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/*
* Licensed to Elasticsearch under one or more contributor
* license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright
* ownership. Elasticsearch 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.elasticsearch.common.util.concurrent;
import org.elasticsearch.ElasticsearchGenerationException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.atomic.AtomicReferenceArray;
/**
* A list backed by an {@link AtomicReferenceArray} with potential null values, easily allowing
* to get the concrete values as a list using {@link #asList()}.
*/
public class AtomicArray<E> {
private final AtomicReferenceArray<E> array;
private volatile List<E> nonNullList;
public AtomicArray(int size) {
array = new AtomicReferenceArray<>(size);
}
/**
* The size of the expected results, including potential null values.
*/
public int length() {
return array.length();
}
/**
* Sets the element at position {@code i} to the given value.
*
* @param i the index
* @param value the new value
*/
public void set(int i, E value) {
array.set(i, value);
if (nonNullList != null) { // read first, lighter, and most times it will be null...
nonNullList = null;
}
}
public final void setOnce(int i, E value) {
if (array.compareAndSet(i, null, value) == false) {
throw new IllegalStateException("index [" + i + "] has already been set");
}
if (nonNullList != null) { // read first, lighter, and most times it will be null...
nonNullList = null;
}
}
/**
* Gets the current value at position {@code i}.
*
* @param i the index
* @return the current value
*/
public E get(int i) {
return array.get(i);
}
/**
* Returns the it as a non null list.
*/
public List<E> asList() {
if (nonNullList == null) {
if (array == null || array.length() == 0) {
nonNullList = Collections.emptyList();
} else {
List<E> list = new ArrayList<>(array.length());
for (int i = 0; i < array.length(); i++) {
E e = array.get(i);
if (e != null) {
list.add(e);
}
}
nonNullList = list;
}
}
return nonNullList;
}
/**
* Copies the content of the underlying atomic array to a normal one.
*/
public E[] toArray(E[] a) {
if (a.length != array.length()) {
throw new ElasticsearchGenerationException("AtomicArrays can only be copied to arrays of the same size");
}
for (int i = 0; i < array.length(); i++) {
a[i] = array.get(i);
}
return a;
}
}
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