org.agrona.concurrent

Class ManyToOneConcurrentLinkedQueue<E>

java.lang.Object

org.agrona.concurrent.ManyToOneConcurrentLinkedQueue<E>

Type Parameters:

E - element type in the queue.

All Implemented Interfaces:

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

public class ManyToOneConcurrentLinkedQueue<E>
extends Object
implements Queue<E>

Concurrent linked Queue that can be used from many producers and a single consumer.

This is a Java port of Dmitry Vyukov's MPSC linked queue.

Note: This queue breaks the contract for peek and poll in that it can return null when the queue has no item available but size could be greater than zero if an offer is in progress. This is due to the offer being a multi-step process which can start and be interrupted before completion, the thread will later be resumed and the offer process completes. Other methods, such as peek and poll, could spin internally waiting on the offer to complete to provide sequentially consistency across methods but this can have a detrimental effect in a resource starved system. This internal spinning eats up a CPU core and prevents other threads making progress resulting in latency spikes. To avoid this a more relaxed approach is taken in that an in-progress offer is not waited on to complete.

If you wish to check for empty then call isEmpty() rather than size() checking for zero.

Field Summary

Fields

Modifier and Type	Field and Description
protected org.agrona.concurrent.ManyToOneConcurrentLinkedQueuePadding1.Node<E>	head
protected static long	HEAD_OFFSET
protected static long	NEXT_OFFSET
protected org.agrona.concurrent.ManyToOneConcurrentLinkedQueuePadding1.Node<E>	tail
protected static long	TAIL_OFFSET

Constructor Summary

Constructors

Constructor and Description
ManyToOneConcurrentLinkedQueue()

Method Summary

Modifier and Type	Method and Description
boolean	add(E e)
boolean	addAll(Collection<? extends E> c)
void	clear()
boolean	contains(Object o)
boolean	containsAll(Collection<?> c)
E	element()
boolean	isEmpty()
Iterator<E>	iterator()
boolean	offer(E e)
E	peek()
E	poll()
E	remove()
boolean	remove(Object o)
boolean	removeAll(Collection<?> c)
boolean	retainAll(Collection<?> c)
int	size() Size can be considered an approximation on a moving list.
Object[]	toArray()
<T> T[]	toArray(T[] a)
String	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

equals, hashCode, parallelStream, removeIf, spliterator, stream

Methods inherited from interface java.lang.Iterable

forEach

Field Detail

head

protected volatile org.agrona.concurrent.ManyToOneConcurrentLinkedQueuePadding1.Node<E> head

tail

protected volatile org.agrona.concurrent.ManyToOneConcurrentLinkedQueuePadding1.Node<E> tail

HEAD_OFFSET

protected static final long HEAD_OFFSET

TAIL_OFFSET

protected static final long TAIL_OFFSET

NEXT_OFFSET

protected static final long NEXT_OFFSET

Constructor Detail

ManyToOneConcurrentLinkedQueue

public ManyToOneConcurrentLinkedQueue()

Method Detail

add

public boolean add(E e)

Specified by:

add in interface Collection<E>

Specified by:

add in interface Queue<E>

offer

public boolean offer(E e)

Specified by:

offer in interface Queue<E>

remove

public E remove()

Specified by:

remove in interface Queue<E>

poll

public E poll()

Specified by:

poll in interface Queue<E>

element

public E element()

Specified by:

element in interface Queue<E>

peek

public E peek()

Specified by:

peek in interface Queue<E>

size

public int size()

Size can be considered an approximation on a moving list. It is only really stable when the consumer is inactive. If you want to check for queue.size() == 0 then isEmpty() is a better alternative.

This operation is O(n) on the length of the linked chain.

Specified by:

size in interface Collection<E>

Returns:

an approximation for the size of the list.

isEmpty

public boolean isEmpty()

Specified by:

isEmpty in interface Collection<E>

contains

public boolean contains(Object o)

Specified by:

contains in interface Collection<E>

iterator

public Iterator<E> iterator()

Specified by:

iterator in interface Iterable<E>

Specified by:

iterator in interface Collection<E>

toArray

public Object[] toArray()

Specified by:

toArray in interface Collection<E>

toArray

public <T> T[] toArray(T[] a)

Specified by:

toArray in interface Collection<E>

remove

public boolean remove(Object o)

Specified by:

remove in interface Collection<E>

containsAll

public boolean containsAll(Collection<?> c)

Specified by:

containsAll in interface Collection<E>

addAll

public boolean addAll(Collection<? extends E> c)

Specified by:

addAll in interface Collection<E>

removeAll

public boolean removeAll(Collection<?> c)

Specified by:

removeAll in interface Collection<E>

retainAll

public boolean retainAll(Collection<?> c)

Specified by:

retainAll in interface Collection<E>

clear

public void clear()

Specified by:

clear in interface Collection<E>

toString

public String toString()

Overrides:

toString in class Object