Class MpmcAtomicArrayQueue<E>
- All Implemented Interfaces:
Iterable<E>
,Collection<E>
,Queue<E>
,IndexedQueueSizeUtil.IndexedQueue
,MessagePassingQueue<E>
,QueueProgressIndicators
,SupportsIterator
ConcurrentCircularArrayQueue<E>
. This
implies that any and all threads may call the offer/poll/peek methods and correctness is maintained. This implementation follows patterns documented on the package level for False Sharing protection.
The algorithm for offer/poll is an adaptation of the one put forward by D. Vyukov (See here). The original algorithm uses an array of structs which should offer nice locality properties but is sadly not possible in Java (waiting on Value Types or similar). The alternative explored here utilizes 2 arrays, one for each field of the struct. There is a further alternative in the experimental project which uses iteration phase markers to achieve the same algo and is closer structurally to the original, but sadly does not perform as well as this implementation.
Tradeoffs to keep in mind:
- Padding for false sharing: counter fields and queue fields are all padded as well as either side of both arrays. We are trading memory to avoid false sharing(active and passive).
- 2 arrays instead of one: The algorithm requires an extra array of longs matching the size of the elements array. This is doubling/tripling the memory allocated for the buffer.
- Power of 2 capacity: Actual elements buffer (and sequence buffer) is the closest power of 2 larger or equal to the requested capacity.
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Nested Class Summary
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
FieldsModifier and TypeFieldDescriptionprivate final int
static final int
Fields inherited from class org.jctools.queues.atomic.MpmcAtomicArrayQueueL3Pad
b000, b001, b002, b003, b004, b005, b006, b007, b010, b011, b012, b013, b014, b015, b016, b017, b020, b021, b022, b023, b024, b025, b026, b027, b030, b031, b032, b033, b034, b035, b036, b037, b040, b041, b042, b043, b044, b045, b046, b047, b050, b051, b052, b053, b054, b055, b056, b057, b060, b061, b062, b063, b064, b065, b066, b067, b070, b071, b072, b073, b074, b075, b076, b077, b100, b101, b102, b103, b104, b105, b106, b107, b110, b111, b112, b113, b114, b115, b116, b117, b120, b121, b122, b123, b124, b125, b126, b127, b130, b131, b132, b133, b134, b135, b136, b137, b140, b141, b142, b143, b144, b145, b146, b147, b150, b151, b152, b153, b154, b155, b156, b157, b160, b161, b162, b163, b164, b165, b166, b167, b170, b171, b172, b173, b174, b175, b176, b177
Fields inherited from class org.jctools.queues.atomic.SequencedAtomicReferenceArrayQueue
sequenceBuffer
Fields inherited from class org.jctools.queues.atomic.AtomicReferenceArrayQueue
buffer, mask
Fields inherited from interface org.jctools.queues.MessagePassingQueue
UNBOUNDED_CAPACITY
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionint
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.private int
drainOneByOne
(MessagePassingQueue.Consumer<E> c, int limit) int
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.private int
fillOneByOne
(MessagePassingQueue.Supplier<E> s, int limit) private boolean
notAvailable
(long index, int mask, AtomicLongArray sBuffer, long expectedSeq) boolean
Called from a producer thread subject to the restrictions appropriate to the implementation and according to theQueue.offer(Object)
interface.peek()
Called from the consumer thread subject to the restrictions appropriate to the implementation and according to theQueue.peek()
interface.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.Called from the consumer thread subject to the restrictions appropriate to the implementation.Called from the consumer thread subject to the restrictions appropriate to the implementation.Methods inherited from class org.jctools.queues.atomic.MpmcAtomicArrayQueueConsumerIndexField
casConsumerIndex, lvConsumerIndex
Methods inherited from class org.jctools.queues.atomic.MpmcAtomicArrayQueueProducerIndexField
casProducerIndex, lvProducerIndex
Methods inherited from class org.jctools.queues.atomic.SequencedAtomicReferenceArrayQueue
calcSequenceOffset, calcSequenceOffset, lvSequence, soSequence
Methods inherited from class org.jctools.queues.atomic.AtomicReferenceArrayQueue
capacity, clear, currentConsumerIndex, currentProducerIndex, isEmpty, iterator, size, toString
Methods inherited from class java.util.AbstractQueue
add, addAll, element, remove
Methods inherited from class java.util.AbstractCollection
contains, containsAll, remove, removeAll, retainAll, toArray, toArray
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
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 Details
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MAX_LOOK_AHEAD_STEP
public static final int MAX_LOOK_AHEAD_STEP -
lookAheadStep
private final int lookAheadStep
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Constructor Details
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MpmcAtomicArrayQueue
public MpmcAtomicArrayQueue(int capacity)
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Method Details
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offer
Description copied from interface:MessagePassingQueue
Called from a producer thread subject to the restrictions appropriate to the implementation and according to theQueue.offer(Object)
interface.- 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
Called from the consumer thread subject to the restrictions appropriate to the implementation and according to theQueue.poll()
interface.Because return null indicates queue is empty we cannot simply rely on next element visibility for poll and must test producer index when next element is not visible.
- Returns:
- a message from the queue if one is available,
null
iff empty
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peek
Description copied from interface:MessagePassingQueue
Called from the consumer thread subject to the restrictions appropriate to the implementation and according to theQueue.peek()
interface.- Returns:
- a message from the queue if one is available,
null
iff empty
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relaxedOffer
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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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
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
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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drainOneByOne
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fill
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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notAvailable
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fillOneByOne
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drain
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
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 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. -
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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