com.alibaba.nacos.client.naming.utils.Chooser Maven / Gradle / Ivy
/*
* Copyright 1999-2018 Alibaba Group Holding Ltd.
*
* 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.alibaba.nacos.client.naming.utils;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.ThreadLocalRandom;
/**
* Chooser.
*
* @author alibaba
*/
public class Chooser {
private final K uniqueKey;
private volatile Ref ref;
public Chooser(K uniqueKey) {
this(uniqueKey, new ArrayList<>());
}
public Chooser(K uniqueKey, List> pairs) {
Ref ref = new Ref<>(pairs);
ref.refresh();
this.uniqueKey = uniqueKey;
this.ref = ref;
}
/**
* Random get one item.
*
* @return item
*/
public T random() {
List items = ref.items;
if (items.size() == 0) {
return null;
}
if (items.size() == 1) {
return items.get(0);
}
return items.get(ThreadLocalRandom.current().nextInt(items.size()));
}
/**
* Random get one item with weight.
*
* @return item
*/
public T randomWithWeight() {
Ref ref = this.ref;
double random = ThreadLocalRandom.current().nextDouble(0, 1);
int index = Arrays.binarySearch(ref.weights, random);
if (index < 0) {
index = -index - 1;
} else {
return ref.items.get(index);
}
if (index < ref.weights.length) {
if (random < ref.weights[index]) {
return ref.items.get(index);
}
}
if (ref.weights.length == 0) {
throw new IllegalStateException("Cumulative Weight wrong , the array length is equal to 0.");
}
/* This should never happen, but it ensures we will return a correct
* object in case there is some floating point inequality problem
* wrt the cumulative probabilities. */
return ref.items.get(ref.items.size() - 1);
}
public K getUniqueKey() {
return uniqueKey;
}
public Ref getRef() {
return ref;
}
/**
* refresh items.
*
* @param itemsWithWeight items with weight
*/
public void refresh(List> itemsWithWeight) {
Ref newRef = new Ref<>(itemsWithWeight);
newRef.refresh();
newRef.poller = this.ref.poller.refresh(newRef.items);
this.ref = newRef;
}
public class Ref {
private List> itemsWithWeight = new ArrayList<>();
private final List items = new ArrayList<>();
private Poller poller = new GenericPoller<>(items);
private double[] weights;
public Ref(List> itemsWithWeight) {
if (itemsWithWeight != null) {
this.itemsWithWeight = itemsWithWeight;
}
}
/**
* Refresh.
*/
public void refresh() {
double originWeightSum = 0;
int size = 0;
for (Pair item : itemsWithWeight) {
double weight = item.weight();
//ignore item which weight is zero.see test_randomWithWeight_weight0 in ChooserTest
if (weight <= 0) {
continue;
}
items.add(item.item());
if (Double.isInfinite(weight)) {
weight = 10000.0D;
}
if (Double.isNaN(weight)) {
weight = 1.0D;
}
originWeightSum += weight;
size++;
}
weights = new double[size];
double exactWeight;
double randomRange = 0D;
int index = 0;
for (Pair item : itemsWithWeight) {
double singleWeight = item.weight();
//ignore item which weight is zero.see test_randomWithWeight_weight0 in ChooserTest
if (singleWeight <= 0) {
continue;
}
exactWeight = singleWeight / originWeightSum;
weights[index] = randomRange + exactWeight;
randomRange = weights[index++];
}
double doublePrecisionDelta = 0.0001;
if (index == 0 || (Math.abs(weights[index - 1] - 1) < doublePrecisionDelta)) {
return;
}
throw new IllegalStateException(
"Cumulative Weight calculate wrong , the sum of probabilities does not equals 1.");
}
@Override
public int hashCode() {
return itemsWithWeight.hashCode();
}
@SuppressWarnings("unchecked")
@Override
public boolean equals(Object other) {
if (this == other) {
return true;
}
if (other == null) {
return false;
}
if (getClass() != other.getClass()) {
return false;
}
Ref otherRef = (Ref) other;
return this.itemsWithWeight.equals(otherRef.itemsWithWeight);
}
}
@Override
public int hashCode() {
return uniqueKey.hashCode();
}
@Override
public boolean equals(Object other) {
if (this == other) {
return true;
}
if (other == null) {
return false;
}
if (getClass() != other.getClass()) {
return false;
}
Chooser otherChooser = (Chooser) other;
if (this.uniqueKey == null) {
if (otherChooser.getUniqueKey() != null) {
return false;
}
} else {
if (otherChooser.getUniqueKey() == null) {
return false;
} else if (!this.uniqueKey.equals(otherChooser.getUniqueKey())) {
return false;
}
}
return this.ref.equals(otherChooser.getRef());
}
}