Class SpscArrayQueue<E>

All Implemented Interfaces:
Iterable<E>, Collection<E>, Queue<E>, IndexedQueueSizeUtil.IndexedQueue, MessagePassingQueue<E>, QueueProgressIndicators, SupportsIterator

public class SpscArrayQueue<E> extends SpscArrayQueueL3Pad<E>
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.

  • Constructor Details

    • SpscArrayQueue

      public SpscArrayQueue(int capacity)
  • Method Details

    • 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
    • offerSlowPath

      private boolean offerSlowPath(E[] buffer, long mask, long producerIndex)
    • 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
    • drain

      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

      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 to MessagePassingQueue.Supplier.get() make sure you have read and understood these before using this method.