dubbo BitList 源码
dubbo BitList 代码
文件路径：/dubbo-cluster/src/main/java/org/apache/dubbo/rpc/cluster/router/state/BitList.java
/*
* 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.dubbo.rpc.cluster.router.state;
import org.apache.dubbo.common.utils.CollectionUtils;
import java.util.AbstractList;
import java.util.ArrayList;
import java.util.BitSet;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;
import java.util.NoSuchElementException;
import java.util.concurrent.ThreadLocalRandom;
/**
* BitList based on BitMap implementation.
* BitList is consists of `originList`, `rootSet` and `tailList`.
* <p>
* originList: Initial elements of the list. This list will not be changed
* in modification actions (expect clear all).
* rootSet: A bitMap to store the indexes of originList are still exist.
* Most of the modification actions are operated on this bitMap.
* tailList: An additional list for BitList. Worked when adding totally new
* elements to list. These elements will be appended to the last
* of the BitList.
* <p>
* An example of BitList:
* originList: A B C D E (5 elements)
* rootSet: x v x v v
* 0 1 0 1 1 (5 elements)
* tailList: F G H (3 elements)
* resultList: B D E F G H (6 elements)
*
* @param <E>
* @since 3.0
*/
public class BitList<E> extends AbstractList<E> {
private final BitSet rootSet;
private volatile List<E> originList;
private final static BitList emptyList = new BitList(Collections.emptyList());
private volatile List<E> tailList = null;
public BitList(List<E> originList) {
this(originList, false);
}
public BitList(List<E> originList, boolean empty) {
if (originList instanceof BitList) {
this.originList = ((BitList<E>) originList).getOriginList();
this.tailList = ((BitList<E>) originList).getTailList();
} else {
this.originList = originList;
}
this.rootSet = new BitSet();
if (!empty) {
this.rootSet.set(0, originList.size());
} else {
this.tailList = null;
}
}
public BitList(List<E> originList, boolean empty, List<E> tailList) {
this.originList = originList;
this.rootSet = new BitSet();
if (!empty) {
this.rootSet.set(0, originList.size());
}
this.tailList = tailList;
}
public BitList(List<E> originList, BitSet rootSet, List<E> tailList) {
this.originList = originList;
this.rootSet = rootSet;
this.tailList = tailList;
}
// Provided by BitList only
public List<E> getOriginList() {
return originList;
}
public void addIndex(int index) {
this.rootSet.set(index);
}
public int totalSetSize() {
return this.originList.size();
}
public boolean indexExist(int index) {
return this.rootSet.get(index);
}
public E getByIndex(int index) {
return this.originList.get(index);
}
/**
* And operation between two bitList. Return a new cloned list.
* TailList in source bitList will be totally saved even if it is not appeared in the target bitList.
*
* @param target target bitList
* @return a new bitList only contains those elements contain in both two list and source bitList's tailList
*/
public BitList<E> and(BitList<E> target) {
rootSet.and(target.rootSet);
return this;
}
public BitList<E> or(BitList<E> target) {
BitSet resultSet = (BitSet) rootSet.clone();
resultSet.or(target.rootSet);
return new BitList<>(originList, resultSet, tailList);
}
public boolean hasMoreElementInTailList() {
return CollectionUtils.isNotEmpty(tailList);
}
public List<E> getTailList() {
return tailList;
}
public void addToTailList(E e) {
if (tailList == null) {
tailList = new LinkedList<>();
}
tailList.add(e);
}
public E randomSelectOne() {
int originSize = originList.size();
int tailSize = tailList != null ? tailList.size() : 0;
int totalSize = originSize + tailSize;
int cardinality = rootSet.cardinality();
// example 1 : origin size is 1000, cardinality is 50, rate is 1/20. 20 * 2 = 40 < 50, try random select
// example 2 : origin size is 1000, cardinality is 25, rate is 1/40. 40 * 2 = 80 > 50, directly use iterator
int rate = originSize / cardinality;
if (rate <= cardinality * 2) {
int count = rate * 5;
for (int i = 0; i < count; i++) {
int random = ThreadLocalRandom.current().nextInt(totalSize);
if (random < originSize) {
if (rootSet.get(random)) {
return originList.get(random);
}
} else {
return tailList.get(random - originSize);
}
}
}
return get(ThreadLocalRandom.current().nextInt(cardinality + tailSize));
}
@SuppressWarnings("unchecked")
public static <T> BitList<T> emptyList() {
return emptyList;
}
// Provided by JDK List interface
@Override
public int size() {
return rootSet.cardinality() + (CollectionUtils.isNotEmpty(tailList) ? tailList.size() : 0);
}
@Override
public boolean contains(Object o) {
int idx = originList.indexOf(o);
return (idx >= 0 && rootSet.get(idx)) || (CollectionUtils.isNotEmpty(tailList) && tailList.contains(o));
}
@Override
public Iterator<E> iterator() {
return new BitListIterator<>(this, 0);
}
/**
* If the element to added is appeared in originList even if it is not in rootSet,
* directly set its index in rootSet to true. (This may change the order of elements.)
* <p>
* If the element is not contained in originList, allocate tailList and add to tailList.
* <p>
* Notice: It is not recommended adding duplicated element.
*/
@Override
public boolean add(E e) {
int index = originList.indexOf(e);
if (index > -1) {
rootSet.set(index);
return true;
} else {
if (tailList == null) {
tailList = new LinkedList<>();
}
return tailList.add(e);
}
}
/**
* If the element to added is appeared in originList,
* directly set its index in rootSet to false. (This may change the order of elements.)
* <p>
* If the element is not contained in originList, try to remove from tailList.
*/
@Override
public boolean remove(Object o) {
int idx = originList.indexOf(o);
if (idx > -1 && rootSet.get(idx)) {
rootSet.set(idx, false);
return true;
}
if (CollectionUtils.isNotEmpty(tailList)) {
return tailList.remove(o);
}
return false;
}
/**
* Caution: This operation will clear originList for removing references purpose.
* This may change the default behaviour when adding new element later.
*/
@Override
public void clear() {
rootSet.clear();
// to remove references
originList = Collections.emptyList();
if (CollectionUtils.isNotEmpty(tailList)) {
tailList = null;
}
}
@Override
public E get(int index) {
int bitIndex = -1;
if (index < 0) {
throw new IndexOutOfBoundsException();
}
if (index >= rootSet.cardinality()) {
if (CollectionUtils.isNotEmpty(tailList)) {
return tailList.get(index - rootSet.cardinality());
} else {
throw new IndexOutOfBoundsException();
}
} else {
for (int i = 0; i <= index; i++) {
bitIndex = rootSet.nextSetBit(bitIndex + 1);
}
return originList.get(bitIndex);
}
}
@Override
public E remove(int index) {
int bitIndex = -1;
if (index >= rootSet.cardinality()) {
if (CollectionUtils.isNotEmpty(tailList)) {
return tailList.remove(index - rootSet.cardinality());
} else {
throw new IndexOutOfBoundsException();
}
} else {
for (int i = 0; i <= index; i++) {
bitIndex = rootSet.nextSetBit(bitIndex + 1);
}
rootSet.set(bitIndex, false);
return originList.get(bitIndex);
}
}
@Override
public int indexOf(Object o) {
int bitIndex = -1;
for (int i = 0; i < rootSet.cardinality(); i++) {
bitIndex = rootSet.nextSetBit(bitIndex + 1);
if (originList.get(bitIndex).equals(o)) {
return i;
}
}
if (CollectionUtils.isNotEmpty(tailList)) {
int indexInTailList = tailList.indexOf(o);
if (indexInTailList != -1) {
return indexInTailList + rootSet.cardinality();
} else {
return -1;
}
}
return -1;
}
@Override
@SuppressWarnings("unchecked")
public boolean addAll(Collection<? extends E> c) {
if (c instanceof BitList) {
rootSet.or(((BitList<? extends E>) c).rootSet);
if (((BitList<? extends E>) c).hasMoreElementInTailList()) {
for (E e : ((BitList<? extends E>) c).tailList) {
addToTailList(e);
}
}
return true;
}
return super.addAll(c);
}
@Override
public int lastIndexOf(Object o) {
int bitIndex = -1;
int index = -1;
if (CollectionUtils.isNotEmpty(tailList)) {
int indexInTailList = tailList.lastIndexOf(o);
if (indexInTailList > -1) {
return indexInTailList + rootSet.cardinality();
}
}
for (int i = 0; i < rootSet.cardinality(); i++) {
bitIndex = rootSet.nextSetBit(bitIndex + 1);
if (originList.get(bitIndex).equals(o)) {
index = i;
}
}
return index;
}
@Override
public boolean isEmpty() {
return this.rootSet.isEmpty() && CollectionUtils.isEmpty(tailList);
}
@Override
public ListIterator<E> listIterator() {
return new BitListIterator<>(this, 0);
}
@Override
public ListIterator<E> listIterator(int index) {
return new BitListIterator<>(this, index);
}
@Override
public BitList<E> subList(int fromIndex, int toIndex) {
BitSet resultSet = (BitSet) rootSet.clone();
List<E> copiedTailList = tailList == null ? null : new LinkedList<>(tailList);
if (toIndex < size()) {
if (toIndex < rootSet.cardinality()) {
copiedTailList = null;
resultSet.set(toIndex, resultSet.length(), false);
} else {
copiedTailList = copiedTailList == null ? null : copiedTailList.subList(0, toIndex - rootSet.cardinality());
}
}
if (fromIndex > 0) {
if (fromIndex < rootSet.cardinality()) {
resultSet.set(0, fromIndex, false);
} else {
resultSet.clear();
copiedTailList = copiedTailList == null ? null : copiedTailList.subList(fromIndex - rootSet.cardinality(), copiedTailList.size());
}
}
return new BitList<>(originList, resultSet, copiedTailList);
}
public static class BitListIterator<E> implements ListIterator<E> {
private BitList<E> bitList;
private int index;
private ListIterator<E> tailListIterator;
private int curBitIndex = -1;
private boolean isInTailList = false;
private int lastReturnedIndex = -1;
public BitListIterator(BitList<E> bitList, int index) {
this.bitList = bitList;
this.index = index - 1;
for (int i = 0; i < index; i++) {
if (!isInTailList) {
curBitIndex = bitList.rootSet.nextSetBit(curBitIndex + 1);
if (curBitIndex == -1) {
if (CollectionUtils.isNotEmpty(bitList.tailList)) {
isInTailList = true;
tailListIterator = bitList.tailList.listIterator();
tailListIterator.next();
} else {
break;
}
}
} else {
tailListIterator.next();
}
}
}
@Override
public boolean hasNext() {
if (isInTailList) {
return tailListIterator.hasNext();
} else {
int nextBit = bitList.rootSet.nextSetBit(curBitIndex + 1);
if (nextBit == -1) {
return bitList.hasMoreElementInTailList();
} else {
return true;
}
}
}
@Override
public E next() {
if (isInTailList) {
if (tailListIterator.hasNext()) {
index += 1;
lastReturnedIndex = index;
}
return tailListIterator.next();
} else {
int nextBitIndex = bitList.rootSet.nextSetBit(curBitIndex + 1);
if (nextBitIndex == -1) {
if (bitList.hasMoreElementInTailList()) {
tailListIterator = bitList.tailList.listIterator();
isInTailList = true;
index += 1;
lastReturnedIndex = index;
return tailListIterator.next();
} else {
throw new NoSuchElementException();
}
} else {
index += 1;
lastReturnedIndex = index;
curBitIndex = nextBitIndex;
return bitList.originList.get(nextBitIndex);
}
}
}
@Override
public boolean hasPrevious() {
if (isInTailList) {
boolean hasPreviousInTailList = tailListIterator.hasPrevious();
if (hasPreviousInTailList) {
return true;
} else {
return bitList.rootSet.previousSetBit(bitList.rootSet.size()) != -1;
}
} else {
return curBitIndex != -1;
}
}
@Override
public E previous() {
if (isInTailList) {
boolean hasPreviousInTailList = tailListIterator.hasPrevious();
if (hasPreviousInTailList) {
lastReturnedIndex = index;
index -= 1;
return tailListIterator.previous();
} else {
int lastIndexInBit = bitList.rootSet.previousSetBit(bitList.rootSet.size());
if (lastIndexInBit == -1) {
throw new NoSuchElementException();
} else {
isInTailList = false;
curBitIndex = bitList.rootSet.previousSetBit(lastIndexInBit - 1);
lastReturnedIndex = index;
index -= 1;
return bitList.originList.get(lastIndexInBit);
}
}
} else {
if (curBitIndex == -1) {
throw new NoSuchElementException();
}
int nextBitIndex = curBitIndex;
curBitIndex = bitList.rootSet.previousSetBit(curBitIndex - 1);
lastReturnedIndex = index;
index -= 1;
return bitList.originList.get(nextBitIndex);
}
}
@Override
public int nextIndex() {
return hasNext() ? index + 1 : index;
}
@Override
public int previousIndex() {
return index;
}
@Override
public void remove() {
if (lastReturnedIndex == -1) {
throw new IllegalStateException();
} else {
if (lastReturnedIndex >= bitList.rootSet.cardinality()) {
tailListIterator.remove();
} else {
int bitIndex = -1;
for (int i = 0; i <= lastReturnedIndex; i++) {
bitIndex = bitList.rootSet.nextSetBit(bitIndex + 1);
}
bitList.rootSet.set(bitIndex, false);
}
}
if (lastReturnedIndex <= index) {
index -= 1;
}
}
@Override
public void set(E e) {
throw new UnsupportedOperationException("Set method is not supported in BitListIterator!");
}
@Override
public void add(E e) {
throw new UnsupportedOperationException("Add method is not supported in BitListIterator!");
}
}
public ArrayList<E> cloneToArrayList() {
if (rootSet.cardinality() == originList.size() && (CollectionUtils.isEmpty(tailList))) {
return new ArrayList<>(originList);
}
ArrayList<E> arrayList = new ArrayList<>(size());
arrayList.addAll(this);
return arrayList;
}
@Override
public BitList<E> clone() {
return new BitList<>(originList, (BitSet) rootSet.clone(), tailList == null ? null : new LinkedList<>(tailList));
}
}
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