/*
* 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 org.jctools.queues;
import org.jctools.util.Pow2;
import org.jctools.util.UnsafeRefArrayAccess;
import static org.jctools.util.UnsafeAccess.UNSAFE;
import static org.jctools.util.UnsafeRefArrayAccess.lvElement;
import static org.jctools.util.UnsafeRefArrayAccess.soElement;
abstract class SpscArrayQueueColdField<E> extends ConcurrentCircularArrayQueue<E> {
public static final int 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 p01, p02, p03, p04, p05, p06, p07;
long p10, p11, p12, p13, p14, p15, p16, p17;
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 producerLimit;
public SpscArrayQueueProducerFields(int capacity) {
super(capacity);
}
}
abstract class SpscArrayQueueL2Pad<E> extends SpscArrayQueueProducerFields<E> {
long p01, p02, p03, p04, p05, p06, p07;
long p10, p11, p12, p13, p14, p15, p16, p17;
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);
}
}
/**
* 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 class SpscArrayQueue<E> extends SpscArrayQueueConsumerField<E> implements QueueProgressIndicators {
long p01, p02, p03, p04, p05, p06, p07;
long p10, p11, p12, p13, p14, p15, p16, p17;
public SpscArrayQueue(final int capacity) {
super(Math.max(Pow2.roundToPowerOfTwo(capacity), 4));
}
/**
* {@inheritDoc}
* <p>
* This implementation is correct for single producer thread use only.
*/
@Override
public boolean offer(final E e) {
if (null == e) {
throw new NullPointerException();
}
// local load of field to avoid repeated loads after volatile reads
final E[] buffer = this.buffer;
final long mask = this.mask;
final long producerIndex = this.producerIndex;
if (producerIndex >= producerLimit &&
!offerSlowPath(buffer, mask, producerIndex)) {
return false;
}
final long offset = calcElementOffset(producerIndex, mask);
soElement(buffer, offset, e); // StoreStore
soProducerIndex(producerIndex + 1); // ordered store -> atomic and ordered for size()
return true;
}
private boolean offerSlowPath(final E[] buffer, final long mask, final long producerIndex) {
final int lookAheadStep = this.lookAheadStep;
if (null == lvElement(buffer, calcElementOffset(producerIndex + lookAheadStep, mask))) {// LoadLoad
producerLimit = producerIndex + lookAheadStep;
}
else{
final long offset = calcElementOffset(producerIndex, mask);
if (null != lvElement(buffer, offset)){
return false;
}
}
return true;
}
/**
* {@inheritDoc}
* <p>
* This implementation is correct for single consumer thread use only.
*/
@Override
public E poll() {
final long consumerIndex = this.consumerIndex;
final long offset = calcElementOffset(consumerIndex);
// local load of field to avoid repeated loads after volatile reads
final E[] buffer = this.buffer;
final E e = lvElement(buffer, offset);// LoadLoad
if (null == e) {
return null;
}
soElement(buffer, offset, null);// StoreStore
soConsumerIndex(consumerIndex + 1); // ordered store -> atomic and ordered for size()
return e;
}
/**
* {@inheritDoc}
* <p>
* This implementation is correct for single consumer thread use only.
*/
@Override
public E peek() {
return UnsafeRefArrayAccess.lvElement(buffer, calcElementOffset(consumerIndex));
}
private void soProducerIndex(long v) {
UNSAFE.putOrderedLong(this, P_INDEX_OFFSET, v);
}
private void soConsumerIndex(long v) {
UNSAFE.putOrderedLong(this, C_INDEX_OFFSET, v);
}
public final long lvProducerIndex() {
return UNSAFE.getLongVolatile(this, P_INDEX_OFFSET);
}
public final long lvConsumerIndex() {
return UNSAFE.getLongVolatile(this, C_INDEX_OFFSET);
}
@Override
public boolean relaxedOffer(final E message) {
return offer(message);
}
@Override
public E relaxedPoll() {
return poll();
}
@Override
public E relaxedPeek() {
return peek();
}
@Override
public int drain(final Consumer<E> c) {
return drain(c, capacity());
}
@Override
public int fill(final Supplier<E> s) {
return fill(s, capacity());
}
@Override
public int drain(final Consumer<E> c, final int limit) {
final E[] buffer = this.buffer;
final long mask = this.mask;
final long consumerIndex = this.consumerIndex;
for (int i = 0; i < limit; i++) {
final long index = consumerIndex + i;
final long offset = calcElementOffset(index, mask);
final E e = lvElement(buffer, offset);// LoadLoad
if (null == e) {
return i;
}
soElement(buffer, offset, null);// StoreStore
soConsumerIndex(index + 1); // ordered store -> atomic and ordered for size()
c.accept(e);
}
return limit;
}
@Override
public int fill(final Supplier<E> s, final int limit) {
final E[] buffer = this.buffer;
final long mask = this.mask;
final int lookAheadStep = this.lookAheadStep;
final long producerIndex = this.producerIndex;
for (int i = 0; i < limit; i++) {
final long index = producerIndex + i;
final long lookAheadElementOffset = calcElementOffset(index + lookAheadStep, mask);
if (null == lvElement(buffer, lookAheadElementOffset)) {// LoadLoad
int lookAheadLimit = Math.min(lookAheadStep, limit - i);
for (int j = 0; j < lookAheadLimit; j++) {
final long offset = calcElementOffset(index + j, mask);
soElement(buffer, offset, s.get()); // StoreStore
soProducerIndex(index + j + 1); // ordered store -> atomic and ordered for size()
}
i += lookAheadLimit - 1;
}
else {
final long offset = calcElementOffset(index, mask);
if (null != lvElement(buffer, offset)){
return i;
}
soElement(buffer, offset, s.get()); // StoreStore
soProducerIndex(index + 1); // ordered store -> atomic and ordered for size()
}
}
return limit;
}
@Override
public void drain(final Consumer<E> c, final WaitStrategy w, final ExitCondition exit) {
final E[] buffer = this.buffer;
final long mask = this.mask;
long consumerIndex = this.consumerIndex;
int counter = 0;
while (exit.keepRunning()) {
for (int i = 0; i < 4096; i++) {
final long offset = calcElementOffset(consumerIndex, mask);
final E e = lvElement(buffer, offset);// LoadLoad
if (null == e) {
counter = w.idle(counter);
continue;
}
consumerIndex++;
counter = 0;
soElement(buffer, offset, null);// StoreStore
soConsumerIndex(consumerIndex); // ordered store -> atomic and ordered for size()
c.accept(e);
}
}
}
@Override
public void fill(final Supplier<E> s, final WaitStrategy w, final ExitCondition e) {
final E[] buffer = this.buffer;
final long mask = this.mask;
final int lookAheadStep = this.lookAheadStep;
long producerIndex = this.producerIndex;
int counter = 0;
while (e.keepRunning()) {
final long lookAheadElementOffset = calcElementOffset(producerIndex + lookAheadStep, mask);
if (null == lvElement(buffer, lookAheadElementOffset)) {// LoadLoad
for (int j = 0; j < lookAheadStep; j++) {
final long offset = calcElementOffset(producerIndex, mask);
producerIndex++;
soElement(buffer, offset, s.get()); // StoreStore
soProducerIndex(producerIndex); // ordered store -> atomic and ordered for size()
}
}
else {
final long offset = calcElementOffset(producerIndex, mask);
if (null != lvElement(buffer, offset)){// LoadLoad
counter = w.idle(counter);
continue;
}
producerIndex++;
counter=0;
soElement(buffer, offset, s.get()); // StoreStore
soProducerIndex(producerIndex); // ordered store -> atomic and ordered for size()
}
}
}
}