Class SpscArrayQueue<E>
- Type Parameters:
E
- the element type of the queue
- All Implemented Interfaces:
SimplePlainQueue<E>
,SimpleQueue<E>
,Serializable
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:
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Field Summary
FieldsModifier and TypeFieldDescription(package private) final AtomicLong
(package private) final int
(package private) final int
private static final Integer
(package private) final AtomicLong
(package private) long
private static final long
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Constructor Summary
ConstructorsConstructorDescriptionSpscArrayQueue
(int capacity) Constructs an array-backed queue with the given capacity rounded up to the next power of 2 size. -
Method Summary
Modifier and TypeMethodDescription(package private) int
calcElementOffset
(long index) (package private) int
calcElementOffset
(long index, int mask) void
clear()
Removes all enqueued items from this queue.boolean
isEmpty()
Returns true if the queue is empty.(package private) E
lvElement
(int offset) boolean
Atomically enqueue a single value.boolean
Atomically enqueue two values.poll()
Tries to dequeue a value (non-null) or returns null if the queue is empty.(package private) void
soConsumerIndex
(long newIndex) (package private) void
(package private) void
soProducerIndex
(long newIndex) Methods inherited from class java.util.concurrent.atomic.AtomicReferenceArray
accumulateAndGet, compareAndExchange, compareAndExchangeAcquire, compareAndExchangeRelease, compareAndSet, get, getAcquire, getAndAccumulate, getAndSet, getAndUpdate, getOpaque, getPlain, lazySet, length, set, setOpaque, setPlain, setRelease, toString, updateAndGet, weakCompareAndSet, weakCompareAndSetAcquire, weakCompareAndSetPlain, weakCompareAndSetRelease, weakCompareAndSetVolatile
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Field Details
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serialVersionUID
private static final long serialVersionUID- See Also:
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MAX_LOOK_AHEAD_STEP
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mask
final int mask -
producerIndex
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producerLookAhead
long producerLookAhead -
consumerIndex
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lookAheadStep
final int lookAheadStep
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Constructor Details
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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
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Method Details
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offer
Description copied from interface:SimpleQueue
Atomically enqueue a single value.- Specified by:
offer
in interfaceSimpleQueue<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)
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offer
Description copied from interface:SimpleQueue
Atomically enqueue two values.- Specified by:
offer
in interfaceSimpleQueue<E>
- Parameters:
v1
- the first value to enqueue, not nullv2
- 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)
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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 interfaceSimplePlainQueue<E>
- Specified by:
poll
in interfaceSimpleQueue<E>
- Returns:
- the item or null to indicate an empty queue
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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 interfaceSimpleQueue<E>
- Returns:
- true if the queue is empty
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soProducerIndex
void soProducerIndex(long newIndex) -
soConsumerIndex
void soConsumerIndex(long newIndex) -
clear
public void clear()Description copied from interface:SimpleQueue
Removes all enqueued items from this queue.- Specified by:
clear
in interfaceSimpleQueue<E>
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calcElementOffset
int calcElementOffset(long index, int mask) -
calcElementOffset
int calcElementOffset(long index) -
soElement
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lvElement
-