org.jctools.queues.atomic

Class SpscLinkedAtomicQueue<E>

java.lang.Object

java.util.AbstractCollection<E>

java.util.AbstractQueue<E>

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

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

Type Parameters:

E -

All Implemented Interfaces:

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

public final class SpscLinkedAtomicQueue<E>
extends BaseLinkedAtomicQueue<E>

This is a weakened version of the MPSC algorithm as presented on 1024 Cores by D. Vyukov. The original has been adapted to Java and it's quirks with regards to memory model and layout:

1. As this is an SPSC we have no need for XCHG, an ordered store is enough.

The queue is initialized with a stub node which is set to both the producer and consumer node references. From this point follow the notes on offer/poll.

Constructor Summary

Constructors

Constructor and Description
SpscLinkedAtomicQueue()

Method Summary

Modifier and Type	Method and Description
boolean	offer(E e) IMPLEMENTATION NOTES: Offer is allowed from a SINGLE thread. Offer allocates a new node (holding the offered value) and: Sets that node as the producerNode.next Sets the new node as the producerNode From this follows that producerNode.next is always null and for all other nodes node.next is not null.
E	peek()
E	poll() IMPLEMENTATION NOTES: Poll is allowed from a SINGLE thread. Poll reads the next node from the consumerNode and: If it is null, the queue is empty.

Methods inherited from class org.jctools.queues.atomic.BaseLinkedAtomicQueue

getSingleConsumerNodeValue, isEmpty, iterator, lpConsumerNode, lpProducerNode, lvConsumerNode, lvProducerNode, size, spConsumerNode, spProducerNode, xchgProducerNode

Methods inherited from class java.util.AbstractQueue

add, addAll, clear, 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

SpscLinkedAtomicQueue

public SpscLinkedAtomicQueue()

Method Detail

offer

public boolean offer(E e)

IMPLEMENTATION NOTES:
Offer is allowed from a SINGLE thread.
Offer allocates a new node (holding the offered value) and:

1. Sets that node as the producerNode.next
2. Sets the new node as the producerNode

From this follows that producerNode.next is always null and for all other nodes node.next is not null.

See Also:

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

poll

public E poll()

IMPLEMENTATION NOTES:
Poll is allowed from a SINGLE thread.
Poll reads the next node from the consumerNode and:

1. If it is null, the queue is empty.
2. If it is not null set it as the consumer node and return it's now evacuated value.

This means the consumerNode.value is always null, which is also the starting point for the queue. Because null values are not allowed to be offered this is the only node with it's value set to null at any one time.

peek

public E peek()