rx.internal.util.atomic.BaseLinkedAtomicQueue Maven / Gradle / Ivy
/*
* 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.
*
* Original License: https://github.com/JCTools/JCTools/blob/master/LICENSE
* Original location: https://github.com/JCTools/JCTools/blob/master/jctools-core/src/main/java/org/jctools/queues/atomic/BaseLinkedAtomicQueue.java
*/
package rx.internal.util.atomic;
import java.util.AbstractQueue;
import java.util.Iterator;
import java.util.concurrent.atomic.AtomicReference;
abstract class BaseLinkedAtomicQueue extends AbstractQueue {
private final AtomicReference> producerNode;
private final AtomicReference> consumerNode;
public BaseLinkedAtomicQueue() {
producerNode = new AtomicReference>();
consumerNode = new AtomicReference>();
}
protected final LinkedQueueNode lvProducerNode() {
return producerNode.get();
}
protected final LinkedQueueNode lpProducerNode() {
return producerNode.get();
}
protected final void spProducerNode(LinkedQueueNode node) {
producerNode.lazySet(node);
}
protected final LinkedQueueNode xchgProducerNode(LinkedQueueNode node) {
return producerNode.getAndSet(node);
}
protected final LinkedQueueNode lvConsumerNode() {
return consumerNode.get();
}
protected final LinkedQueueNode lpConsumerNode() {
return consumerNode.get();
}
protected final void spConsumerNode(LinkedQueueNode node) {
consumerNode.lazySet(node);
}
@Override
public final Iterator iterator() {
throw new UnsupportedOperationException();
}
/**
* {@inheritDoc}
*
* IMPLEMENTATION NOTES:
* This is an O(n) operation as we run through all the nodes and count them.
*
* @see java.util.Queue#size()
*/
@Override
public final int size() {
LinkedQueueNode chaserNode = lvConsumerNode();
final LinkedQueueNode producerNode = lvProducerNode();
int size = 0;
// must chase the nodes all the way to the producer node, but there's no need to chase a moving target.
while (chaserNode != producerNode && size < Integer.MAX_VALUE) {
LinkedQueueNode next;
while ((next = chaserNode.lvNext()) == null) { } // NOPMD
chaserNode = next;
size++;
}
return size;
}
/**
* {@inheritDoc}
*
* IMPLEMENTATION NOTES:
* Queue is empty when producerNode is the same as consumerNode. An alternative implementation would be to observe
* the producerNode.value is null, which also means an empty queue because only the consumerNode.value is allowed to
* be null.
*/
@Override
public final boolean isEmpty() {
return lvConsumerNode() == lvProducerNode();
}
}