org.jctools.queues.atomic

Class SpscAtomicArrayQueue<E>

java.lang.Object

java.util.AbstractCollection<E>

java.util.AbstractQueue<E>

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

Type Parameters:

E -

All Implemented Interfaces:

Iterable<E>, Collection<E>, Queue<E>, QueueProgressIndicators

public final class SpscAtomicArrayQueue<E>
extends AbstractQueue<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.

Author:

akarnokd

Field Summary

Fields

Modifier and Type	Field and Description
protected AtomicReferenceArray<E>	buffer
protected int	mask
protected long	producerLookAhead

Constructor Summary

Constructors

Constructor and Description
SpscAtomicArrayQueue(int capacity)

Method Summary

Modifier and Type	Method and Description
protected int	calcElementOffset(long index)
protected int	calcElementOffset(long index, int mask)
void	clear()
long	currentConsumerIndex() This method has no concurrent visibility semantics.
long	currentProducerIndex() This method has no concurrent visibility semantics.
Iterator<E>	iterator()
protected E	lpElement(AtomicReferenceArray<E> buffer, int offset)
protected E	lpElement(int offset)
protected E	lvElement(AtomicReferenceArray<E> buffer, int offset)
protected E	lvElement(int offset)
boolean	offer(E e)
E	peek()
E	poll()
int	size()
protected void	soElement(AtomicReferenceArray<E> buffer, int offset, E value)
protected void	soElement(int offset, E value)
protected void	spElement(AtomicReferenceArray<E> buffer, int offset, E value)
protected void	spElement(int offset, E value)
protected void	svElement(AtomicReferenceArray<E> buffer, int offset, E value)

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

producerLookAhead

protected long producerLookAhead

buffer

protected final AtomicReferenceArray<E> buffer

mask

protected final int mask

Constructor Detail

SpscAtomicArrayQueue

public SpscAtomicArrayQueue(int capacity)

Method Detail

offer

public boolean offer(E e)

Specified by:

offer in interface Queue<E>

poll

public E poll()

Specified by:

poll in interface Queue<E>

peek

public E peek()

Specified by:

peek in interface Queue<E>

size

public int size()

Specified by:

size in interface Collection<E>

Specified by:

size in class 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

iterator

public Iterator<E> iterator()

Specified by:

iterator in interface Iterable<E>

Specified by:

iterator in interface Collection<E>

Specified by:

iterator in class AbstractCollection<E>

clear

public void clear()

Specified by:

clear in interface Collection<E>

Overrides:

clear in class AbstractQueue<E>

calcElementOffset

protected final int calcElementOffset(long index,
                                      int mask)

calcElementOffset

protected final int calcElementOffset(long index)

lvElement

protected final E lvElement(AtomicReferenceArray<E> buffer,
                            int offset)

lpElement

protected final E lpElement(AtomicReferenceArray<E> buffer,
                            int offset)

lpElement

protected final E lpElement(int offset)

spElement

protected final void spElement(AtomicReferenceArray<E> buffer,
                               int offset,
                               E value)

spElement

protected final void spElement(int offset,
                               E value)

soElement

protected final void soElement(AtomicReferenceArray<E> buffer,
                               int offset,
                               E value)

soElement

protected final void soElement(int offset,
                               E value)

svElement

protected final void svElement(AtomicReferenceArray<E> buffer,
                               int offset,
                               E value)

lvElement

protected final E lvElement(int offset)