org.compass.core.util.backport.java.util.concurrent
Class ConcurrentSkipListMap.Node

java.lang.Object
  org.compass.core.util.backport.java.util.concurrent.ConcurrentSkipListMap.Node

Enclosing class:

ConcurrentSkipListMap

static final class ConcurrentSkipListMap.Node
extends Object

Nodes hold keys and values, and are singly linked in sorted order, possibly with some intervening marker nodes. The list is headed by a dummy node accessible as head.node. The value field is declared only as Object because it takes special non-V values for marker and header nodes.

Field Summary

(package private) Object	key
(package private) ConcurrentSkipListMap.Node	next
(package private) Object	value

Constructor Summary

ConcurrentSkipListMap.Node(ConcurrentSkipListMap.Node next)
Creates a new marker node.

ConcurrentSkipListMap.Node(Object key, Object value, ConcurrentSkipListMap.Node next)
Creates a new regular node.

Method Summary

(package private) boolean	appendMarker(ConcurrentSkipListMap.Node f) Tries to append a deletion marker to this node.
(package private) boolean	casNext(ConcurrentSkipListMap.Node cmp, ConcurrentSkipListMap.Node val) compareAndSet next field
(package private) boolean	casValue(Object cmp, Object val) compareAndSet value field
(package private) AbstractMap.SimpleImmutableEntry	createSnapshot() Creates and returns a new SimpleImmutableEntry holding current mapping if this node holds a valid value, else null.
(package private) Object	getValidValue() Returns value if this node contains a valid key-value pair, else null.
(package private) void	helpDelete(ConcurrentSkipListMap.Node b, ConcurrentSkipListMap.Node f) Helps out a deletion by appending marker or unlinking from predecessor.
(package private) boolean	isBaseHeader() Returns true if this node is the header of base-level list.
(package private) boolean	isMarker() Returns true if this node is a marker.

Methods inherited from class java.lang.Object

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

Field Detail

key

final Object key

value

volatile Object value

next

volatile ConcurrentSkipListMap.Node next

Constructor Detail

ConcurrentSkipListMap.Node

ConcurrentSkipListMap.Node(Object key,
                           Object value,
                           ConcurrentSkipListMap.Node next)

Creates a new regular node.

ConcurrentSkipListMap.Node

ConcurrentSkipListMap.Node(ConcurrentSkipListMap.Node next)

Creates a new marker node. A marker is distinguished by having its value field point to itself. Marker nodes also have null keys, a fact that is exploited in a few places, but this doesn't distinguish markers from the base-level header node (head.node), which also has a null key.

Method Detail

casValue

boolean casValue(Object cmp,
                 Object val)

compareAndSet value field

casNext

boolean casNext(ConcurrentSkipListMap.Node cmp,
                ConcurrentSkipListMap.Node val)

compareAndSet next field

isMarker

boolean isMarker()

Returns true if this node is a marker. This method isn't actually called in any current code checking for markers because callers will have already read value field and need to use that read (not another done here) and so directly test if value points to node.

Parameters:

n - a possibly null reference to a node

Returns:

true if this node is a marker node

isBaseHeader

boolean isBaseHeader()

Returns true if this node is the header of base-level list.

Returns:

true if this node is header node

appendMarker

boolean appendMarker(ConcurrentSkipListMap.Node f)

Tries to append a deletion marker to this node.

Parameters:

f - the assumed current successor of this node

Returns:

true if successful

helpDelete

void helpDelete(ConcurrentSkipListMap.Node b,
                ConcurrentSkipListMap.Node f)

Helps out a deletion by appending marker or unlinking from predecessor. This is called during traversals when value field seen to be null.

Parameters:

b - predecessor

f - successor

getValidValue

Object getValidValue()

Returns value if this node contains a valid key-value pair, else null.

Returns:

this node's value if it isn't a marker or header or is deleted, else null.

createSnapshot

AbstractMap.SimpleImmutableEntry createSnapshot()

Creates and returns a new SimpleImmutableEntry holding current mapping if this node holds a valid value, else null.

Returns:

new entry or null