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Swirlds is a software platform designed to build fully-distributed applications that harness the power of the cloud without servers. Now you can develop applications with fairness in decision making, speed, trust and reliability, at a fraction of the cost of traditional server-based platforms.
/*
* Copyright (C) 2021-2023 Hedera Hashgraph, LLC
*
* 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.swirlds.common.test.set;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.Random;
import java.util.Set;
/**
* Similar to a {@link RandomAccessHashSet} but with hotspots (i.e. elements that are chosen more oftan than others).
*
* @param
* the type of the object held by the set
*/
public class HotspotHashSet implements RandomAccessSet {
private final List hotspots;
private final List> sets;
private final double totalWeight;
private int totalCount;
private static final int DEFAULT_SET_INDEX = 0;
/**
* Create a new random access set that has a number of hotspots.
*
* @param defaultWeight
* the weight that determines the frequency that elements that are not in a hotspot are returned
* If the set contains 1,000 elements and has a single hotspot with 100 elements then 900 elements
* will be in the default set. If the default weight is 1.0 and a hotspot of 2.0, then elements
* from the hotspot will be returned twice as often as elements in the default set.
* @param hotspots
* an array of zero or more hotspot configurations
*/
public HotspotHashSet(final double defaultWeight, final Hotspot... hotspots) {
final int hotspotCount = (hotspots == null ? 0 : hotspots.length) + 1;
this.hotspots = new ArrayList<>(hotspotCount);
sets = new ArrayList<>(hotspotCount);
// Create default set
this.hotspots.add(new Hotspot(defaultWeight, Integer.MAX_VALUE));
sets.add(new RandomAccessHashSet<>());
double weightSum = defaultWeight;
if (hotspots != null) {
for (final Hotspot hotspot : hotspots) {
this.hotspots.add(hotspot);
weightSum += hotspot.getWeight();
sets.add(new RandomAccessHashSet<>());
}
}
totalWeight = weightSum;
}
/**
* Choose a random set of entries based on hotspot weight.
*
* @return the index of the chosen set
*/
private int chooseSetIndexByWeight(final Random random) {
double choice = random.nextDouble() * totalWeight;
for (int index = 0; index < sets.size(); index++) {
choice -= hotspots.get(index).getWeight();
if (choice < 0) {
return index;
}
}
// If rounding error causes us to not choose a set
// (exceptionally unlikely, if not impossible) then just return default.
return DEFAULT_SET_INDEX;
}
/**
* Choose a random set of entries where the weight is equal to the size of the set.
*
* @return the index of the chosen set
*/
private int chooseSetIndexBySize(final Random random) {
double choice = random.nextDouble() * totalCount;
for (int index = 0; index < sets.size(); index++) {
choice -= sets.get(index).size();
if (choice < 0) {
return index;
}
}
// If rounding error causes us to not choose a set
// (exceptionally unlikely, if not impossible) then just return default.
return DEFAULT_SET_INDEX;
}
/**
* Get a random element, taking hotspots into account.
*
* @param random
* a source of randomness
* @return an element chosen randomly
* @throws NoSuchElementException
* if the set is empty
*/
public T getWeighted(final Random random) {
if (totalCount == 0) {
throw new NoSuchElementException("set is empty, can not get element");
}
while (true) {
final int setIndex = chooseSetIndexByWeight(random);
final RandomAccessHashSet set = sets.get(setIndex);
if (setIndex == DEFAULT_SET_INDEX) {
if (set.size() > 0) {
return set.get(random);
}
} else {
final Hotspot hotspot = hotspots.get(setIndex);
if (hotspot.getHotspotSize() > set.size()) {
// Attempt to pull new element into this set
final RandomAccessHashSet defaultSet = sets.get(DEFAULT_SET_INDEX);
if (defaultSet.size() > 0) {
final T element = defaultSet.get(random);
defaultSet.remove(element);
set.add(element);
return element;
}
} else {
return set.get(random);
}
}
}
}
/**
* {@inheritDoc}
*/
@Override
public T get(final Random random) {
if (totalCount == 0) {
throw new NoSuchElementException("set is empty, can not get element");
}
final int setIndex = chooseSetIndexBySize(random);
final RandomAccessHashSet set = sets.get(setIndex);
return set.get(random);
}
/**
* {@inheritDoc}
*/
@Override
public T get(final int index) {
if (index >= totalCount || index < 0) {
throw new IndexOutOfBoundsException("requested index " + index + " is invalid");
}
int count = 0;
for (final RandomAccessHashSet set : sets) {
if (count + set.size() > index) {
return set.get(index - count);
}
count += set.size();
}
throw new IllegalStateException("unable to find element at index " + index);
}
/**
* Get a set containing all elements in a given hotspot.
*
* @param index
* the index of the hotspot
* @return a set containing the hotspot elements
*/
public RandomAccessHashSet getHotspotSet(final int index) {
return sets.get(index);
}
/**
* Get the total number of hotspots.
*/
public int getHotspotCount() {
return sets.size();
}
/**
* {@inheritDoc}
*/
@Override
public int size() {
return totalCount;
}
/**
* {@inheritDoc}
*/
@Override
public boolean isEmpty() {
return totalCount == 0;
}
/**
* {@inheritDoc}
*/
@Override
public boolean contains(final Object o) {
for (final Set set : sets) {
if (set.contains(o)) {
return true;
}
}
return false;
}
/**
* {@inheritDoc}
*/
@Override
public Iterator iterator() {
return new HotspotSetIterator<>(sets);
}
/**
* Add all elements in a set to an array at the given position.
*/
private void addSetToArray(final Object[] array, final int startIndex, final RandomAccessHashSet set) {
for (int index = 0; index < set.size(); index++) {
array[index + startIndex] = set.get(index);
}
}
/**
* {@inheritDoc}
*/
@Override
public Object[] toArray() {
final Object[] array = new Object[totalCount];
int index = 0;
for (final RandomAccessHashSet set : sets) {
addSetToArray(array, index, set);
index += set.size();
}
return array;
}
/**
* Unsupported.
*
* @throws UnsupportedOperationException
* if this method is called
*/
@Override
public T1[] toArray(final T1[] a) {
throw new UnsupportedOperationException();
}
/**
* {@inheritDoc}
*/
@Override
public boolean add(final T t) {
final boolean added = sets.get(DEFAULT_SET_INDEX).add(t);
if (added) {
totalCount++;
}
return added;
}
/**
* {@inheritDoc}
*/
@Override
public boolean remove(final Object o) {
for (final Set set : sets) {
if (set.remove(o)) {
totalCount--;
return true;
}
}
return false;
}
/**
* {@inheritDoc}
*/
@Override
public boolean containsAll(final Collection c) {
for (final Object o : c) {
if (!contains(o)) {
return false;
}
}
return true;
}
/**
* {@inheritDoc}
*/
@Override
public void clear() {
for (final Set set : sets) {
set.clear();
}
totalCount = 0;
}
}