Class MpscLinkedQueue<E>

Type Parameters:
E -
All Implemented Interfaces:
Iterable<E>, Collection<E>, Queue<E>

@SuppressAnimalSniffer public final class MpscLinkedQueue<E> extends BaseLinkedQueue<E>
This is a direct 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:
  1. Use inheritance to ensure no false sharing occurs between producer/consumer node reference fields.
  2. Use XCHG functionality to the best of the JDK ability (see differences in JDK7/8 impls).
The queue is initialized with a stub node which is set to both the producer and consumer node references. From this point follow the notes on offer/poll.
  • Constructor Details

    • MpscLinkedQueue

      public MpscLinkedQueue()
  • Method Details

    • xchgProducerNode

      protected LinkedQueueNode<E> xchgProducerNode(LinkedQueueNode<E> newVal)
    • offer

      public boolean offer(E nextValue)

      IMPLEMENTATION NOTES:
      Offer is allowed from multiple threads.
      Offer allocates a new node and:

      1. Swaps it atomically with current producer node (only one producer 'wins')
      2. Sets the new node as the node following from the swapped producer node
      This works because each producer is guaranteed to 'plant' a new node and link the old node. No 2 producers can get the same producer node as part of XCHG guarantee.
      See Also:
    • poll

      public E poll()

      IMPLEMENTATION NOTES:
      Poll is allowed from a SINGLE thread.
      Poll reads the next node from the consumerNode and:

      1. If it is null, the queue is assumed empty (though it might not be).
      2. If it is not null set it as the consumer node and return it's now evacuated value.
      This means the consumerNode.value is always null, which is also the starting point for the queue. Because null values are not allowed to be offered this is the only node with it's value set to null at any one time.
      See Also:
    • peek

      public E peek()