org.jctools.queues.atomic

Class SpscAtomicArrayQueue<E>

java.lang.Object

java.util.AbstractCollection<E>

java.util.AbstractQueue<E>

org.jctools.queues.atomic.AtomicReferenceArrayQueue<E>

org.jctools.queues.atomic.SpscAtomicArrayQueue<E>

Type Parameters:

E -

All Implemented Interfaces:

java.lang.Iterable<E>, java.util.Collection<E>, java.util.Queue<E>, QueueProgressIndicators

public final class SpscAtomicArrayQueue<E>
extends AtomicReferenceArrayQueue<E>
implements QueueProgressIndicators

A Single-Producer-Single-Consumer queue backed by a pre-allocated buffer.

This implementation is a mashup of the Fast Flow algorithm with an optimization of the offer method taken from the BQueue algorithm (a variation on Fast Flow), and adjusted to comply with Queue.offer semantics with regards to capacity.
For convenience the relevant papers are available in the resources folder:
2010 - Pisa - SPSC Queues on Shared Cache Multi-Core Systems.pdf
2012 - Junchang- BQueue- Efficient and Practical Queuing.pdf
This implementation is wait free.

Field Summary

Fields

Modifier and Type	Field and Description
(package private) java.util.concurrent.atomic.AtomicLong	consumerIndex
(package private) int	lookAheadStep
private static java.lang.Integer	MAX_LOOK_AHEAD_STEP
(package private) java.util.concurrent.atomic.AtomicLong	producerIndex
protected long	producerLookAhead

Fields inherited from class org.jctools.queues.atomic.AtomicReferenceArrayQueue

buffer, mask

Constructor Summary

Constructors

Constructor and Description
SpscAtomicArrayQueue(int capacity)

Method Summary

Modifier and Type	Method and Description
long	currentConsumerIndex() This method has no concurrent visibility semantics.
long	currentProducerIndex() This method has no concurrent visibility semantics.
private long	lvConsumerIndex()
private long	lvProducerIndex()
boolean	offer(E e)
E	peek()
E	poll()
int	size()
private void	soConsumerIndex(long newIndex)
private void	soProducerIndex(long newIndex)

Methods inherited from class org.jctools.queues.atomic.AtomicReferenceArrayQueue

calcElementOffset, calcElementOffset, clear, iterator, lpElement, lpElement, lvElement, lvElement, soElement, soElement, spElement, spElement, svElement

Methods inherited from class java.util.AbstractQueue

add, addAll, element, remove

Methods inherited from class java.util.AbstractCollection

contains, containsAll, isEmpty, remove, removeAll, retainAll, toArray, toArray, toString

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Collection

contains, containsAll, equals, hashCode, isEmpty, parallelStream, remove, removeAll, removeIf, retainAll, spliterator, stream, toArray, toArray

Methods inherited from interface java.lang.Iterable

forEach

Field Detail

MAX_LOOK_AHEAD_STEP

private static final java.lang.Integer MAX_LOOK_AHEAD_STEP

producerIndex

final java.util.concurrent.atomic.AtomicLong producerIndex

producerLookAhead

protected long producerLookAhead

consumerIndex

final java.util.concurrent.atomic.AtomicLong consumerIndex

lookAheadStep

final int lookAheadStep

Constructor Detail

SpscAtomicArrayQueue

public SpscAtomicArrayQueue(int capacity)

Method Detail

offer

public boolean offer(E e)

Specified by:

offer in interface java.util.Queue<E>

poll

public E poll()

Specified by:

poll in interface java.util.Queue<E>

peek

public E peek()

Specified by:

peek in interface java.util.Queue<E>

size

public int size()

Specified by:

size in interface java.util.Collection<E>

Specified by:

size in class java.util.AbstractCollection<E>

currentProducerIndex

public long currentProducerIndex()

Description copied from interface: QueueProgressIndicators

This method has no concurrent visibility semantics. The value returned may be negative. Under normal circumstances 2 consecutive calls to this method can offer an idea of progress made by producer threads by subtracting the 2 results though in extreme cases (if producers have progressed by more than 2^64) this may also fail.
This value will normally indicate number of elements passed into the queue, but may under some circumstances be a derivative of that figure. This method should not be used to derive size or emptiness.

Specified by:

currentProducerIndex in interface QueueProgressIndicators

Returns:

the current value of the producer progress index

currentConsumerIndex

public long currentConsumerIndex()

Description copied from interface: QueueProgressIndicators

This method has no concurrent visibility semantics. The value returned may be negative. Under normal circumstances 2 consecutive calls to this method can offer an idea of progress made by consumer threads by subtracting the 2 results though in extreme cases (if consumers have progressed by more than 2^64) this may also fail.
This value will normally indicate number of elements taken out of the queue, but may under some circumstances be a derivative of that figure. This method should not be used to derive size or emptiness.

Specified by:

currentConsumerIndex in interface QueueProgressIndicators

Returns:

the current value of the consumer progress index

soProducerIndex

private void soProducerIndex(long newIndex)

soConsumerIndex

private void soConsumerIndex(long newIndex)

lvConsumerIndex

private long lvConsumerIndex()

lvProducerIndex

private long lvProducerIndex()