rx.internal.util.unsafe

Class ConcurrentCircularArrayQueue<E>

java.lang.Object

java.util.AbstractCollection<E>

java.util.AbstractQueue<E>

rx.internal.util.unsafe.ConcurrentCircularArrayQueue<E>

Type Parameters:

E -

All Implemented Interfaces:

java.lang.Iterable<E>, java.util.Collection<E>, java.util.Queue<E>

Direct Known Subclasses:

ConcurrentSequencedCircularArrayQueue, SpmcArrayQueue, SpscArrayQueue

public abstract class ConcurrentCircularArrayQueue<E>
extends java.util.AbstractQueue<E>

A concurrent access enabling class used by circular array based queues this class exposes an offset computation method along with differently memory fenced load/store methods into the underlying array. The class is pre-padded and the array is padded on either side to help with False sharing prvention. It is expected theat subclasses handle post padding.

Offset calculation is separate from access to enable the reuse of a give compute offset.

Load/Store methods using a buffer parameter are provided to allow the prevention of final field reload after a LoadLoad barrier.

Field Summary

Fields

Modifier and Type	Field and Description
protected E[]	buffer
protected static int	BUFFER_PAD
protected int	capacity
protected long	mask
protected static int	SPARSE_SHIFT

Constructor Summary

Constructors

Constructor and Description
ConcurrentCircularArrayQueue(int capacity)

Method Summary

Methods

Modifier and Type	Method and Description
protected long	calcElementOffset(long index)
boolean	isEmpty() This method's accuracy is subject to concurrent modifications happening as the observation is carried out.
java.util.Iterator<E>	iterator()
protected E	lpElement(E[] buffer, long offset) A plain load (no ordering/fences) of an element from a given offset.
protected E	lpElement(long offset) A plain load (no ordering/fences) of an element from a given offset.
protected E	lvElement(E[] buffer, long offset) A volatile load (load + LoadLoad barrier) of an element from a given offset.
protected E	lvElement(long offset) A volatile load (load + LoadLoad barrier) of an element from a given offset.
boolean	offer(M message) Called from a producer thread subject to the restrictions appropriate to the implementation and according to the Queue.offer(Object) interface (but failure to offer doesn't necessitate queue is full).
M	peek() Called from the consumer thread subject to the restrictions appropriate to the implementation and according to the Queue.peek() interface (barring the hard requirement on null returns).
M	poll() Called from the consumer thread subject to the restrictions appropriate to the implementation and according to the Queue.poll() interface (barring the hard requirement on null returns).
int	size() This method's accuracy is subject to concurrent modifications happening as the size is estimated and as such is a best effort rather than absolute value.
protected void	soElement(E[] buffer, long offset, E e) An ordered store(store + StoreStore barrier) of an element to a given offset
protected void	soElement(long offset, E e) An ordered store(store + StoreStore barrier) of an element to a given offset
protected void	spElement(E[] buffer, long offset, E e) A plain store (no ordering/fences) of an element to a given offset
protected void	spElement(long offset, E e) A plain store (no ordering/fences) of an element to a given offset

Methods inherited from class java.util.AbstractQueue

add, addAll, clear, element, remove

Methods inherited from class java.util.AbstractCollection

contains, containsAll, isEmpty, remove, removeAll, retainAll, size, toArray, toArray, toString

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.Queue

offer, peek, poll

Methods inherited from interface java.util.Collection

contains, containsAll, equals, hashCode, isEmpty, remove, removeAll, retainAll, size, toArray, toArray

Field Detail

SPARSE_SHIFT

protected static final int SPARSE_SHIFT

BUFFER_PAD

protected static final int BUFFER_PAD

See Also:

Constant Field Values

capacity

protected final int capacity

mask

protected final long mask

buffer

protected final E[] buffer

Constructor Detail

ConcurrentCircularArrayQueue

public ConcurrentCircularArrayQueue(int capacity)

Method Detail

calcElementOffset

protected final long calcElementOffset(long index)

Parameters:

index - desirable element index

Returns:

the offset in bytes within the array for a given index.

spElement

protected final void spElement(long offset,
             E e)

A plain store (no ordering/fences) of an element to a given offset

Parameters:

offset - computed via calcElementOffset(long)

e - a kitty

spElement

protected final void spElement(E[] buffer,
             long offset,
             E e)

A plain store (no ordering/fences) of an element to a given offset

Parameters:

buffer - this.buffer

offset - computed via calcElementOffset(long)

e - an orderly kitty

soElement

protected final void soElement(long offset,
             E e)

An ordered store(store + StoreStore barrier) of an element to a given offset

Parameters:

offset - computed via calcElementOffset(long)

e - an orderly kitty

soElement

protected final void soElement(E[] buffer,
             long offset,
             E e)

An ordered store(store + StoreStore barrier) of an element to a given offset

Parameters:

buffer - this.buffer

offset - computed via calcElementOffset(long)

e - an orderly kitty

lpElement

protected final E lpElement(long offset)

A plain load (no ordering/fences) of an element from a given offset.

Parameters:

offset - computed via calcElementOffset(long)

Returns:

the element at the offset

lpElement

protected final E lpElement(E[] buffer,
          long offset)

A plain load (no ordering/fences) of an element from a given offset.

Parameters:

buffer - this.buffer

offset - computed via calcElementOffset(long)

Returns:

the element at the offset

lvElement

protected final E lvElement(long offset)

A volatile load (load + LoadLoad barrier) of an element from a given offset.

Parameters:

offset - computed via calcElementOffset(long)

Returns:

the element at the offset

lvElement

protected final E lvElement(E[] buffer,
          long offset)

A volatile load (load + LoadLoad barrier) of an element from a given offset.

Parameters:

buffer - this.buffer

offset - computed via calcElementOffset(long)

Returns:

the element at the offset

iterator

public java.util.Iterator<E> iterator()

Specified by:

iterator in interface java.lang.Iterable<E>

Specified by:

iterator in interface java.util.Collection<E>

Specified by:

iterator in class java.util.AbstractCollection<E>

offer

public boolean offer(M message)

Called from a producer thread subject to the restrictions appropriate to the implementation and according to the Queue.offer(Object) interface (but failure to offer doesn't necessitate queue is full).

Parameters:

message -

Returns:

true if element was inserted into the queue, false if cannot enqueue

poll

public M poll()

Called from the consumer thread subject to the restrictions appropriate to the implementation and according to the Queue.poll() interface (barring the hard requirement on null returns).

Returns:

a message from the queue if one is available, null otherwise(not necessarily empty)

peek

public M peek()

Called from the consumer thread subject to the restrictions appropriate to the implementation and according to the Queue.peek() interface (barring the hard requirement on null returns).

Returns:

a message from the queue if one is available, null otherwise(not necessarily empty)

size

public int size()

This method's accuracy is subject to concurrent modifications happening as the size is estimated and as such is a best effort rather than absolute value. For some implementations this method may be O(n) rather than O(1).

Returns:

number of messages in the queue, between 0 and queue capacity or Integer.MAX_VALUE if not bounded

isEmpty

public boolean isEmpty()

This method's accuracy is subject to concurrent modifications happening as the observation is carried out.

Returns:

true if empty, false otherwise