org.jctools.queues

Class MpscArrayQueue<E>

java.lang.Object

java.util.AbstractCollection<E>

java.util.AbstractQueue<E>

org.jctools.queues.ConcurrentCircularArrayQueue<E>

org.jctools.queues.MpscArrayQueue<E>

Type Parameters:

E -

All Implemented Interfaces:

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

public class MpscArrayQueue<E>
extends ConcurrentCircularArrayQueue<E>
implements QueueProgressIndicators

A Multi-Producer-Single-Consumer queue based on a ConcurrentCircularArrayQueue. 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 inherited from class org.jctools.queues.ConcurrentCircularArrayQueue

buffer, mask, REF_BUFFER_PAD, SPARSE_SHIFT

Constructor Summary

Constructors

Constructor and Description
MpscArrayQueue(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()
protected long	lvConsumerIndex()
protected long	lvConsumerIndexCache()
protected 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.ConcurrentCircularArrayQueue

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

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

Constructor Detail

MpscArrayQueue

public MpscArrayQueue(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

lvConsumerIndex

protected final long lvConsumerIndex()

soConsumerIndex

protected void soConsumerIndex(long l)

lvConsumerIndexCache

protected final long lvConsumerIndexCache()

svConsumerIndexCache

protected final void svConsumerIndexCache(long v)

lvProducerIndex

protected final long lvProducerIndex()

casProducerIndex

protected final boolean casProducerIndex(long expect,
                                         long newValue)