Class MpscLinkedAtomicQueue<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.MpscLinkedAtomicQueue<E>
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- All Implemented Interfaces:
Iterable<E>
,Collection<E>
,Queue<E>
,MessagePassingQueue<E>
public class MpscLinkedAtomicQueue<E> extends AbstractQueue<E>
NOTE: This class was automatically generated by org.jctools.queues.atomic.JavaParsingAtomicLinkedQueueGenerator which can found in the jctools-build module. The original source file is MpscLinkedQueue.java. This is a Java port 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:- Use inheritance to ensure no false sharing occurs between producer/consumer node reference fields.
- Use XCHG functionality to the best of the JDK ability (see differences in JDK7/8 impls).
- Conform to
Queue
contract on poll. The original semantics are available via relaxedPoll.
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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
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Fields inherited from interface org.jctools.queues.MessagePassingQueue
UNBOUNDED_CAPACITY
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Constructor Summary
Constructors Constructor Description MpscLinkedAtomicQueue()
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description int
capacity()
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 wait, 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 wait, MessagePassingQueue.ExitCondition exit)
Stuff the queue with elements from the supplier forever.protected E
getSingleConsumerNodeValue(LinkedQueueAtomicNode<E> currConsumerNode, LinkedQueueAtomicNode<E> nextNode)
boolean
isEmpty()
This method's accuracy is subject to concurrent modifications happening as the observation is carried out.Iterator<E>
iterator()
protected LinkedQueueAtomicNode<E>
newNode()
protected LinkedQueueAtomicNode<E>
newNode(E e)
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 e)
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.boolean
remove(Object o)
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()
protected LinkedQueueAtomicNode<E>
xchgProducerNode(LinkedQueueAtomicNode<E> newValue)
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Methods inherited from class java.util.AbstractCollection
contains, containsAll, 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, removeAll, removeIf, retainAll, spliterator, stream, toArray, toArray, toArray
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Methods inherited from interface org.jctools.queues.MessagePassingQueue
clear
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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.
IMPLEMENTATION NOTES:
Offer is allowed from multiple threads.
Offer allocates a new node and:- Swaps it atomically with current producer node (only one producer 'wins')
- Sets the new node as the node following from the swapped producer node
- Parameters:
e
- notnull
, will throw NPE if it is- Returns:
- true if element was inserted into the queue, false iff full
- See Also:
MessagePassingQueue.offer(Object)
,Queue.offer(java.lang.Object)
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remove
public boolean remove(Object o)
This method is only safe to call from the (single) consumer thread, and is subject to best effort when racing with producers. This method is potentially blocking when "bubble"s in the queue are visible.
- Specified by:
remove
in interfaceCollection<E>
- Overrides:
remove
in classAbstractCollection<E>
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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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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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fill
public void fill(MessagePassingQueue.Supplier<E> s, MessagePassingQueue.WaitStrategy wait, MessagePassingQueue.ExitCondition exit)
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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iterator
public final Iterator<E> iterator()
- Specified by:
iterator
in interfaceCollection<E>
- Specified by:
iterator
in interfaceIterable<E>
- Specified by:
iterator
in classAbstractCollection<E>
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toString
public String toString()
- Overrides:
toString
in classAbstractCollection<E>
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newNode
protected final LinkedQueueAtomicNode<E> newNode()
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newNode
protected final LinkedQueueAtomicNode<E> newNode(E e)
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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).
IMPLEMENTATION NOTES:
This is an O(n) operation as we run through all the nodes and count them.
The accuracy of the value returned by this method is subject to races with producer/consumer threads. In particular when racing with the consumer thread this method may under estimate the size.- 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). - See Also:
Collection.size()
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isEmpty
public boolean isEmpty()
This method's accuracy is subject to concurrent modifications happening as the observation is carried out.
IMPLEMENTATION NOTES:
Queue is empty when producerNode is the same as consumerNode. An alternative implementation would be to observe the producerNode.value is null, which also means an empty queue because only the consumerNode.value is allowed to be null.- Specified by:
isEmpty
in interfaceCollection<E>
- Specified by:
isEmpty
in interfaceMessagePassingQueue<E>
- Overrides:
isEmpty
in classAbstractCollection<E>
- Returns:
- true if empty, false otherwise
- See Also:
MessagePassingQueue.isEmpty()
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getSingleConsumerNodeValue
protected E getSingleConsumerNodeValue(LinkedQueueAtomicNode<E> currConsumerNode, LinkedQueueAtomicNode<E> nextNode)
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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.
IMPLEMENTATION NOTES:
Poll is allowed from a SINGLE thread.
Poll is potentially blocking here as theQueue.poll()
does not allow returningnull
if the queue is not empty. This is very different from the original Vyukov guarantees. SeeMessagePassingQueue.relaxedPoll()
for the original semantics.
Poll readsconsumerNode.next
and:- If it is
null
AND the queue is empty returnnull
, if queue is not empty spin wait for value to become visible. - If it is not
null
set it as the consumer node and return it's now evacuated value.
null
, which is also the starting point for the queue. Becausenull
values are not allowed to be offered this is the only node with it's value set tonull
at any one time.- Returns:
- a message from the queue if one is available,
null
iff empty - See Also:
MessagePassingQueue.poll()
,Queue.poll()
- If it is
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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.
IMPLEMENTATION NOTES:
Peek is allowed from a SINGLE thread.
Peek is potentially blocking here as theQueue.peek()
does not allow returningnull
if the queue is not empty. This is very different from the original Vyukov guarantees. SeeMessagePassingQueue.relaxedPeek()
for the original semantics.
Poll reads the next node from the consumerNode and:- If it is
null
AND the queue is empty returnnull
, if queue is not empty spin wait for value to become visible. - If it is not
null
return it's value.
- Returns:
- a message from the queue if one is available,
null
iff empty - See Also:
MessagePassingQueue.peek()
,Queue.peek()
- If it is
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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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relaxedOffer
public boolean relaxedOffer(E e)
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:
e
- 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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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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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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drain
public void drain(MessagePassingQueue.Consumer<E> c, MessagePassingQueue.WaitStrategy wait, 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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capacity
public int capacity()
- Returns:
- the capacity of this queue or
MessagePassingQueue.UNBOUNDED_CAPACITY
if not bounded
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xchgProducerNode
protected final LinkedQueueAtomicNode<E> xchgProducerNode(LinkedQueueAtomicNode<E> newValue)
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