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com.tangosol.util
Class SafeSortedMap

java.lang.Object
java.util.AbstractMap
com.tangosol.util.SafeSortedMap

All Implemented Interfaces:

java.util.Map, java.util.SortedMap

public class SafeSortedMap

extends java.util.AbstractMap

implements java.util.SortedMap

SafeSortedMap is an implementation of SortedMap based on a skip-list that is structurally thread-safe. Read-only operations are performed without synchronization; mutations synchronize on the map. In the presence of concurrent updates, SafeSortedMap iterators will reflect some state of the map, but will not throw ConcurrentModificationException or other unexpected exceptions. <p/> The structure of the SafeSortedMap is maintained in a 2-dimensional lattice:

  Top
   |
  I3 -------------------------------> S5 ------------->
   |                                   |
  I2 -------------> S2 -------------> S5 ------------->
   |                 |                 |
  I1 -------> S1 -> S2 -------> S4 -> S5 -------> S7 ->
   |           |     |           |     |           |
  I0 -> E0 -> E1 -> E2 -> E3 -> E4 -> E5 -> E6 -> E7 ->
 

<p/> Searching for a key involves traversing, starting from the top index node, as far to the right at each index level, then down. For example, the search path for the element E4 in the above example would be:

1. compare E4 with S5 on index level 3; move down to level 2
2. compare E4 with S2 on index level 2; move right
3. compare E4 with S5 on index level 2; move down to level 1
4. compare E4 with S4 on index level 1; move right
5. move down

The search path for the element E7 in the above example would be:

1. compare E7 with S5 on index level 3; move right
2. move down to level 2
3. move down to level 1
4. compare E7 with S7 on index level 1; move right
5. move down

<p/> Removing a key involves inserting a temporary marker-entry while the entry pointers are fixed up. The marker node allows uncontended read threads to traverse the safely. Additionally, removing a key causes any index nodes for that key to be removed as well. Removals are synchronized on the map and proceed bottom up, removing the entry first followed by any index nodes in increasing index-level order. <p/> In the above example, the steps to remove entry E3 would be:

1. find LT search-path of Top->I3->S2->S2->E2
2. create new marker node D3
3. set D3 -> E4
4. set E3 -> D3
5. set E2 -> E3

The steps to remove E4 (indexed to level 1) would be:

1. find LT search-path of Top->I3->S2->S2->E3
2. create new marker node D4
3. set D4 -> E5
4. set E4 -> D4
5. set E3 -> E5
6. move up to level 1
7. set D4' -> S5
8. set S4 -> D4'
9. set S2 -> S5

Inserting a key happens in 'bottom-up' fashion, with the entry node being inserted first, (possibly) followed by index nodes of increasing level. Inserts are fully synchronized on the map. When inserting a new entry, an index level randomly computed such that, the probability that a given insertion will be indexed to level n is approximately given by: (1/k)ⁿ where k is the average span of each index level. In the above example, the steps to insert entry E3.5 at index-level 1 would be:

1. find LT search-path of Top->I3->S2->S2->E2
2. create new entry node E3.5
3. set E3.5 -> E4
4. set E2 -> E3.5
5. move up to level 1
6. create new entry node S3.5
7. set S3.5 -> S4
8. set S2 -> S3.5

<p/>

Since:

Coherence 3.5

Author:

rhl 2009.03.31

See Also:

Bill Pugh's original paper.

Nested Class Summary

protected class	SafeSortedMap.DeletedNode DeletedNode is a SkipNode that is used as a marker during deletion.
protected class	SafeSortedMap.EntryNode EntryNode represents a key-value mapping in this map.
protected class	SafeSortedMap.IndexNode IndexNode represents the start node in the map's lattice representation at a given index-level.
protected class	SafeSortedMap.SkipNode SkipNode is an entry or index node in the lattice for a SafeSortedMap's representation.
class	SafeSortedMap.Split Split encapsulates the headMap and tailMap of the SafeSortedMap at a given split-key and could be used as an optimization facility when both head and tail portions of the SortedMap are needed.
protected class	SafeSortedMap.ViewMap ViewMap provides a SortedMap view over a subset of the SafeSortedMap.

Nested classes/interfaces inherited from interface java.util.Map

java.util.Map.Entry

Field Summary

protected static int	DEFAULT_MAX_LEVEL The default limit on the index-level.
protected static int	DEFAULT_SPAN The default span value.
protected float[]	m_aflProbability The array of pre-computed probabilities for each level.
protected SafeSortedMap.SkipNode[]	m_aNodeBuffer The scratch buffer used by mutation operations to store the search path to the insertion/deletion site.
protected java.util.Comparator	m_comparator The comparator used to sort this map.
protected SafeSortedMap.ViewMap	m_mapView The default ViewMap (over the entire map's range).
protected int	m_nLevelMax The maximum number of index levels to use for this map.
protected SafeSortedMap.IndexNode	m_nodeTop The top index node.
protected int	m_nSize The memoized size of the map.
protected int	m_nSpan The span of the map.
protected java.util.Random	m_random The random-number generator for the map.
protected static int	SEARCH_EQ Search mode for equal-to.
protected static int	SEARCH_GT Search mode for strictly greater-than.
protected static int	SEARCH_GTEQ Search mode for greater-than or equal.
protected static int	SEARCH_LT Search mode for strictly less-than.
protected static int	SEARCH_LTEQ Search mode for less-than or equal.

Constructor Summary

SafeSortedMap()
Construct a new SafeSortedMap using the natural ordering of the Comparable keys in this map.

SafeSortedMap(java.util.Comparator comparator)
Construct a new SafeSortedMap with the specified Comparator.

SafeSortedMap(java.util.Comparator comparator, int nSpan, int nLevelMax)
Construct a new SafeSortedMap with the specified parameters.

Method Summary

protected int	calculateRandomLevel() Randomly generate a level value 0 <= L <= MAX_LEVEL, in such a way that the probability p(l) of generating level l is equal to p(l-1)/span and p(0)=1/span.
void	clear()
java.util.Comparator	comparator()
boolean	containsKey(java.lang.Object oKey)
protected java.lang.Object	deleteNode(SafeSortedMap.EntryNode node) Delete the specified node, as well any associated index nodes.
java.lang.String	dump() Return a human-readable description of this map's internal state.
java.util.Set	entrySet()
protected SafeSortedMap.EntryNode	findKey(java.lang.Object oKey) Return the EntryNode for the specified key if it is contained in this map, or null otherwise.
protected SafeSortedMap.SkipNode	findNearest(java.lang.Object oKey, int nMode) Return the SkipNode closest to the specified key, or null.
protected SafeSortedMap.SkipNode[]	findNearestPath(java.lang.Object oKey, int nMode) Return the search/index path to the node closest to the specified key.
protected SafeSortedMap.SkipNode[]	findNearestPath(java.lang.Object oKey, int nMode, SafeSortedMap.SkipNode[] aNodePath) Return the search/index path to the node closest to the specified key.
protected SafeSortedMap.SkipNode	findOnSameLevel(SafeSortedMap.SkipNode nodeStart, java.lang.Object oKey, int nMode) Find the closest SkipNode (according to the specified search mode) to the specified key, starting from the specified SkipNode.
java.lang.Object	firstKey()
java.lang.Object	get(java.lang.Object oKey)
java.util.Map.Entry	getEntry(java.lang.Object key) Locate an Entry in the this map based on its key.
protected int	getLevel() Return the current maximum level of this map's index (the highest level that any key has built an index node for).
protected int	getMaxLevel() Return the maximum index-level that this map is allowed to reach.
protected float[]	getProbabilities() Return the precomputed array of probability values used by this map to determine what index levels to build.
protected java.util.Random	getRandom() Return the random number generator for this map.
protected SafeSortedMap.SkipNode[]	getSearchBuffer() Return the buffer used to hold the search path for insertion/deletion operations.
protected int	getSpan() Return the span of this map.
protected SafeSortedMap.IndexNode	getTopNode() Return the top index node in the map.
protected SafeSortedMap.ViewMap	getViewMap() Return a view of the entire map.
java.util.SortedMap	headMap(java.lang.Object toKey)
protected boolean	insertNode(java.lang.Object oKey, java.lang.Object oValue) Insert a new EntryNode and (possibly) SkipNode(s) for the specified key and value in this skip-list, up to a random index-level.
java.lang.Object	lastKey()
java.lang.Object	put(java.lang.Object oKey, java.lang.Object oValue)
java.lang.Object	remove(java.lang.Object oKey)
protected SafeSortedMap.SkipNode	search(java.lang.Object oKey, int nMode, SafeSortedMap.IndexNode nodeTop, SafeSortedMap.SkipNode[] aNodePath) Return the search/index path to the node closest to the specified key.
protected void	setSearchBuffer(SafeSortedMap.SkipNode[] aNodeBuffer) Set the buffer used to hold the search path for insertion/deletion operations.
protected void	setSize(int nSize) Set the size of this map (cached to make the size() operation less expensive, since we already synchronize on all updates).
protected void	setTopNode(SafeSortedMap.IndexNode nodeTop) Set the top index node in the map.
int	size()
SafeSortedMap.Split	split(java.lang.Object oKey) Return a SafeSortedMap.Split of this map at the specified key.
java.util.SortedMap	subMap(java.lang.Object fromKey, java.lang.Object toKey)
java.util.SortedMap	tailMap(java.lang.Object fromKey)

Methods inherited from class java.util.AbstractMap

clone, containsValue, equals, hashCode, isEmpty, keySet, putAll, toString, values

Methods inherited from interface java.util.Map

containsValue, equals, hashCode, isEmpty, keySet, putAll, values

Field Detail

DEFAULT_SPAN

protected static final int DEFAULT_SPAN

The default span value.

See Also:

Constant Field Values

DEFAULT_MAX_LEVEL

protected static final int DEFAULT_MAX_LEVEL

The default limit on the index-level.

See Also:

Constant Field Values

SEARCH_EQ

protected static final int SEARCH_EQ

Search mode for equal-to.

See Also:

Constant Field Values

SEARCH_LT

protected static final int SEARCH_LT

Search mode for strictly less-than.

See Also:

Constant Field Values

SEARCH_GT

protected static final int SEARCH_GT

Search mode for strictly greater-than.

See Also:

Constant Field Values

SEARCH_LTEQ

protected static final int SEARCH_LTEQ

Search mode for less-than or equal.

See Also:

Constant Field Values

SEARCH_GTEQ

protected static final int SEARCH_GTEQ

Search mode for greater-than or equal.

See Also:

Constant Field Values

m_comparator

protected final java.util.Comparator m_comparator

The comparator used to sort this map.

m_nLevelMax

protected final int m_nLevelMax

The maximum number of index levels to use for this map.

m_aflProbability

protected final float[] m_aflProbability

The array of pre-computed probabilities for each level.

m_nSpan

protected int m_nSpan

The span of the map.

m_mapView

protected final SafeSortedMap.ViewMap m_mapView

The default ViewMap (over the entire map's range).

m_nodeTop

protected volatile SafeSortedMap.IndexNode m_nodeTop

The top index node. This is declared volatile so read operations can be unsynchronized.

m_aNodeBuffer

protected transient SafeSortedMap.SkipNode[] m_aNodeBuffer

The scratch buffer used by mutation operations to store the search path to the insertion/deletion site.

m_nSize

protected int m_nSize

The memoized size of the map. This is cached for efficiency.

m_random

protected java.util.Random m_random

The random-number generator for the map.

Constructor Detail

SafeSortedMap

public SafeSortedMap()

Construct a new SafeSortedMap using the natural ordering of the Comparable keys in this map.

SafeSortedMap

public SafeSortedMap(java.util.Comparator comparator)

Construct a new SafeSortedMap with the specified Comparator.

Parameters:

comparator - the comparator used to sort this map

SafeSortedMap

public SafeSortedMap(java.util.Comparator comparator,
                     int nSpan,
                     int nLevelMax)

Construct a new SafeSortedMap with the specified parameters.

Parameters:

comparator - the comparator used to sort this map

nSpan - the average span to use for each index-level

nLevelMax - the maximum index-level to use for this map

Method Detail

size

public int size()

Specified by:

size in interface java.util.Map

Overrides:

size in class java.util.AbstractMap

containsKey

public boolean containsKey(java.lang.Object oKey)

Specified by:

containsKey in interface java.util.Map

Overrides:

containsKey in class java.util.AbstractMap

entrySet

public java.util.Set entrySet()

Specified by:

entrySet in interface java.util.Map

Specified by:

entrySet in class java.util.AbstractMap

put

public java.lang.Object put(java.lang.Object oKey,
                            java.lang.Object oValue)

Specified by:

put in interface java.util.Map

Overrides:

put in class java.util.AbstractMap

get

public java.lang.Object get(java.lang.Object oKey)

Specified by:

get in interface java.util.Map

Overrides:

get in class java.util.AbstractMap

getEntry

public java.util.Map.Entry getEntry(java.lang.Object key)

Locate an Entry in the this map based on its key.

Parameters:

key - the key object to search for

Returns:

the Entry or null if the entry does not exist

remove

public java.lang.Object remove(java.lang.Object oKey)

Specified by:

remove in interface java.util.Map

Overrides:

remove in class java.util.AbstractMap

clear

public void clear()

Specified by:

clear in interface java.util.Map

Overrides:

clear in class java.util.AbstractMap

comparator

public java.util.Comparator comparator()

Specified by:

comparator in interface java.util.SortedMap

subMap

public java.util.SortedMap subMap(java.lang.Object fromKey,
                                  java.lang.Object toKey)

Specified by:

subMap in interface java.util.SortedMap

headMap

public java.util.SortedMap headMap(java.lang.Object toKey)

Specified by:

headMap in interface java.util.SortedMap

tailMap

public java.util.SortedMap tailMap(java.lang.Object fromKey)

Specified by:

tailMap in interface java.util.SortedMap

firstKey

public java.lang.Object firstKey()

Specified by:

firstKey in interface java.util.SortedMap

lastKey

public java.lang.Object lastKey()

Specified by:

lastKey in interface java.util.SortedMap

getViewMap

protected SafeSortedMap.ViewMap getViewMap()

Return a view of the entire map.

Returns:

a view of the entire map

setSize

protected void setSize(int nSize)

Set the size of this map (cached to make the size() operation less expensive, since we already synchronize on all updates). <p/> Note: caller must hold synchronization on the map

Parameters:

nSize - the new size of the map

getProbabilities

protected float[] getProbabilities()

Return the precomputed array of probability values used by this map to determine what index levels to build.

Returns:

the precomputed array of probability values

See Also:

calculateRandomLevel()

getRandom

protected java.util.Random getRandom()

Return the random number generator for this map.

Returns:

the random number generator for this map

getLevel

protected int getLevel()

Return the current maximum level of this map's index (the highest level that any key has built an index node for).

Returns:

the current maximum level this map's index

getMaxLevel

protected int getMaxLevel()

Return the maximum index-level that this map is allowed to reach.

Returns:

the maximum index-level that this map is allowed to reach

getSpan

protected int getSpan()

Return the span of this map.

Returns:

the span of this map

getTopNode

protected SafeSortedMap.IndexNode getTopNode()

Return the top index node in the map.

Returns:

the top index node in the map

setTopNode

protected void setTopNode(SafeSortedMap.IndexNode nodeTop)

Set the top index node in the map. <p/> Note: caller must hold synchronization on the map

Parameters:

nodeTop - the new top index node

getSearchBuffer

protected SafeSortedMap.SkipNode[] getSearchBuffer()

Return the buffer used to hold the search path for insertion/deletion operations.

Returns:

the search path buffer

setSearchBuffer

protected void setSearchBuffer(SafeSortedMap.SkipNode[] aNodeBuffer)

Set the buffer used to hold the search path for insertion/deletion operations. <p/> Note: caller must hold synchronization on the map

Parameters:

aNodeBuffer - the new search path buffer

insertNode

protected boolean insertNode(java.lang.Object oKey,
                             java.lang.Object oValue)

Insert a new EntryNode and (possibly) SkipNode(s) for the specified key and value in this skip-list, up to a random index-level. Return true if the key was inserted, or false otherwise (if an intervening insert was made for the same key).

Parameters:

oKey - the key to insert

oValue - the value to insert

Returns:

true if the key was successfully inserted, false otherwise

deleteNode

protected java.lang.Object deleteNode(SafeSortedMap.EntryNode node)

Delete the specified node, as well any associated index nodes. Return the previous value associated with the node, or null if the node was already removed by an intervening thread.

Returns:

the previous value associated with the node, or null

findOnSameLevel

protected SafeSortedMap.SkipNode findOnSameLevel(SafeSortedMap.SkipNode nodeStart,
                                                 java.lang.Object oKey,
                                                 int nMode)

Find the closest SkipNode (according to the specified search mode) to the specified key, starting from the specified SkipNode. <p/> Note: SEARCH_GT* modes that exhaust the level, return null while SEARCH_LT* modes may return the synthetic IndexNode. <p/> Note: this method does not synchronize internally, so it is possible that the returned node has been or will be deleted from the map.

Parameters:

nodeStart - the SkipNode to start searching from

oKey - the key to search for

nMode - one of the SEARCH_* constants

Returns:

the SkipNode that matches the key most closely, or null

findKey

protected SafeSortedMap.EntryNode findKey(java.lang.Object oKey)

Return the EntryNode for the specified key if it is contained in this map, or null otherwise.

Parameters:

oKey - the key to search for

Returns:

the EntryNode for the specified key, or null if the key is not found

findNearest

protected SafeSortedMap.SkipNode findNearest(java.lang.Object oKey,
                                             int nMode)

Return the SkipNode closest to the specified key, or null.

Parameters:

oKey - the key to search for

nMode - one of the SEARCH_* constants

Returns:

the SkipNode closest to the specified key, or null

findNearestPath

protected SafeSortedMap.SkipNode[] findNearestPath(java.lang.Object oKey,
                                                   int nMode)

Return the search/index path to the node closest to the specified key. <p/> Note: the caller must hold synchronization on the map.

Parameters:

oKey - the key to search for

nMode - one of the SEARCH_* constants

Returns:

the search/index path to the node closest to the specified key

findNearestPath

protected SafeSortedMap.SkipNode[] findNearestPath(java.lang.Object oKey,
                                                   int nMode,
                                                   SafeSortedMap.SkipNode[] aNodePath)

Return the search/index path to the node closest to the specified key.

Parameters:

oKey - the key to search for

nMode - one of the SEARCH_* constants

aNodePath - the array into which the search path will be stored if it is the correct size; otherwise a new array will be allocated

Returns:

the search/index path to the node closest to the specified key

search

protected SafeSortedMap.SkipNode search(java.lang.Object oKey,
                                        int nMode,
                                        SafeSortedMap.IndexNode nodeTop,
                                        SafeSortedMap.SkipNode[] aNodePath)

Return the search/index path to the node closest to the specified key.

Parameters:

oKey - the key to search for

nMode - one of the SEARCH_* constants

nodeTop - the top index node to start searching from

aNodePath - the search/index path recorded by the search to the node closest to the specified key, according to the specified search mode. May be null.

Returns:

the IndexNode or EntryNode at level 0, closest to the specified key, according to the specified search mode

calculateRandomLevel

protected int calculateRandomLevel()

Randomly generate a level value 0 <= L <= MAX_LEVEL, in such a way that the probability p(l) of generating level l is equal to p(l-1)/span and p(0)=1/span.

Returns:

a random level number between 0 and MAX_LEVEL

dump

public java.lang.String dump()

Return a human-readable description of this map's internal state.

Returns:

a human-readable description of this map's internal state

split

public SafeSortedMap.Split split(java.lang.Object oKey)

Return a SafeSortedMap.Split of this map at the specified key.

Parameters:

oKey - the key at which to split the map

Returns:

a Split of this map at the specified key

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