Class SpscAtomicArrayQueue<E>
- java.lang.Object
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- java.util.AbstractCollection<E>
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- java.util.AbstractQueue<E>
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- org.jctools.queues.atomic.SpscAtomicArrayQueue<E>
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- All Implemented Interfaces:
Iterable<E>
,Collection<E>
,Queue<E>
,IndexedQueueSizeUtil.IndexedQueue
,MessagePassingQueue<E>
,QueueProgressIndicators
,SupportsIterator
public class SpscAtomicArrayQueue<E> extends AbstractQueue<E>
NOTE: This class was automatically generated by org.jctools.queues.atomic.JavaParsingAtomicArrayQueueGenerator which can found in the jctools-build module. The original source file is SpscArrayQueue.java. 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.
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Nested Class Summary
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Nested classes/interfaces inherited from interface org.jctools.queues.MessagePassingQueue
MessagePassingQueue.Consumer<T>, MessagePassingQueue.ExitCondition, MessagePassingQueue.Supplier<T>, MessagePassingQueue.WaitStrategy
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Field Summary
Fields Modifier and Type Field Description protected AtomicReferenceArray<E>
buffer
protected int
mask
static int
MAX_LOOK_AHEAD_STEP
protected long
producerLimit
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Fields inherited from interface org.jctools.queues.MessagePassingQueue
UNBOUNDED_CAPACITY
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Constructor Summary
Constructors Constructor Description SpscAtomicArrayQueue(int capacity)
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description int
capacity()
void
clear()
Removes all items from the queue.long
currentConsumerIndex()
This method has no concurrent visibility semantics.long
currentProducerIndex()
This method has no concurrent visibility semantics.int
drain(MessagePassingQueue.Consumer<E> c)
Remove all available item from the queue and hand to consume.int
drain(MessagePassingQueue.Consumer<E> c, int limit)
Remove up to limit elements from the queue and hand to consume.void
drain(MessagePassingQueue.Consumer<E> c, MessagePassingQueue.WaitStrategy w, MessagePassingQueue.ExitCondition exit)
Remove elements from the queue and hand to consume forever.int
fill(MessagePassingQueue.Supplier<E> s)
Stuff the queue with elements from the supplier.int
fill(MessagePassingQueue.Supplier<E> s, int limit)
Stuff the queue with up to limit elements from the supplier.void
fill(MessagePassingQueue.Supplier<E> s, MessagePassingQueue.WaitStrategy w, MessagePassingQueue.ExitCondition e)
Stuff the queue with elements from the supplier forever.boolean
isEmpty()
This method's accuracy is subject to concurrent modifications happening as the observation is carried out.Iterator<E>
iterator()
Get an iterator for this queue.long
lvConsumerIndex()
long
lvProducerIndex()
boolean
offer(E e)
Called from a producer thread subject to the restrictions appropriate to the implementation and according to theQueue.offer(Object)
interface.E
peek()
Called from the consumer thread subject to the restrictions appropriate to the implementation and according to theQueue.peek()
interface.E
poll()
Called from the consumer thread subject to the restrictions appropriate to the implementation and according to theQueue.poll()
interface.boolean
relaxedOffer(E message)
Called from a producer thread subject to the restrictions appropriate to the implementation.E
relaxedPeek()
Called from the consumer thread subject to the restrictions appropriate to the implementation.E
relaxedPoll()
Called from the consumer thread subject to the restrictions appropriate to the implementation.int
size()
This method's accuracy is subject to concurrent modifications happening as the size is estimated and as such is a best effort rather than absolute value.String
toString()
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Methods inherited from class java.util.AbstractQueue
add, addAll, element, remove
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Methods inherited from class java.util.AbstractCollection
contains, containsAll, remove, removeAll, retainAll, toArray, toArray
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Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
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Methods inherited from interface java.util.Collection
contains, containsAll, equals, hashCode, parallelStream, remove, removeAll, removeIf, retainAll, spliterator, stream, toArray, toArray, toArray
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Field Detail
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producerLimit
protected long producerLimit
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MAX_LOOK_AHEAD_STEP
public static final int MAX_LOOK_AHEAD_STEP
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buffer
protected final AtomicReferenceArray<E> buffer
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mask
protected final int mask
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Method Detail
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offer
public boolean offer(E e)
Called from a producer thread subject to the restrictions appropriate to the implementation and according to theQueue.offer(Object)
interface.This implementation is correct for single producer thread use only.
- Parameters:
e
- notnull
, will throw NPE if it is- Returns:
- true if element was inserted into the queue, false iff full
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poll
public E poll()
Called from the consumer thread subject to the restrictions appropriate to the implementation and according to theQueue.poll()
interface.This implementation is correct for single consumer thread use only.
- Returns:
- a message from the queue if one is available,
null
iff empty
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peek
public E peek()
Called from the consumer thread subject to the restrictions appropriate to the implementation and according to theQueue.peek()
interface.This implementation is correct for single consumer thread use only.
- Returns:
- a message from the queue if one is available,
null
iff empty
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relaxedOffer
public boolean relaxedOffer(E message)
Description copied from interface:MessagePassingQueue
Called from a producer thread subject to the restrictions appropriate to the implementation. As opposed toQueue.offer(Object)
this method may return false without the queue being full.- Parameters:
message
- notnull
, will throw NPE if it is- Returns:
- true if element was inserted into the queue, false if unable to offer
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relaxedPoll
public E relaxedPoll()
Description copied from interface:MessagePassingQueue
Called from the consumer thread subject to the restrictions appropriate to the implementation. As opposed toQueue.poll()
this method may returnnull
without the queue being empty.- Returns:
- a message from the queue if one is available,
null
if unable to poll
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relaxedPeek
public E relaxedPeek()
Description copied from interface:MessagePassingQueue
Called from the consumer thread subject to the restrictions appropriate to the implementation. As opposed toQueue.peek()
this method may returnnull
without the queue being empty.- Returns:
- a message from the queue if one is available,
null
if unable to peek
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drain
public int drain(MessagePassingQueue.Consumer<E> c)
Description copied from interface:MessagePassingQueue
Remove all available item from the queue and hand to consume. This should be semantically similar to:M m; while((m = relaxedPoll()) != null){ c.accept(m); }
There's no strong commitment to the queue being empty at the end of a drain. Called from a consumer thread subject to the restrictions appropriate to the implementation.WARNING: Explicit assumptions are made with regards to
MessagePassingQueue.Consumer.accept(T)
make sure you have read and understood these before using this method.- Returns:
- the number of polled elements
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fill
public int fill(MessagePassingQueue.Supplier<E> s)
Description copied from interface:MessagePassingQueue
Stuff the queue with elements from the supplier. Semantically similar to:while(relaxedOffer(s.get());
There's no strong commitment to the queue being full at the end of a fill. Called from a producer thread subject to the restrictions appropriate to the implementation.Unbounded queues will fill up the queue with a fixed amount rather than fill up to oblivion. WARNING: Explicit assumptions are made with regards to
MessagePassingQueue.Supplier.get()
make sure you have read and understood these before using this method.- Returns:
- the number of offered elements
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drain
public int drain(MessagePassingQueue.Consumer<E> c, int limit)
Description copied from interface:MessagePassingQueue
Remove up to limit elements from the queue and hand to consume. This should be semantically similar to:M m; int i = 0; for(;i < limit && (m = relaxedPoll()) != null; i++){ c.accept(m); } return i;
There's no strong commitment to the queue being empty at the end of a drain. Called from a consumer thread subject to the restrictions appropriate to the implementation.
WARNING: Explicit assumptions are made with regards to
MessagePassingQueue.Consumer.accept(T)
make sure you have read and understood these before using this method.- Returns:
- the number of polled elements
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fill
public int fill(MessagePassingQueue.Supplier<E> s, int limit)
Description copied from interface:MessagePassingQueue
Stuff the queue with up to limit elements from the supplier. Semantically similar to:for(int i=0; i < limit && relaxedOffer(s.get()); i++);
There's no strong commitment to the queue being full at the end of a fill. Called from a producer thread subject to the restrictions appropriate to the implementation. WARNING: Explicit assumptions are made with regards to
MessagePassingQueue.Supplier.get()
make sure you have read and understood these before using this method.- Returns:
- the number of offered elements
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drain
public void drain(MessagePassingQueue.Consumer<E> c, MessagePassingQueue.WaitStrategy w, MessagePassingQueue.ExitCondition exit)
Description copied from interface:MessagePassingQueue
Remove elements from the queue and hand to consume forever. Semantically similar to:int idleCounter = 0; while (exit.keepRunning()) { E e = relaxedPoll(); if(e==null){ idleCounter = wait.idle(idleCounter); continue; } idleCounter = 0; c.accept(e); }
Called from a consumer thread subject to the restrictions appropriate to the implementation.
WARNING: Explicit assumptions are made with regards to
MessagePassingQueue.Consumer.accept(T)
make sure you have read and understood these before using this method.
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fill
public void fill(MessagePassingQueue.Supplier<E> s, MessagePassingQueue.WaitStrategy w, MessagePassingQueue.ExitCondition e)
Description copied from interface:MessagePassingQueue
Stuff the queue with elements from the supplier forever. Semantically similar to:int idleCounter = 0; while (exit.keepRunning()) { E e = s.get(); while (!relaxedOffer(e)) { idleCounter = wait.idle(idleCounter); continue; } idleCounter = 0; }
Called from a producer thread subject to the restrictions appropriate to the implementation. The main difference being that implementors MUST assure room in the queue is available BEFORE calling
MessagePassingQueue.Supplier.get()
. WARNING: Explicit assumptions are made with regards toMessagePassingQueue.Supplier.get()
make sure you have read and understood these before using this method.
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lvConsumerIndex
public final long lvConsumerIndex()
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lvProducerIndex
public final long lvProducerIndex()
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toString
public String toString()
- Overrides:
toString
in classAbstractCollection<E>
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clear
public void clear()
Description copied from interface:MessagePassingQueue
Removes all items from the queue. Called from the consumer thread subject to the restrictions appropriate to the implementation and according to theCollection.clear()
interface.- Specified by:
clear
in interfaceCollection<E>
- Specified by:
clear
in interfaceMessagePassingQueue<E>
- Overrides:
clear
in classAbstractQueue<E>
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capacity
public final int capacity()
- Specified by:
capacity
in interfaceIndexedQueueSizeUtil.IndexedQueue
- Specified by:
capacity
in interfaceMessagePassingQueue<E>
- Returns:
- the capacity of this queue or
MessagePassingQueue.UNBOUNDED_CAPACITY
if not bounded
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size
public final int size()
This method's accuracy is subject to concurrent modifications happening as the size is estimated and as such is a best effort rather than absolute value. For some implementations this method may be O(n) rather than O(1).- Specified by:
size
in interfaceCollection<E>
- Specified by:
size
in interfaceMessagePassingQueue<E>
- Specified by:
size
in classAbstractCollection<E>
- Returns:
- number of messages in the queue, between 0 and
Integer.MAX_VALUE
but less or equals to capacity (if bounded).
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isEmpty
public final boolean isEmpty()
Description copied from interface:MessagePassingQueue
This method's accuracy is subject to concurrent modifications happening as the observation is carried out.- Specified by:
isEmpty
in interfaceCollection<E>
- Specified by:
isEmpty
in interfaceMessagePassingQueue<E>
- Overrides:
isEmpty
in classAbstractCollection<E>
- Returns:
- true if empty, false otherwise
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currentProducerIndex
public final long currentProducerIndex()
Description copied from interface:QueueProgressIndicators
This method has no concurrent visibility semantics. The value returned may be negative. Under normal circumstances 2 consecutive calls to this method can offer an idea of progress made by producer threads by subtracting the 2 results though in extreme cases (if producers have progressed by more than 2^64) this may also fail.
This value will normally indicate number of elements passed into the queue, but may under some circumstances be a derivative of that figure. This method should not be used to derive size or emptiness.- Specified by:
currentProducerIndex
in interfaceQueueProgressIndicators
- Returns:
- the current value of the producer progress index
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currentConsumerIndex
public final long currentConsumerIndex()
Description copied from interface:QueueProgressIndicators
This method has no concurrent visibility semantics. The value returned may be negative. Under normal circumstances 2 consecutive calls to this method can offer an idea of progress made by consumer threads by subtracting the 2 results though in extreme cases (if consumers have progressed by more than 2^64) this may also fail.
This value will normally indicate number of elements taken out of the queue, but may under some circumstances be a derivative of that figure. This method should not be used to derive size or emptiness.- Specified by:
currentConsumerIndex
in interfaceQueueProgressIndicators
- Returns:
- the current value of the consumer progress index
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iterator
public final Iterator<E> iterator()
Get an iterator for this queue. This method is thread safe.The iterator provides a best-effort snapshot of the elements in the queue. The returned iterator is not guaranteed to return elements in queue order, and races with the consumer thread may cause gaps in the sequence of returned elements. Like {link #relaxedPoll}, the iterator may not immediately return newly inserted elements.
- Specified by:
iterator
in interfaceCollection<E>
- Specified by:
iterator
in interfaceIterable<E>
- Specified by:
iterator
in classAbstractCollection<E>
- Returns:
- The iterator.
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