akka.dispatch

Class AbstractNodeQueue<T>

java.lang.Object

java.util.concurrent.atomic.AtomicReference<AbstractNodeQueue.Node<T>>

akka.dispatch.AbstractNodeQueue<T>

All Implemented Interfaces:

java.io.Serializable

Direct Known Subclasses:

NodeMessageQueue, SerializedSuspendableExecutionContext, TaskRunner.CommandQueue

public abstract class AbstractNodeQueue<T>
extends java.util.concurrent.atomic.AtomicReference<AbstractNodeQueue.Node<T>>

Lock-free MPSC linked queue implementation based on Dmitriy Vyukov's non-intrusive MPSC queue: http://www.1024cores.net/home/lock-free-algorithms/queues/non-intrusive-mpsc-node-based-queue This queue could be wait-free (i.e. without the spinning loops in peekNode and pollNode) if it were permitted to return null while the queue is not quite empty anymore but the enqueued element is not yet visible. This would break actor scheduling, though.

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	AbstractNodeQueue.Node<T>

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	AbstractNodeQueue()

Method Summary

Modifier and Type	Method and Description
void	add(T value) Add an element to the head of the queue.
void	addNode(AbstractNodeQueue.Node<T> n) Add an element to the head of the queue, providing the queue node to be used.
int	count() This method returns an upper bound on the queue size at the time it starts executing.
boolean	isEmpty() Query the queue whether it is empty right now.
T	peek() Query the queue tail for the next element without dequeuing it.
protected AbstractNodeQueue.Node<T>	peekNode() Query the queue tail for the next element without dequeuing it.
T	poll() Pull one item from the queue’s tail if there is one.
AbstractNodeQueue.Node<T>	pollNode() Pull one item from the queue, returning it within a queue node.

Methods inherited from class java.util.concurrent.atomic.AtomicReference

accumulateAndGet, compareAndSet, get, getAndAccumulate, getAndSet, getAndUpdate, lazySet, set, toString, updateAndGet, weakCompareAndSet

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

AbstractNodeQueue

protected AbstractNodeQueue()

Method Detail

peekNode

protected final AbstractNodeQueue.Node<T> peekNode()

Query the queue tail for the next element without dequeuing it. Use this method only from the consumer thread! !!! There is a copy of this code in pollNode() !!!

Returns:

queue node with element inside if there was one, or null if there was none

peek

public final T peek()

Query the queue tail for the next element without dequeuing it. Use this method only from the consumer thread!

Returns:

element if there was one, or null if there was none

add

public final void add(T value)

Add an element to the head of the queue. This method can be used from any thread.

Parameters:

value - the element to be added; must not be null

addNode

public final void addNode(AbstractNodeQueue.Node<T> n)

Add an element to the head of the queue, providing the queue node to be used. This method can be used from any thread.

Parameters:

n - the node containing the element to be added; both must not be null

isEmpty

public final boolean isEmpty()

Query the queue whether it is empty right now. This method can be used from any thread.

Returns:

true if queue was empty at some point in the past

count

public final int count()

This method returns an upper bound on the queue size at the time it starts executing. It may spuriously return smaller values (including zero) if the consumer pulls items out concurrently. This method can be used from any thread.

Returns:

an upper bound on queue length at some time in the past

poll

public final T poll()

Pull one item from the queue’s tail if there is one. Use this method only from the consumer thread!

Returns:

element if there was one, or null if there was none

pollNode

public final AbstractNodeQueue.Node<T> pollNode()

Pull one item from the queue, returning it within a queue node. Use this method only from the consumer thread!

Returns:

queue node with element inside if there was one, or null if there was none