointerException("Input array can not be null");
}
if (a.length < size) {
a = (U[]) java.lang.reflect.Array.newInstance(a.getClass()
.getComponentType(), size);
}
int currentIndex = 0;
DoubleLinkedElement<T> current = head;
while (current != null) {
T curr = current.element;
a[currentIndex++] = (U) curr;
current = current.after;
}
return a;
}
@Override
public Iterator<T> iterator() {
return new LinkedSetIterator();
}
private class LinkedSetIterator implements Iterator<T> {
/** The starting modification for fail-fast. */
private final int startModification = modification;
/** The next element to return. */
private DoubleLinkedElement<T> next = head;
@Override
public boolean hasNext() {
return next != null;
}
@Override
public T next() {
if (modification != startModification) {
throw new ConcurrentModificationException("modification="
+ modification + " != startModification = " + startModification);
}
if (next == null) {
throw new NoSuchElementException();
}
final T e = next.element;
// find the next element
next = next.after;
return e;
}
@Override
public void remove() {
throw new UnsupportedOperationException("Remove is not supported.");
}
}
/**
* Clear the set. Resize it to the original capacity.
*/
@Override
public void clear() {
super.clear();
this.head = null;
this.tail = null;
}
}