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Oracle® Fusion Middleware Java API Reference for Oracle Coherence 12c (12.1.3.0.0) E47890-01 |
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java.lang.Object
java.util.AbstractMap
com.tangosol.util.SafeSortedMap
public class SafeSortedMap
SafeSortedMap is an implementation of SortedMap
based on a skip-list that is structurally thread-safe. SafeSortedMap uses lockless (CAS-based) algorithms so all operations are performed without synchronization. In the presence of concurrent updates, SafeSortedMap iterators will reflect some state of the map, but will not throw ConcurrentModificationException or other unexpected exceptions.
Note that the ordering maintained by a sorted map (whether or not an explicit comparator is provided) must be consistent with equals if this sorted map is to correctly implement the Map interface. (See Comparable or Comparator for a precise definition of consistent with equals.) This is so because the Map interface is defined in terms of the equals operation, but a map performs all key comparisons using its compareTo (or compare) method, so two keys that are deemed equal by this method are, from the standpoint of the sorted map, equal. The behavior of a sorted map is well-defined even if its ordering is inconsistent with equals; it just fails to obey the general contract of the Map interface.
The structure of the SafeSortedMap is maintained in a 2-dimensional lattice:
Top | I3 -------------------------------> S5 -------------> | | I2 -------------> S2 -------------> S5 -------------> | | | I1 -------> S1 -> S2 -------> S4 -> S5 -------> S7 -> | | | | | | E -> E0 -> E1 -> E2 -> E3 -> E4 -> E5 -> E6 -> E7 ->
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:
The search path for the element E7 in the above example would be:
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.
In the above example, the steps to remove entry E3 would be:
The steps to remove E4 (indexed to level 1) would be:
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:
Nested Class Summary | |
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protected static class |
SafeSortedMap.BaseEntryNode BaseEntryNode is a synthetic EntryNode that serves as the "head" of the base entry list. |
protected static 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 static 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 class java.util.AbstractMap |
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java.util.AbstractMap.SimpleEntry, java.util.AbstractMap.SimpleImmutableEntry |
Nested classes/interfaces inherited from interface java.util.Map |
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java.util.Map.Entry |
Field Summary | |
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protected static java.lang.Object |
BASE_VALUE Placeholder for a non-existent (deleted) value. |
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_aflProbabilityThresholds The array of pre-computed probability thresholds for each level. |
protected static java.util.concurrent.atomic.AtomicReferenceFieldUpdater |
m_atomicUpdaterTopNode AtomicUpdater for the casTopNode operation. |
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_nSpan The span of the map. |
protected java.util.Random |
m_random The random-number generator for the map. |
protected static java.lang.Object |
NO_VALUE Placeholder for a non-existent (deleted) value. |
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 | |
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SafeSortedMap() Construct a new SafeSortedMap using the natural ordering of the Comparable keys in this map. |
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SafeSortedMap(java.util.Comparator comparator) Construct a new SafeSortedMap with the specified Comparator. |
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SafeSortedMap(java.util.Comparator comparator, int nSpan, int nLevelMax) Construct a new SafeSortedMap with the specified parameters. |
Method Summary | |
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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)^(l+1) and p(0)=1-(sum of p(l) over l=1..MAX_LEVEL). |
protected boolean |
casTopNode(SafeSortedMap.IndexNode nodeTopAssume, SafeSortedMap.IndexNode nodeTopNew) Atomically set specified IndexNode to the top node iff the current top node is the expected top node. |
void |
clear() |
java.util.Comparator |
comparator() |
protected static float[] |
computeProbabilityThresholds(int nLevelMax, int nSpan) Compute and return an array, indexed by level, of the probability thresholds used to determine what level an entry should be indexed to. |
boolean |
containsKey(java.lang.Object oKey) |
java.lang.String |
dump() Return a human-readable description of this map's internal state. |
java.util.Set |
entrySet() |
protected SafeSortedMap.EntryNode |
findNearest(SafeSortedMap.IndexNode nodeTop, java.lang.Object oKey, int nMode, boolean fFixLinks) Return the SkipNode closest to the specified key, or null. |
protected SafeSortedMap.EntryNode |
findNearestIndexedEntry(SafeSortedMap.IndexNode nodeTop, java.lang.Object oKey, int nMode) Return the EntryNode nearest to the specified key according to the specified search mode, or the synthetic base node if there is none. |
protected SafeSortedMap.EntryNode |
findPredecessor(SafeSortedMap.IndexNode nodeTop, java.lang.Object oKey) Return an EntryNode that compares strictly less than the specified key, or the synthetic base node if there is none. |
java.lang.Object |
firstKey() |
protected SafeSortedMap.EntryNode |
firstNode() Return the first valid EntryNode, or null if there are none. |
java.lang.Object |
get(java.lang.Object oKey) |
protected SafeSortedMap.BaseEntryNode |
getBaseNode() Return the base entry node. |
java.util.Map.Entry |
getEntry(java.lang.Object oKey) Locate a Map.Entry in this map based on its key. |
protected int |
getMaxLevel() Return the maximum index-level that this map is allowed to reach. |
protected float[] |
getProbabilityThresholds() Return the precomputed array of probability thresholds 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 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 void |
initialize() Initialize the index nodes. |
protected void |
insertIndex(SafeSortedMap.IndexNode nodeTop, SafeSortedMap.EntryNode nodeNew, int nLevelThis) Insert a index nodes for the specified newly inserted EntryNode, up to a random index-level. |
java.lang.Object |
lastKey() |
protected SafeSortedMap.EntryNode |
lastNode() Return the last valid EntryNode, or null if there are none. |
java.lang.Object |
put(java.lang.Object oKey, java.lang.Object oValue) |
java.lang.Object |
remove(java.lang.Object oKey) |
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 |
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clone, containsValue, equals, hashCode, isEmpty, keySet, putAll, toString, values |
Methods inherited from interface java.util.SortedMap |
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keySet, values |
Methods inherited from interface java.util.Map |
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containsValue, equals, hashCode, isEmpty, putAll |
Field Detail |
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protected static final int DEFAULT_SPAN
protected static final int DEFAULT_MAX_LEVEL
protected static final int SEARCH_EQ
protected static final int SEARCH_LT
protected static final int SEARCH_GT
protected static final int SEARCH_LTEQ
protected static final int SEARCH_GTEQ
protected static final java.lang.Object NO_VALUE
protected static final java.lang.Object BASE_VALUE
protected static final java.util.concurrent.atomic.AtomicReferenceFieldUpdater m_atomicUpdaterTopNode
protected final java.util.Comparator m_comparator
protected final int m_nLevelMax
protected final float[] m_aflProbabilityThresholds
protected int m_nSpan
protected final SafeSortedMap.ViewMap m_mapView
protected volatile SafeSortedMap.IndexNode m_nodeTop
protected java.util.Random m_random
Constructor Detail |
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public SafeSortedMap()
public SafeSortedMap(java.util.Comparator comparator)
comparator
- the comparator used to sort this mappublic SafeSortedMap(java.util.Comparator comparator, int nSpan, int nLevelMax)
comparator
- the comparator used to sort this map, or null for the entries' natural orderingnSpan
- the average span to use for each index-levelnLevelMax
- the maximum index-level to use for this mapMethod Detail |
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public int size()
size
in interface java.util.Map
size
in class java.util.AbstractMap
public boolean containsKey(java.lang.Object oKey)
containsKey
in interface java.util.Map
containsKey
in class java.util.AbstractMap
public java.util.Set entrySet()
entrySet
in interface java.util.Map
entrySet
in interface java.util.SortedMap
entrySet
in class java.util.AbstractMap
public java.lang.Object put(java.lang.Object oKey, java.lang.Object oValue)
put
in interface java.util.Map
put
in class java.util.AbstractMap
public java.lang.Object get(java.lang.Object oKey)
get
in interface java.util.Map
get
in class java.util.AbstractMap
public java.util.Map.Entry getEntry(java.lang.Object oKey)
Note: the behaviour of {#setValue} on the returned Entry is undefined in the presence of concurrent modifications
oKey
- the key to return an Entry forpublic java.lang.Object remove(java.lang.Object oKey)
remove
in interface java.util.Map
remove
in class java.util.AbstractMap
public void clear()
clear
in interface java.util.Map
clear
in class java.util.AbstractMap
public java.util.Comparator comparator()
comparator
in interface java.util.SortedMap
public java.util.SortedMap subMap(java.lang.Object fromKey, java.lang.Object toKey)
subMap
in interface java.util.SortedMap
public java.util.SortedMap headMap(java.lang.Object toKey)
headMap
in interface java.util.SortedMap
public java.util.SortedMap tailMap(java.lang.Object fromKey)
tailMap
in interface java.util.SortedMap
public java.lang.Object firstKey()
firstKey
in interface java.util.SortedMap
public java.lang.Object lastKey()
lastKey
in interface java.util.SortedMap
protected SafeSortedMap.ViewMap getViewMap()
protected float[] getProbabilityThresholds()
calculateRandomLevel()
protected java.util.Random getRandom()
protected int getMaxLevel()
protected int getSpan()
protected void initialize()
protected SafeSortedMap.IndexNode getTopNode()
protected void setTopNode(SafeSortedMap.IndexNode nodeTop)
nodeTop
- the new top index nodeprotected boolean casTopNode(SafeSortedMap.IndexNode nodeTopAssume, SafeSortedMap.IndexNode nodeTopNew)
nodeTopAssume
- the IndexNode assumed to be the current top nodenodeTopNew
- the new top nodeprotected SafeSortedMap.BaseEntryNode getBaseNode()
protected SafeSortedMap.EntryNode firstNode()
protected SafeSortedMap.EntryNode lastNode()
protected void insertIndex(SafeSortedMap.IndexNode nodeTop, SafeSortedMap.EntryNode nodeNew, int nLevelThis)
nodeTop
- the top index nodenodeNew
- the newly inserted EntryNodenLevelThis
- the level at which to index the specified EntryNodeprotected SafeSortedMap.EntryNode findNearest(SafeSortedMap.IndexNode nodeTop, java.lang.Object oKey, int nMode, boolean fFixLinks)
nodeTop
- the top index nodeoKey
- the key to search fornMode
- one of the SEARCH_* constantsfFixLinks
- true iff deletion links must be fixedprotected SafeSortedMap.EntryNode findPredecessor(SafeSortedMap.IndexNode nodeTop, java.lang.Object oKey)
Note: this method is merely guaranteed to return some EntryNode that is less than the specified node, not necessarily the node that is immediately less than the specified node
nodeTop
- the top index nodeoKey
- the key to find a predecessor forprotected SafeSortedMap.EntryNode findNearestIndexedEntry(SafeSortedMap.IndexNode nodeTop, java.lang.Object oKey, int nMode)
nodeTop
- the top index nodeoKey
- the key to find an indexed EntryNode fornMode
- SEARCH_LT or SEARCH_LTEQ)protected static float[] computeProbabilityThresholds(int nLevelMax, int nSpan)
Threshold values are in the range [0, 1). A randomly chosen value v in that range corresponds to a level l iff the following condition holds: threshold[l-1]<i/> <eq; v < threshold[l-1]<i/>
nLevelMax
- the maximum number of levels to compute thresholds fornSpan
- the span of this mapprotected int calculateRandomLevel()
For example, the probabilities (with span=2, and weight of 2) of returning the following levels are: 0 (no-index) - 3/4 1 - 1/8 2 - 1/16 3 - 1/32 ...
public java.lang.String dump()
public SafeSortedMap.Split split(java.lang.Object oKey)
SafeSortedMap.Split
of this map at the specified key.oKey
- the key at which to split the map
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Oracle® Fusion Middleware Java API Reference for Oracle Coherence 12c (12.1.3.0.0) E47890-01 |
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PREV CLASS NEXT CLASS | FRAMES NO FRAMES | |||||||
SUMMARY: NESTED | FIELD | CONSTR | METHOD | DETAIL: FIELD | CONSTR | METHOD |