io.reactivex.rxjava3.operators

Class SpscArrayQueue<E>

java.lang.Object

java.util.concurrent.atomic.AtomicReferenceArray<E>

io.reactivex.rxjava3.operators.SpscArrayQueue<E>

Type Parameters:

E - the element type of the queue

All Implemented Interfaces:

SimplePlainQueue<E>, SimpleQueue<E>, Serializable

public final class SpscArrayQueue<E>
extends AtomicReferenceArray<E>
implements SimplePlainQueue<E>

A Single-Producer-Single-Consumer queue backed by a pre-allocated buffer.

This implementation is a mashup of the Fast Flow algorithm with an optimization of the offer method taken from the BQueue algorithm (a variation on Fast Flow), and adjusted to comply with Queue.offer semantics with regards to capacity.
For convenience the relevant papers are available in the resources folder:
2010 - Pisa - SPSC Queues on Shared Cache Multi-Core Systems.pdf
2012 - Junchang- BQueue- Efficient and Practical Queuing.pdf
This implementation is wait free.

Since:

3.1.1

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
SpscArrayQueue(int capacity) Constructs an array-backed queue with the given capacity rounded up to the next power of 2 size.

Method Summary

Modifier and Type	Method and Description
void	clear() Removes all enqueued items from this queue.
boolean	isEmpty() Returns true if the queue is empty.
boolean	offer(E e) Atomically enqueue a single value.
boolean	offer(E v1, E v2) Atomically enqueue two values.
E	poll() Tries to dequeue a value (non-null) or returns null if the queue is empty.

Methods inherited from class java.util.concurrent.atomic.AtomicReferenceArray

accumulateAndGet, compareAndSet, get, getAndAccumulate, getAndSet, getAndUpdate, lazySet, length, set, toString, updateAndGet, weakCompareAndSet

Methods inherited from class java.lang.Object

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

Constructor Detail

SpscArrayQueue

public SpscArrayQueue(int capacity)

Constructs an array-backed queue with the given capacity rounded up to the next power of 2 size.

Parameters:

capacity - the maximum number of elements the queue would hold, rounded up to the next power of 2

Method Detail

offer

public boolean offer(E e)

Description copied from interface: SimpleQueue

Atomically enqueue a single value.

Specified by:

offer in interface SimpleQueue<E>

Parameters:

e - the value to enqueue, not null

Returns:

true if successful, false if the value was not enqueued likely due to reaching the queue capacity)

offer

public boolean offer(E v1,
                     E v2)

Description copied from interface: SimpleQueue

Atomically enqueue two values.

Specified by:

offer in interface SimpleQueue<E>

Parameters:

v1 - the first value to enqueue, not null

v2 - the second value to enqueue, not null

Returns:

true if successful, false if the value was not enqueued likely due to reaching the queue capacity)

poll

@Nullable
public E poll()

Description copied from interface: SimpleQueue

Tries to dequeue a value (non-null) or returns null if the queue is empty.

If the producer uses SimpleQueue.offer(Object, Object) and when polling in pairs, if the first poll() returns a non-null item, the second poll() is guaranteed to return a non-null item as well.

Specified by:

poll in interface SimplePlainQueue<E>

Specified by:

poll in interface SimpleQueue<E>

Returns:

the item or null to indicate an empty queue

isEmpty

public boolean isEmpty()

Description copied from interface: SimpleQueue

Returns true if the queue is empty.

Note however that due to potential fused functions in SimpleQueue.poll() it is possible this method returns false but then poll() returns null because the fused function swallowed the available item(s).

Specified by:

isEmpty in interface SimpleQueue<E>

Returns:

true if the queue is empty

clear

public void clear()

Description copied from interface: SimpleQueue

Removes all enqueued items from this queue.

Specified by:

clear in interface SimpleQueue<E>