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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) 2021-2024 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.merkledb.collections;
import edu.umd.cs.findbugs.annotations.NonNull;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Comparator;
import java.util.List;
import java.util.Objects;
import java.util.function.Function;
import java.util.stream.Stream;
/**
* An implementation of ImmutableIndexedObjectList that stores its objects in an on-heap array. The
* position of each object in the array is its self-reported index minus a fixed offset.
*
* This means lookups by self-reported index are extremely fast, but the array may waste some
* space if self-reported indexes are not sequential.
*
* @param the type of the IndexedObject in the list
*/
public class ImmutableIndexedObjectListUsingArray implements ImmutableIndexedObjectList {
/**
* Offset to subtract from self-reported index to get an object's position in the data array (if
* present).
*/
private final int firstIndexOffset;
/**
* Used to create arrays of T.
*/
private final Function arrayProvider;
/**
* The array of data objects, with each object positioned at its self-reported index minus the
* firstIndexOffset.
*/
private final T[] dataArray;
/** Size of this list. Equal to the number of non-null elements in the data array. */
private final int size;
/** Creates a new ImmutableIndexedObjectList from an existing list of objects. */
public ImmutableIndexedObjectListUsingArray(
@NonNull final Function arrProvider, @NonNull final List objects) {
Objects.requireNonNull(arrProvider);
Objects.requireNonNull(objects);
this.arrayProvider = arrProvider;
final List nonNullObjects = new ArrayList<>();
for (final T object : objects) {
if (object != null) {
nonNullObjects.add(object);
}
}
size = nonNullObjects.size();
if (size == 0) {
firstIndexOffset = 0;
dataArray = null;
} else {
// Ensure data is sorted by self-reported index
nonNullObjects.sort(Comparator.comparingInt(IndexedObject::getIndex));
// Determine the first and last indexes
final T firstObject = nonNullObjects.get(0);
firstIndexOffset = firstObject.getIndex();
final int lastIndex = nonNullObjects.get(nonNullObjects.size() - 1).getIndex();
final int range = lastIndex - firstIndexOffset + 1;
// Create a sufficiently large data array and place the nonNullObjects in the correct
// positions
dataArray = arrayProvider.apply(range);
for (final T object : nonNullObjects) {
dataArray[object.getIndex() - firstIndexOffset] = object;
}
}
}
/** {@inheritDoc} */
@Override
public ImmutableIndexedObjectListUsingArray withAddedObject(final T newObject) {
// Ignore null objects
if (newObject == null) {
return this;
}
// Create a temp array list with just non-null objects that belong to the new list
final List newDataArray = new ArrayList<>(Arrays.asList(dataArray));
newDataArray.removeIf(next -> next == null || next.getIndex() == newObject.getIndex());
newDataArray.add(newObject);
return new ImmutableIndexedObjectListUsingArray<>(arrayProvider, newDataArray);
}
/** {@inheritDoc} */
@Override
public ImmutableIndexedObjectListUsingArray withDeletedObjects(@NonNull final Collection objectsToDelete) {
// Share an immutable empty list
if (objectsToDelete.isEmpty() || isEmpty()) {
return this;
}
// Create a temp array list with just non-null objects that belong to the new list
final List newDataArray = new ArrayList<>();
for (final T datum : dataArray) {
if (datum == null) {
continue;
}
if (objectsToDelete.contains(datum)) {
continue;
}
newDataArray.add(datum);
}
return new ImmutableIndexedObjectListUsingArray<>(arrayProvider, newDataArray);
}
/** {@inheritDoc} */
@Override
public T getLast() {
return isEmpty() ? null : dataArray[dataArray.length - 1];
}
/** {@inheritDoc} */
@Override
public T get(final int objectIndex) {
if (objectIndex < 0) {
throw new IndexOutOfBoundsException("Cannot use negative index " + objectIndex);
}
if (isEmpty()) {
return null;
}
final int offsetIndex = objectIndex - firstIndexOffset;
return (offsetIndex < 0 || offsetIndex >= dataArray.length) ? null : dataArray[offsetIndex];
}
/** {@inheritDoc} */
@Override
public Stream stream() {
return Arrays.stream(dataArray).filter(Objects::nonNull);
}
@Override
public String toString() {
return prettyPrintedIndices();
}
private boolean isEmpty() {
/* We null out the data array when constructing from an empty list */
return dataArray == null;
}
/** Get the number of items in this list */
@Override
public int size() {
return size;
}
}