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169 lines (135 loc) · 3.53 KB
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/**
* 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 javaopt.queue;
import java.util.Collection;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Queue;
/**
* <ul>
* <li>Lock free, observing single writer principal.
* </ul>
*/
public final class P1C1QueueStep0<E> implements Queue<E> {
private final E[] buffer;
private volatile long tail = 0;
private volatile long head = 0;
@SuppressWarnings("unchecked")
public P1C1QueueStep0(final int capacity) {
buffer = (E[]) new Object[capacity];
}
public boolean add(final E e) {
if (offer(e)) {
return true;
}
throw new IllegalStateException("Queue is full");
}
public boolean offer(final E e) {
if (null == e) {
throw new NullPointerException("Null is not a valid element");
}
final long currentTail = tail;
final long wrapPoint = currentTail - buffer.length;
if (head <= wrapPoint) {
return false;
}
buffer[(int) (currentTail % buffer.length)] = e;
tail = currentTail + 1;
return true;
}
public E poll() {
final long currentHead = head;
if (currentHead >= tail) {
return null;
}
final int index = (int) (currentHead % buffer.length);
final E e = buffer[index];
buffer[index] = null;
head = currentHead + 1;
return e;
}
public E remove() {
final E e = poll();
if (null == e) {
throw new NoSuchElementException("Queue is empty");
}
return e;
}
public E element() {
final E e = peek();
if (null == e) {
throw new NoSuchElementException("Queue is empty");
}
return e;
}
public E peek() {
return buffer[(int) (head % buffer.length)];
}
public int size() {
return (int) (tail - head);
}
public boolean isEmpty() {
return tail == head;
}
public boolean contains(final Object o) {
if (null == o) {
return false;
}
for (long i = head, limit = tail; i < limit; i++) {
final E e = buffer[(int) (i % buffer.length)];
if (o.equals(e)) {
return true;
}
}
return false;
}
public Iterator<E> iterator() {
throw new UnsupportedOperationException();
}
public Object[] toArray() {
throw new UnsupportedOperationException();
}
public <T> T[] toArray(final T[] a) {
throw new UnsupportedOperationException();
}
public boolean remove(final Object o) {
throw new UnsupportedOperationException();
}
public boolean containsAll(final Collection<?> c) {
for (final Object o : c) {
if (!contains(o)) {
return false;
}
}
return true;
}
public boolean addAll(final Collection<? extends E> c) {
for (final E e : c) {
add(e);
}
return true;
}
public boolean removeAll(final Collection<?> c) {
throw new UnsupportedOperationException();
}
public boolean retainAll(final Collection<?> c) {
throw new UnsupportedOperationException();
}
public void clear() {
Object value;
do {
value = poll();
} while (null != value);
}
}