org.jctools.queues.atomic

Class MpscAtomicArrayQueue<E>

java.lang.Object

java.util.AbstractCollection<E>

java.util.AbstractQueue<E>

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

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

Type Parameters:

E -

All Implemented Interfaces:

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

public final class MpscAtomicArrayQueue<E>
extends AtomicReferenceArrayQueue<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.

Field Summary

Fields

Modifier and Type	Field and Description
private java.util.concurrent.atomic.AtomicLong	consumerIndex
private long	headCache
private java.util.concurrent.atomic.AtomicLong	producerIndex

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

buffer, mask

Constructor Summary

Constructors

Constructor and Description
MpscAtomicArrayQueue(int capacity)

Method Summary

Modifier and Type	Method and Description
protected boolean	casProducerIndex(long expect, long newValue)
long	currentConsumerIndex() This method has no concurrent visibility semantics.
long	currentProducerIndex() This method has no concurrent visibility semantics.
boolean	isEmpty()
private long	lvConsumerIndex()
protected long	lvConsumerIndexCache()
private long	lvProducerIndex()
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	svConsumerIndexCache(long v)
int	weakOffer(E e) A wait free alternative to offer which fails on CAS failure.

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, 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

consumerIndex

private final java.util.concurrent.atomic.AtomicLong consumerIndex

producerIndex

private final java.util.concurrent.atomic.AtomicLong producerIndex

headCache

private volatile long headCache

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 java.util.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 java.util.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 java.util.Queue<E>

See Also:

Queue.poll(), MessagePassingQueue.poll()

size

public int size()

Specified by:

size in interface java.util.Collection<E>

Specified by:

size in class java.util.AbstractCollection<E>

isEmpty

public boolean isEmpty()

Specified by:

isEmpty in interface java.util.Collection<E>

Overrides:

isEmpty 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

lvConsumerIndex

private long lvConsumerIndex()

lvProducerIndex

private long lvProducerIndex()

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)