Package org.jctools.queues.atomic

Class SpscAtomicArrayQueue<E>

  • 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.

    • Field Detail

      • producerLimit

        protected long producerLimit

      • mask

        protected final int mask

    • Constructor Detail

      • SpscAtomicArrayQueue

        public SpscAtomicArrayQueue​(int capacity)

    • Method Detail

      • offer

        public boolean offer​(E e)
        Called from a producer thread subject to the restrictions appropriate to the implementation and according to the Queue.offer(Object) interface.

        This implementation is correct for single producer thread use only.

        Parameters:
        e - not null, will throw NPE if it is
        Returns:
        true if element was inserted into the queue, false iff full

      • poll

        public E poll()
        Called from the consumer thread subject to the restrictions appropriate to the implementation and according to the Queue.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

      • peek

        public E peek()
        Called from the consumer thread subject to the restrictions appropriate to the implementation and according to the Queue.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

      • 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 to Queue.offer(Object) this method may return false without the queue being full.
        Parameters:
        message - not null, will throw NPE if it is
        Returns:
        true if element was inserted into the queue, false if unable to offer

      • relaxedPoll

        public E relaxedPoll()
        Description copied from interface: MessagePassingQueue
        Called from the consumer thread subject to the restrictions appropriate to the implementation. As opposed to Queue.poll() this method may return null without the queue being empty.
        Returns:
        a message from the queue if one is available, null if unable to poll

      • relaxedPeek

        public E relaxedPeek()
        Description copied from interface: MessagePassingQueue
        Called from the consumer thread subject to the restrictions appropriate to the implementation. As opposed to Queue.peek() this method may return null without the queue being empty.
        Returns:
        a message from the queue if one is available, null if unable to peek

      • 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

      • 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

      • 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

      • 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

      • lvConsumerIndex

        public final long lvConsumerIndex()

      • lvProducerIndex

        public final long lvProducerIndex()

      • 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 interface Collection<E>
        Specified by:
        size in interface MessagePassingQueue<E>
        Specified by:
        size in class AbstractCollection<E>
        Returns:
        number of messages in the queue, between 0 and Integer.MAX_VALUE but less or equals to capacity (if bounded).

      • 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 interface QueueProgressIndicators
        Returns:
        the current value of the producer progress index

      • 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 interface QueueProgressIndicators
        Returns:
        the current value of the consumer progress index

      • 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 interface Collection<E>
        Specified by:
        iterator in interface Iterable<E>
        Specified by:
        iterator in class AbstractCollection<E>
        Returns:
        The iterator.