Top Description Fields Constructors Methods
io.netty.util.internal.shaded.org.jctools.queues

public Class MpmcArrayQueue<E>

Additional top-level classes in compilation unit: MpmcArrayQueueL1Pad, MpmcArrayQueueProducerIndexField, MpmcArrayQueueL2Pad, MpmcArrayQueueConsumerIndexField, MpmcArrayQueueL3Pad.

extends MpmcArrayQueueL3Pad<E>
Class Inheritance
Imports
io.netty.util.internal.shaded.org.jctools.util.RangeUtil
A Multi-Producer-Multi-Consumer queue based on a io.netty.util.internal.shaded.org.jctools.queues.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.

Field Summary

Modifier and TypeField and Description
private final int
lookAheadStep

public static final int
MAX_LOOK_AHEAD_STEP

Inherited from io.netty.util.internal.shaded.org.jctools.queues.MpmcArrayQueueL3Pad:
b000b001b002b003b004b005b006b007b010b011b012b013b014b015b016b017b020b021b022b023b024b025b026b027b030b031b032b033b034b035b036b037b040b041b042b043b044b045b046b047b050b051b052b053b054b055b056b057b060b061b062b063b064b065b066b067b070b071b072b073b074b075b076b077b100b101b102b103b104b105b106b107b110b111b112b113b114b115b116b117b120b121b122b123b124b125b126b127b130b131b132b133b134b135b136b137b140b141b142b143b144b145b146b147b150b151b152b153b154b155b156b157b160b161b162b163b164b165b166b167b170b171b172b173b174b175b176b177

Constructor Summary

AccessConstructor and Description
public
MpmcArrayQueue(final int capacity)

Method Summary

Modifier and TypeMethod and Description
public int
drain(MessagePassingQueue.Consumer<E> c, int limit)

Implements io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.drain.

Remove up to limit elements from the queue and hand to consume.
public int
drain(MessagePassingQueue.Consumer<E> c)

Implements io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.drain.

Remove all available item from the queue and hand to consume.
public void
drain(MessagePassingQueue.Consumer<E> c, MessagePassingQueue.WaitStrategy w, MessagePassingQueue.ExitCondition exit)

Implements io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.drain.

Remove elements from the queue and hand to consume forever.
private int
drainOneByOne(MessagePassingQueue.Consumer<E> c, int limit)

public int
fill(MessagePassingQueue.Supplier<E> s, int limit)

Implements io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.fill.

Stuff the queue with up to limit elements from the supplier.
public int
fill(MessagePassingQueue.Supplier<E> s)

Implements io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.fill.

Stuff the queue with elements from the supplier.
public void
fill(MessagePassingQueue.Supplier<E> s, MessagePassingQueue.WaitStrategy wait, MessagePassingQueue.ExitCondition exit)

Implements io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.fill.

Stuff the queue with elements from the supplier forever.
private int
fillOneByOne(MessagePassingQueue.Supplier<E> s, int limit)

private boolean
notAvailable(long index, long mask, long[] sBuffer, long expectedSeq)

public boolean
offer(final E
not null, will throw NPE if it is
e)

Implements io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.offer, java.util.Queue.offer.

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

Implements io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.peek, java.util.Queue.peek.

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

Implements io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.poll, java.util.Queue.poll.

Called from the consumer thread subject to the restrictions appropriate to the implementation and according to the Queue#poll() interface.
public boolean
relaxedOffer(E
not null, will throw NPE if it is
e)

Implements io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.relaxedOffer.

Called from a producer thread subject to the restrictions appropriate to the implementation.
public E
relaxedPeek()

Implements io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.relaxedPeek.

Called from the consumer thread subject to the restrictions appropriate to the implementation.
public E
relaxedPoll()

Implements io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.relaxedPoll.

Called from the consumer thread subject to the restrictions appropriate to the implementation.

Field Detail

lookAheadStepback to summary
private final int lookAheadStep
MAX_LOOK_AHEAD_STEPback to summary
public static final int MAX_LOOK_AHEAD_STEP

Constructor Detail

MpmcArrayQueueback to summary
public MpmcArrayQueue(final int capacity)

Method Detail

drainback to summary
public int drain(MessagePassingQueue.Consumer<E> c, int limit)

Implements io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.drain.

Doc from io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.drain.

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 Consumer#accept make sure you have read and understood these before using this method.

Returns:int

the number of polled elements

Annotations
@Override
drainback to summary
public int drain(MessagePassingQueue.Consumer<E> c)

Implements io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.drain.

Doc from io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.drain.

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 Consumer#accept make sure you have read and understood these before using this method.

Returns:int

the number of polled elements

Annotations
@Override
drainback to summary
public void drain(MessagePassingQueue.Consumer<E> c, MessagePassingQueue.WaitStrategy w, MessagePassingQueue.ExitCondition exit)

Implements io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.drain.

Doc from io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.drain.

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 Consumer#accept make sure you have read and understood these before using this method.

Annotations
@Override
drainOneByOneback to summary
private int drainOneByOne(MessagePassingQueue.Consumer<E> c, int limit)
fillback to summary
public int fill(MessagePassingQueue.Supplier<E> s, int limit)

Implements io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.fill.

Doc from io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.fill.

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 Supplier#get make sure you have read and understood these before using this method.

Returns:int

the number of offered elements

Annotations
@Override
fillback to summary
public int fill(MessagePassingQueue.Supplier<E> s)

Implements io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.fill.

Doc from io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.fill.

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 Supplier#get make sure you have read and understood these before using this method.

Returns:int

the number of offered elements

Annotations
@Override
fillback to summary
public void fill(MessagePassingQueue.Supplier<E> s, MessagePassingQueue.WaitStrategy wait, MessagePassingQueue.ExitCondition exit)

Implements io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.fill.

Doc from io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.fill.

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 Supplier#get

Warning

Explicit assumptions are made with regards to Supplier#get make sure you have read and understood these before using this method.

Annotations
@Override
fillOneByOneback to summary
private int fillOneByOne(MessagePassingQueue.Supplier<E> s, int limit)
notAvailableback to summary
private boolean notAvailable(long index, long mask, long[] sBuffer, long expectedSeq)
offerback to summary
public boolean offer(final E e)

Implements io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.offer, java.util.Queue.offer.

Doc from io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.offer.

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

Parameters
e:E

not null, will throw NPE if it is

Returns:boolean

true if element was inserted into the queue, false iff full

Annotations
@Override
peekback to summary
public E peek()

Implements io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.peek, java.util.Queue.peek.

Doc from io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.peek.

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

Returns:E

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

Annotations
@Override
pollback to summary
public E poll()

Implements io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.poll, java.util.Queue.poll.

Doc from io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.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:E

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

Annotations
@Override
relaxedOfferback to summary
public boolean relaxedOffer(E e)

Implements io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.relaxedOffer.

Doc from io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.relaxedOffer.

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:E

not null, will throw NPE if it is

Returns:boolean

true if element was inserted into the queue, false if unable to offer

Annotations
@Override
relaxedPeekback to summary
public E relaxedPeek()

Implements io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.relaxedPeek.

Doc from io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.relaxedPeek.

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:E

a message from the queue if one is available, null if unable to peek

Annotations
@Override
relaxedPollback to summary
public E relaxedPoll()

Implements io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.relaxedPoll.

Doc from io.netty.util.internal.shaded.org.jctools.queues.MessagePassingQueue.relaxedPoll.

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:E

a message from the queue if one is available, null if unable to poll

Annotations
@Override