/*
* Copyright (c) 2011-2017 Pivotal Software Inc, All Rights Reserved.
*
* 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 reactor.util.concurrent;
import java.util.
Collection;
import java.util.
Iterator;
import java.util.
Objects;
import java.util.
Queue;
import java.util.concurrent.atomic.*;
import reactor.util.annotation.
Nullable;
/**
* A bounded, array backed, single-producer single-consumer queue.
*
* This implementation is based on JCTools' SPSC algorithms:
* <a href='https://github.com/JCTools/JCTools/blob/master/jctools-core/src/main/java/org/jctools/queues/SpscArrayQueue.java'>SpscArrayQueue</a>
* and <a href='https://github.com/JCTools/JCTools/blob/master/jctools-core/src/main/java/org/jctools/queues/atomic/SpscAtomicArrayQueue.java'>SpscAtomicArrayQueue</a>
* of which the {@code SpscAtomicArrayQueue} was contributed by one of the authors of this library. The notable difference
* is that this class inlines the AtomicReferenceArray directly and there is no lookahead cache involved;
* item padding has a toll on short lived or bursty uses and lookahead doesn't really matter with small queues.
*
* @param <T> the value type
*/
final class
SpscArrayQueue<T> extends
SpscArrayQueueP3<T> implements
Queue<T> {
/** */
private static final long
serialVersionUID = 494623116936946976L;
SpscArrayQueue(int
capacity) {
super(
Queues.
ceilingNextPowerOfTwo(
capacity));
}
@
Override
public boolean
offer(T
e) {
Objects.
requireNonNull(
e, "e");
long
pi =
producerIndex;
int
offset = (int)
pi &
mask;
if (
get(
offset) != null) {
return false;
}
lazySet(
offset,
e);
PRODUCER_INDEX.
lazySet(this,
pi + 1);
return true;
}
@
Override
@
Nullable
public T
poll() {
long
ci =
consumerIndex;
int
offset = (int)
ci &
mask;
T
v =
get(
offset);
if (
v != null) {
lazySet(
offset, null);
CONSUMER_INDEX.
lazySet(this,
ci + 1);
}
return
v;
}
@
Override
@
Nullable
public T
peek() {
int
offset = (int)
consumerIndex &
mask;
return
get(
offset);
}
@
Override
public boolean
isEmpty() {
return
producerIndex ==
consumerIndex;
}
@
Override
public void
clear() {
while (
poll() != null && !
isEmpty());
}
@
Override
public int
size() {
long
ci =
consumerIndex;
for (;;) {
long
pi =
producerIndex;
long
ci2 =
consumerIndex;
if (
ci ==
ci2) {
return (int)(
pi -
ci);
}
ci =
ci2;
}
}
@
Override
public boolean
contains(
Object o) {
throw new
UnsupportedOperationException();
}
@
Override
public
Iterator<T>
iterator() {
throw new
UnsupportedOperationException();
}
@
Override
public
Object[]
toArray() {
throw new
UnsupportedOperationException();
}
@
Override
public <R> R[]
toArray(R[]
a) {
throw new
UnsupportedOperationException();
}
@
Override
public boolean
remove(
Object o) {
throw new
UnsupportedOperationException();
}
@
Override
public boolean
containsAll(
Collection<?>
c) {
throw new
UnsupportedOperationException();
}
@
Override
public boolean
addAll(
Collection<? extends T>
c) {
throw new
UnsupportedOperationException();
}
@
Override
public boolean
removeAll(
Collection<?>
c) {
throw new
UnsupportedOperationException();
}
@
Override
public boolean
retainAll(
Collection<?>
c) {
throw new
UnsupportedOperationException();
}
@
Override
public boolean
add(T
e) {
throw new
UnsupportedOperationException();
}
@
Override
public T
remove() {
throw new
UnsupportedOperationException();
}
@
Override
public T
element() {
throw new
UnsupportedOperationException();
}
}
class
SpscArrayQueueCold<T> extends
AtomicReferenceArray<T> {
/** */
private static final long
serialVersionUID = 8491797459632447132L;
final int
mask;
public
SpscArrayQueueCold(int
length) {
super(
length);
mask =
length - 1;
}
}
class
SpscArrayQueueP1<T> extends
SpscArrayQueueCold<T> {
/** */
private static final long
serialVersionUID = -4461305682174876914L;
volatile long
p00,
p01,
p02,
p03,
p04,
p05,
p06,
p07;
volatile long
p08,
p09,
p0A,
p0B,
p0C,
p0D,
p0E;
public
SpscArrayQueueP1(int
length) {
super(
length);
}
}
class
SpscArrayQueueProducer<T> extends
SpscArrayQueueP1<T> {
/** */
private static final long
serialVersionUID = 1657408315616277653L;
public
SpscArrayQueueProducer(int
length) {
super(
length);
}
volatile long
producerIndex;
@
SuppressWarnings("rawtypes")
static final
AtomicLongFieldUpdater<
SpscArrayQueueProducer>
PRODUCER_INDEX =
AtomicLongFieldUpdater.
newUpdater(
SpscArrayQueueProducer.class, "producerIndex");
}
class
SpscArrayQueueP2<T> extends
SpscArrayQueueProducer<T> {
/** */
private static final long
serialVersionUID = -5400235061461013116L;
volatile long
p00,
p01,
p02,
p03,
p04,
p05,
p06,
p07;
volatile long
p08,
p09,
p0A,
p0B,
p0C,
p0D,
p0E;
public
SpscArrayQueueP2(int
length) {
super(
length);
}
}
class
SpscArrayQueueConsumer<T> extends
SpscArrayQueueP2<T> {
/** */
private static final long
serialVersionUID = 4075549732218321659L;
public
SpscArrayQueueConsumer(int
length) {
super(
length);
}
volatile long
consumerIndex;
@
SuppressWarnings("rawtypes")
static final
AtomicLongFieldUpdater<
SpscArrayQueueConsumer>
CONSUMER_INDEX =
AtomicLongFieldUpdater.
newUpdater(
SpscArrayQueueConsumer.class, "consumerIndex");
}
class
SpscArrayQueueP3<T> extends
SpscArrayQueueConsumer<T> {
/** */
private static final long
serialVersionUID = -2684922090021364171L;
volatile long
p00,
p01,
p02,
p03,
p04,
p05,
p06,
p07;
volatile long
p08,
p09,
p0A,
p0B,
p0C,
p0D,
p0E;
public
SpscArrayQueueP3(int
length) {
super(
length);
}
}