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/*
* Copyright 2017, OpenCensus Authors
*
* 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 io.opencensus.implcore.trace.internal;
import static com.google.common.base.Preconditions.checkArgument;
import io.opencensus.implcore.internal.CheckerFrameworkUtils;
import io.opencensus.implcore.trace.internal.ConcurrentIntrusiveList.Element;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import javax.annotation.Nullable;
import javax.annotation.concurrent.ThreadSafe;
/**
* An {@code ConcurrentIntrusiveList<T>} is a doubly-linked list where the link pointers are
* embedded in the elements. This makes insertion and removal into a known position constant time.
*
* <p>Elements must derive from the {@code Element<T extends Element<T>>} interface:
*
* <pre><code>
* class MyClass implements {@code Element<MyClass>} {
* private MyClass next = null;
* private MyClass prev = null;
*
* {@literal @}Override
* MyClass getNext() {
* return next;
* }
*
* {@literal @}Override
* void setNext(MyClass element) {
* next = element;
* }
*
* {@literal @}Override
* MyClass getPrev() {
* return prev;
* }
*
* {@literal @}Override
* void setPrev(MyClass element) {
* prev = element;
* }
* }
* </code></pre>
*/
@ThreadSafe
public final class ConcurrentIntrusiveList<T extends Element<T>> {
private int size = 0;
@Nullable private T head = null;
public ConcurrentIntrusiveList() {}
/**
* Adds the given {@code element} to the list.
*
* @param element the element to add.
* @throws IllegalArgumentException if the element is already in a list.
*/
public synchronized void addElement(T element) {
checkArgument(
element.getNext() == null && element.getPrev() == null && element != head,
"Element already in a list.");
size++;
if (head == null) {
head = element;
} else {
head.setPrev(element);
element.setNext(head);
head = element;
}
}
/**
* Removes the given {@code element} from the list.
*
* @param element the element to remove.
* @throws IllegalArgumentException if the element is not in the list.
*/
public synchronized void removeElement(T element) {
checkArgument(
element.getNext() != null || element.getPrev() != null || element == head,
"Element not in the list.");
size--;
if (element.getPrev() == null) {
// This is the first element
head = element.getNext();
if (head != null) {
// If more than one element in the list.
head.setPrev(null);
element.setNext(null);
}
} else if (element.getNext() == null) {
// This is the last element, and there is at least another element because
// element.getPrev() != null.
CheckerFrameworkUtils.castNonNull(element.getPrev()).setNext(null);
element.setPrev(null);
} else {
CheckerFrameworkUtils.castNonNull(element.getPrev()).setNext(element.getNext());
CheckerFrameworkUtils.castNonNull(element.getNext()).setPrev(element.getPrev());
element.setNext(null);
element.setPrev(null);
}
}
/**
* Returns the number of elements in this list.
*
* @return the number of elements in this list.
*/
public synchronized int size() {
return size;
}
/**
* Returns all the elements from this list.
*
* @return all the elements from this list.
*/
public synchronized Collection<T> getAll() {
List<T> all = new ArrayList<T>(size);
for (T e = head; e != null; e = e.getNext()) {
all.add(e);
}
return all;
}
/**
* This is an interface that must be implemented by any element that uses {@link
* ConcurrentIntrusiveList}.
*
* @param <T> the element that will be used for the list.
*/
public interface Element<T extends Element<T>> {
/**
* Returns a reference to the next element in the list.
*
* @return a reference to the next element in the list.
*/
@Nullable
T getNext();
/**
* Sets the reference to the next element in the list.
*
* @param element the reference to the next element in the list.
*/
void setNext(@Nullable T element);
/**
* Returns a reference to the previous element in the list.
*
* @return a reference to the previous element in the list.
*/
@Nullable
T getPrev();
/**
* Sets the reference to the previous element in the list.
*
* @param element the reference to the previous element in the list.
*/
void setPrev(@Nullable T element);
}
}
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