Package org.jctools.queues

Class ConcurrentCircularArrayQueue<E>

java.lang.Object

java.util.AbstractCollection<E>

java.util.AbstractQueue<E>

org.jctools.queues.ConcurrentCircularArrayQueue<E>

Type Parameters:

E -

All Implemented Interfaces:

IndexedQueueSizeUtil.IndexedQueue, MessagePassingQueue<E>, QueueProgressIndicators

Direct Known Subclasses:

ConcurrentSequencedCircularArrayQueue, MpscArrayQueue, SpmcArrayQueue, SpscArrayQueue

public abstract class ConcurrentCircularArrayQueue<E>
extends java.util.AbstractQueue<E>

Common functionality for array backed queues. The class is pre-padded and the array is padded on either side to help with False Sharing prevention. It is expected that subclasses handle post padding.

Author:

nitsanw

Nested Class Summary

Nested classes/interfaces inherited from interface org.jctools.queues.MessagePassingQueue

MessagePassingQueue.Consumer<T>, MessagePassingQueue.ExitCondition, MessagePassingQueue.Supplier<T>, MessagePassingQueue.WaitStrategy

Field Summary

Fields

Modifier and Type	Field	Description
protected E[]	buffer
protected long	mask

Fields inherited from interface org.jctools.queues.MessagePassingQueue

UNBOUNDED_CAPACITY

Constructor Summary

Constructors

Constructor	Description
ConcurrentCircularArrayQueue(int capacity)

Method Summary

Modifier and Type	Method	Description
protected long	calcElementOffset(long index)
protected static long	calcElementOffset(long index, long mask)
int	capacity()
void	clear()	Removes all items from the queue.
long	currentConsumerIndex()	This method has no concurrent visibility semantics.
long	currentProducerIndex()	This method has no concurrent visibility semantics.
boolean	isEmpty()	This method's accuracy is subject to concurrent modifications happening as the observation is carried out.
java.util.Iterator<E>	iterator()
int	size()	This method's accuracy is subject to concurrent modifications happening as the size is estimated and as such is a best effort rather than absolute value.
java.lang.String	toString()

Methods inherited from class java.util.AbstractCollection

contains, containsAll, remove, removeAll, retainAll, toArray, toArray

Methods inherited from class java.util.AbstractQueue

add, addAll, element, remove

Methods inherited from interface java.util.Collection

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

Methods inherited from interface org.jctools.queues.IndexedQueueSizeUtil.IndexedQueue

lvConsumerIndex, lvProducerIndex

Methods inherited from interface java.lang.Iterable

forEach

Methods inherited from interface org.jctools.queues.MessagePassingQueue

drain, drain, drain, fill, fill, fill, offer, peek, poll, relaxedOffer, relaxedPeek, relaxedPoll

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.Queue

offer, peek, poll

Field Detail

mask

protected final long mask

buffer

protected final E[] buffer

Constructor Detail

ConcurrentCircularArrayQueue

public ConcurrentCircularArrayQueue(int capacity)

Method Detail

calcElementOffset

protected static long calcElementOffset(long index,
                                        long mask)

Parameters:

index - desirable element index

mask - (length - 1)

Returns:

the offset in bytes within the array for a given index.

calcElementOffset

protected final long calcElementOffset(long index)

Parameters:

index - desirable element index

Returns:

the offset in bytes within the array for a given index.

iterator

public java.util.Iterator<E> iterator()

Specified by:

iterator in class java.util.AbstractCollection<E>

size

public final int size()

Description copied from interface: MessagePassingQueue

This method's accuracy is subject to concurrent modifications happening as the size is estimated and as such is a best effort rather than absolute value. For some implementations this method may be O(n) rather than O(1).

Specified by:

size in interface MessagePassingQueue<E>

Specified by:

size in class java.util.AbstractCollection<E>

Returns:

number of messages in the queue, between 0 and Integer.MAX_VALUE but less or equals to capacity (if bounded).

isEmpty

public final boolean isEmpty()

Description copied from interface: MessagePassingQueue

This method's accuracy is subject to concurrent modifications happening as the observation is carried out.

Specified by:

isEmpty in interface MessagePassingQueue<E>

Overrides:

isEmpty in class java.util.AbstractCollection<E>

Returns:

true if empty, false otherwise

toString

public java.lang.String toString()

Overrides:

toString in class java.util.AbstractCollection<E>

clear

public void clear()

Description copied from interface: MessagePassingQueue

Removes all items from the queue. Called from the consumer thread subject to the restrictions appropriate to the implementation and according to the Collection.clear() interface.

Specified by:

clear in interface MessagePassingQueue<E>

Overrides:

clear in class java.util.AbstractQueue<E>

capacity

public int capacity()

Returns:

the capacity of this queue or MessagePassingQueue.UNBOUNDED_CAPACITY if not bounded

currentProducerIndex

public final 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.

Returns:

the current value of the producer progress index

currentConsumerIndex

public final 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.

Returns:

the current value of the consumer progress index