io.activej.common.collection.IntrusiveConcurrentStack Maven / Gradle / Ivy
/*
* Copyright (C) 2020 ActiveJ 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 io.activej.common.collection;
import java.util.Iterator;
import java.util.concurrent.atomic.AtomicReference;
/**
* Concurrent implementation of stack data structure (Last In First Out)
*
* @param
*/
public final class IntrusiveConcurrentStack implements Iterable {
public interface Node {
Node getNext();
void setNext(Node next);
}
private final AtomicReference head = new AtomicReference<>();
public void push(E newHead) {
Node oldHead;
do {
oldHead = head.get();
newHead.setNext(oldHead);
} while (!head.compareAndSet(oldHead, newHead));
}
@SuppressWarnings("unchecked")
public E pop() {
Node oldHead;
Node newHead;
do {
oldHead = head.get();
if (oldHead == null) {
return null;
}
newHead = oldHead.getNext();
} while (!head.compareAndSet(oldHead, newHead));
return (E) oldHead;
}
@SuppressWarnings("unchecked")
public E peek() {
Node node = head.get();
return node == null ? null : (E) node;
}
public void clear() {
head.set(null);
}
public boolean isEmpty() {
return peek() == null;
}
public int size() {
int result = 0;
Node node = head.get();
while (node != null) {
node = node.getNext();
result++;
}
return result;
}
@Override
public Iterator iterator() {
return new Iterator() {
Node node = head.get();
@Override
public boolean hasNext() {
return node != null;
}
@SuppressWarnings("unchecked")
@Override
public E next() {
E result = (E) node;
node = node.getNext();
return result;
}
@Override
public void remove() {
throw new UnsupportedOperationException("You can not remove items from concurrent stack");
}
};
}
}