org.jctools.queues.atomic.unpadded

Class MpmcAtomicUnpaddedArrayQueue<E>

java.lang.Object

java.util.AbstractCollection<E>

java.util.AbstractQueue<E>

org.jctools.queues.atomic.AtomicReferenceArrayQueue<E>

org.jctools.queues.atomic.SequencedAtomicReferenceArrayQueue<E>

org.jctools.queues.atomic.unpadded.MpmcAtomicUnpaddedArrayQueue<E>

All Implemented Interfaces:

Iterable<E>, Collection<E>, Queue<E>, IndexedQueueSizeUtil.IndexedQueue, MessagePassingQueue<E>, QueueProgressIndicators, SupportsIterator

public class MpmcAtomicUnpaddedArrayQueue<E>
extends SequencedAtomicReferenceArrayQueue<E>

NOTE: This class was automatically generated by org.jctools.queues.atomic.unpadded.JavaParsingAtomicUnpaddedArrayQueueGenerator which can found in the jctools-build module. The original source file is MpmcArrayQueue.java. A Multi-Producer-Multi-Consumer queue based on a ConcurrentCircularArrayQueue. 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:

1. 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. 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.
3. Power of 2 capacity: Actual elements buffer (and sequence buffer) is the closest power of 2 larger or equal to the requested capacity.

Nested Class Summary

Nested classes/interfaces inherited from interface org.jctools.queues.MessagePassingQueue

MessagePassingQueue.Consumer<T>, MessagePassingQueue.ExitCondition, MessagePassingQueue.Supplier<T>, MessagePassingQueue.WaitStrategy

Field Summary

Fields

Modifier and Type	Field and Description
static int	MAX_LOOK_AHEAD_STEP

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

Constructor Summary

Constructors

Constructor and Description
MpmcAtomicUnpaddedArrayQueue(int capacity)

Method Summary

Modifier and Type	Method and Description
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 w, 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.
long	lvConsumerIndex()
long	lvProducerIndex()
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.
E	peek() Called from the consumer thread subject to the restrictions appropriate to the implementation and according to the Queue.peek() interface.
E	poll() Called from the consumer thread subject to the restrictions appropriate to the implementation and according to the Queue.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.

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

Methods inherited from interface java.lang.Iterable

forEach

Field Detail

MAX_LOOK_AHEAD_STEP

public static final int MAX_LOOK_AHEAD_STEP

Constructor Detail

MpmcAtomicUnpaddedArrayQueue

public MpmcAtomicUnpaddedArrayQueue(int capacity)

Method Detail

offer

public boolean offer(E e)

Description copied from interface: MessagePassingQueue

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

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.

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

peek

public E peek()

Description copied from interface: MessagePassingQueue

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

Returns:

a message from the queue if one is available, null iff empty

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 to Queue.offer(Object) this method may return false without the queue being full.

Parameters:

e - 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,
                 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

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

lvConsumerIndex

public final long lvConsumerIndex()

lvProducerIndex

public final long lvProducerIndex()