com.zaxxer.influx4j.util

Class FAAArrayQueue<E>

java.lang.Object

com.zaxxer.influx4j.util.FAAArrayQueue<E>

public class FAAArrayQueue<E>
extends Object

Fetch-And-Add Array Queue

Each node has one array but we don't search for a vacant entry. Instead, we use FAA to obtain an index in the array, for enqueueing or dequeuing. There are some similarities between this queue and the basic queue in YMC: http://chaoran.me/assets/pdf/wfq-ppopp16.pdf but it's not the same because the queue in listing 1 is obstruction-free, while our algorithm is lock-free. In FAAArrayQueue eventually a new node will be inserted (using Michael-Scott's algorithm) and it will have an item pre-filled in the first position, which means that at most, after BUFFER_SIZE steps, one item will be enqueued (and it can then be dequeued). This kind of progress is lock-free. Each entry in the array may contain one of three possible values: - A valid item that has been enqueued; - nullptr, which means no item has yet been enqueued in that position; - taken, a special value that means there was an item but it has been dequeued; Enqueue algorithm: FAA + CAS(null,item) Dequeue algorithm: FAA + CAS(item,taken) Consistency: Linearizable enqueue() progress: lock-free dequeue() progress: lock-free Memory Reclamation: Hazard Pointers (lock-free) Uncontended enqueue: 1 FAA + 1 CAS + 1 HP Uncontended dequeue: 1 FAA + 1 CAS + 1 HP

Lock-Free Linked List as described in Maged Michael and Michael Scott's paper:
Simple, Fast, and Practical Non-Blocking and Blocking Concurrent Queue Algorithms The paper on Hazard Pointers is named "Hazard Pointers: Safe Memory Reclamation for Lock-Free objects" and it is available here:
Hazard Pointers: Safe Memory Reclamation for Lock-Free objects

Author:

Pedro Ramalhete, Andreia Correia

Constructor Summary

Constructors

Constructor and Description
FAAArrayQueue()

Method Summary

Modifier and Type	Method and Description
E	dequeue() Progress condition: lock-free
void	enqueue(E item) Progress Condition: Lock-Free
int	size() Get the current size of the queue.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

FAAArrayQueue

public FAAArrayQueue()

Method Detail

enqueue

public void enqueue(E item)

Progress Condition: Lock-Free

Parameters:

item - must not be null

dequeue

public E dequeue()

Progress condition: lock-free

Returns:

a dequeued item, or null

size

public int size()

Get the current size of the queue. This size is temporal and subject to race conditions.

Returns:

the number of items in the queue at the time of invocation