org.jctools.queues.atomic

Class MpscAtomicArrayQueue<E>

java.lang.Object

java.util.AbstractCollection<E>

java.util.AbstractQueue<E>

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

Type Parameters:

E -

All Implemented Interfaces:

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

public final class MpscAtomicArrayQueue<E>
extends AbstractQueue<E>
implements QueueProgressIndicators

A Multi-Producer-Single-Consumer queue based on a AtomicReferenceArrayQueue. This implies that any thread may call the offer method, but only a single thread may call poll/peek for correctness to maintained.
This implementation follows patterns documented on the package level for False Sharing protection.
This implementation is using the Fast Flow method for polling from the queue (with minor change to correctly publish the index) and an extension of the Leslie Lamport concurrent queue algorithm (originated by Martin Thompson) on the producer side.

Author:

nitsanw

Field Summary

Fields

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

Constructor Summary

Constructors

Constructor and Description
MpscAtomicArrayQueue(int capacity)

Method Summary

Modifier and Type	Method and Description
protected int	calcElementOffset(long index)
protected int	calcElementOffset(long index, int mask)
protected boolean	casProducerIndex(long expect, long newValue)
void	clear()
long	currentConsumerIndex() This method has no concurrent visibility semantics.
long	currentProducerIndex() This method has no concurrent visibility semantics.
boolean	isEmpty()
Iterator<E>	iterator()
protected E	lpElement(AtomicReferenceArray<E> buffer, int offset)
protected E	lpElement(int offset)
protected long	lvConsumerIndexCache()
protected E	lvElement(AtomicReferenceArray<E> buffer, int offset)
protected E	lvElement(int offset)
boolean	offer(E e) IMPLEMENTATION NOTES: Lock free offer using a single CAS.
E	peek()
E	poll()
int	size()
protected void	soConsumerIndex(long l)
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	svConsumerIndexCache(long v)
protected void	svElement(AtomicReferenceArray<E> buffer, int offset, E value)
int	weakOffer(E e) A wait free alternative to offer which fails on CAS failure.

Methods inherited from class java.util.AbstractQueue

add, addAll, element, remove

Methods inherited from class java.util.AbstractCollection

contains, containsAll, 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, parallelStream, remove, removeAll, removeIf, retainAll, spliterator, stream, toArray, toArray

Methods inherited from interface java.lang.Iterable

forEach

Field Detail

buffer

protected final AtomicReferenceArray<E> buffer

mask

protected final int mask

Constructor Detail

MpscAtomicArrayQueue

public MpscAtomicArrayQueue(int capacity)

Method Detail

offer

public boolean offer(E e)

IMPLEMENTATION NOTES:
Lock free offer using a single CAS. As class name suggests access is permitted to many threads concurrently.

Specified by:

offer in interface Queue<E>

See Also:

Queue.offer(java.lang.Object), MessagePassingQueue.offer(Object)

weakOffer

public final int weakOffer(E e)

A wait free alternative to offer which fails on CAS failure.

Parameters:

e - new element, not null

Returns:

1 if next element cannot be filled, -1 if CAS failed, 0 if successful

poll

public E poll()

IMPLEMENTATION NOTES:
Lock free poll using ordered loads/stores. As class name suggests access is limited to a single thread.

Specified by:

poll in interface Queue<E>

See Also:

Queue.poll(), MessagePassingQueue.poll()

peek

public E peek()

IMPLEMENTATION NOTES:
Lock free peek using ordered loads. As class name suggests access is limited to a single thread.

Specified by:

peek in interface Queue<E>

See Also:

Queue.poll(), MessagePassingQueue.poll()

size

public int size()

Specified by:

size in interface Collection<E>

Specified by:

size in class AbstractCollection<E>

isEmpty

public boolean isEmpty()

Specified by:

isEmpty in interface Collection<E>

Overrides:

isEmpty 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

lvConsumerIndexCache

protected final long lvConsumerIndexCache()

svConsumerIndexCache

protected final void svConsumerIndexCache(long v)

casProducerIndex

protected final boolean casProducerIndex(long expect,
                                         long newValue)

soConsumerIndex

protected void soConsumerIndex(long l)

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)