/*
* 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/SpscArrayQueue.java
*/
package rx.internal.util.unsafe;
import static rx.internal.util.unsafe.UnsafeAccess.UNSAFE;
abstract class SpscArrayQueueColdField<E> extends ConcurrentCircularArrayQueue<E> {
private static final Integer MAX_LOOK_AHEAD_STEP = Integer.getInteger("jctools.spsc.max.lookahead.step", 4096);
protected final int lookAheadStep;
public SpscArrayQueueColdField(int capacity) {
super(capacity);
lookAheadStep = Math.min(capacity/4, MAX_LOOK_AHEAD_STEP);
}
}
abstract class SpscArrayQueueL1Pad<E> extends SpscArrayQueueColdField<E> {
long p10, p11, p12, p13, p14, p15, p16;
long p30, p31, p32, p33, p34, p35, p36, p37;
public SpscArrayQueueL1Pad(int capacity) {
super(capacity);
}
}
abstract class SpscArrayQueueProducerFields<E> extends SpscArrayQueueL1Pad<E> {
protected final static long P_INDEX_OFFSET;
static {
try {
P_INDEX_OFFSET =
UNSAFE.objectFieldOffset(SpscArrayQueueProducerFields.class.getDeclaredField("producerIndex"));
} catch (NoSuchFieldException e) {
throw new RuntimeException(e);
}
}
protected long producerIndex;
protected long producerLookAhead;
public SpscArrayQueueProducerFields(int capacity) {
super(capacity);
}
}
abstract class SpscArrayQueueL2Pad<E> extends SpscArrayQueueProducerFields<E> {
long p20, p21, p22, p23, p24, p25, p26;
long p30, p31, p32, p33, p34, p35, p36, p37;
public SpscArrayQueueL2Pad(int capacity) {
super(capacity);
}
}
abstract class SpscArrayQueueConsumerField<E> extends SpscArrayQueueL2Pad<E> {
protected long consumerIndex;
protected final static long C_INDEX_OFFSET;
static {
try {
C_INDEX_OFFSET =
UNSAFE.objectFieldOffset(SpscArrayQueueConsumerField.class.getDeclaredField("consumerIndex"));
} catch (NoSuchFieldException e) {
throw new RuntimeException(e);
}
}
public SpscArrayQueueConsumerField(int capacity) {
super(capacity);
}
}
abstract class SpscArrayQueueL3Pad<E> extends SpscArrayQueueConsumerField<E> {
long p40, p41, p42, p43, p44, p45, p46;
long p30, p31, p32, p33, p34, p35, p36, p37;
public SpscArrayQueueL3Pad(int capacity) {
super(capacity);
}
}
/**
* A Single-Producer-Single-Consumer queue backed by a pre-allocated buffer.
* <p>
* This implementation is a mashup of the <a href="http://sourceforge.net/projects/mc-fastflow/">Fast Flow</a>
* algorithm with an optimization of the offer method taken from the <a
* href="http://staff.ustc.edu.cn/~bhua/publications/IJPP_draft.pdf">BQueue</a> algorithm (a variation on Fast
* Flow), and adjusted to comply with Queue.offer semantics with regards to capacity.<br>
* For convenience the relevant papers are available in the resources folder:<br>
* <i>2010 - Pisa - SPSC Queues on Shared Cache Multi-Core Systems.pdf<br>
* 2012 - Junchang- BQueue- Efficient and Practical Queuing.pdf <br>
* </i> This implementation is wait free.
*
* @author nitsanw
*
* @param <E>
*/
public final class SpscArrayQueue<E> extends SpscArrayQueueL3Pad<E> {
public SpscArrayQueue(final int capacity) {
super(capacity);
}
/**
* {@inheritDoc}
* <p>
* This implementation is correct for single producer thread use only.
*/
@Override
public boolean offer(final E e) {
// local load of field to avoid repeated loads after volatile reads
final E[] lElementBuffer = buffer;
final long index = producerIndex;
final long offset = calcElementOffset(index);
if (null != lvElement(lElementBuffer, offset)){
return false;
}
soProducerIndex(index + 1); // ordered store -> atomic and ordered for size()
soElement(lElementBuffer, offset, e); // StoreStore
return true;
}
/**
* {@inheritDoc}
* <p>
* This implementation is correct for single consumer thread use only.
*/
@Override
public E poll() {
final long index = consumerIndex;
final long offset = calcElementOffset(index);
// local load of field to avoid repeated loads after volatile reads
final E[] lElementBuffer = buffer;
final E e = lvElement(lElementBuffer, offset);// LoadLoad
if (null == e) {
return null;
}
soConsumerIndex(index + 1); // ordered store -> atomic and ordered for size()
soElement(lElementBuffer, offset, null);// StoreStore
return e;
}
/**
* {@inheritDoc}
* <p>
* This implementation is correct for single consumer thread use only.
*/
@Override
public E peek() {
return lvElement(calcElementOffset(consumerIndex));
}
@Override
public int size() {
/*
* It is possible for a thread to be interrupted or reschedule between the read of the producer and consumer
* indices, therefore protection is required to ensure size is within valid range. In the event of concurrent
* polls/offers to this method the size is OVER estimated as we read consumer index BEFORE the producer index.
*/
long after = lvConsumerIndex();
while (true) {
final long before = after;
final long currentProducerIndex = lvProducerIndex();
after = lvConsumerIndex();
if (before == after) {
return (int) (currentProducerIndex - after);
}
}
}
private void soProducerIndex(long v) {
UNSAFE.putOrderedLong(this, P_INDEX_OFFSET, v);
}
private void soConsumerIndex(long v) {
UNSAFE.putOrderedLong(this, C_INDEX_OFFSET, v);
}
private long lvProducerIndex() {
return UNSAFE.getLongVolatile(this, P_INDEX_OFFSET);
}
private long lvConsumerIndex() {
return UNSAFE.getLongVolatile(this, C_INDEX_OFFSET);
}
}