edu.emory.mathcs.backport.java.util.concurrent

Class ConcurrentSkipListMap

Implemented Interfaces:
Cloneable, ConcurrentMap, ConcurrentNavigableMap, Map, NavigableMap, java.io.Serializable, SortedMap

public class ConcurrentSkipListMap
extends AbstractMap
implements ConcurrentNavigableMap, Cloneable, java.io.Serializable

A scalable concurrent ConcurrentNavigableMap implementation. The map is sorted according to the natural ordering of its keys, or by a Comparator provided at map creation time, depending on which constructor is used.

This class implements a concurrent variant of SkipLists providing expected average log(n) time cost for the containsKey, get, put and remove operations and their variants. Insertion, removal, update, and access operations safely execute concurrently by multiple threads. Iterators are weakly consistent, returning elements reflecting the state of the map at some point at or since the creation of the iterator. They do not throw java.util.ConcurrentModificationException, and may proceed concurrently with other operations. Ascending key ordered views and their iterators are faster than descending ones.

All Map.Entry pairs returned by methods in this class and its views represent snapshots of mappings at the time they were produced. They do not support the Entry.setValue method. (Note however that it is possible to change mappings in the associated map using put, putIfAbsent, or replace, depending on exactly which effect you need.)

Beware that, unlike in most collections, the size method is not a constant-time operation. Because of the asynchronous nature of these maps, determining the current number of elements requires a traversal of the elements. Additionally, the bulk operations putAll, equals, and clear are not guaranteed to be performed atomically. For example, an iterator operating concurrently with a putAll operation might view only some of the added elements.

This class and its views and iterators implement all of the optional methods of the Map and Iterator interfaces. Like most other concurrent collections, this class does not permit the use of null keys or values because some null return values cannot be reliably distinguished from the absence of elements.

This class is a member of the ../../../../../../../../technotes/guides/collections/index.html"> Java Collections Framework.

Author:
Doug Lea
Since:
1.6
See Also:
Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from class edu.emory.mathcs.backport.java.util.AbstractMap

AbstractMap.SimpleEntry, AbstractMap.SimpleImmutableEntry

Constructor Summary

ConcurrentSkipListMap()
Constructs a new, empty map, sorted according to the natural ordering of the keys.
ConcurrentSkipListMap(Comparator comparator)
Constructs a new, empty map, sorted according to the specified comparator.
ConcurrentSkipListMap(Map m)
Constructs a new map containing the same mappings as the given map, sorted according to the natural ordering of the keys.
ConcurrentSkipListMap(SortedMap m)
Constructs a new map containing the same mappings and using the same ordering as the specified sorted map.

Method Summary

Map.Entry
ceilingEntry(Object key)
Returns a key-value mapping associated with the least key greater than or equal to the given key, or null if there is no such entry.
Object
ceilingKey(Object key)
void
clear()
Removes all of the mappings from this map.
Object
clone()
Returns a shallow copy of this ConcurrentSkipListMap instance.
Comparator
comparator()
boolean
containsKey(Object key)
Returns true if this map contains a mapping for the specified key.
boolean
containsValue(Object value)
Returns true if this map maps one or more keys to the specified value.
NavigableSet
descendingKeySet()
NavigableMap
descendingMap()
Set
entrySet()
Returns a Set view of the mappings contained in this map.
boolean
equals(Object o)
Compares the specified object with this map for equality.
Map.Entry
firstEntry()
Returns a key-value mapping associated with the least key in this map, or null if the map is empty.
Object
firstKey()
Map.Entry
floorEntry(Object key)
Returns a key-value mapping associated with the greatest key less than or equal to the given key, or null if there is no such key.
Object
floorKey(Object key)
Object
get(Object key)
Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.
SortedMap
headMap(Object toKey)
NavigableMap
headMap(Object toKey, boolean inclusive)
Map.Entry
higherEntry(Object key)
Returns a key-value mapping associated with the least key strictly greater than the given key, or null if there is no such key.
Object
higherKey(Object key)
boolean
isEmpty()
Returns true if this map contains no key-value mappings.
Set
keySet()
Returns a NavigableSet view of the keys contained in this map.
Map.Entry
lastEntry()
Returns a key-value mapping associated with the greatest key in this map, or null if the map is empty.
Object
lastKey()
Map.Entry
lowerEntry(Object key)
Returns a key-value mapping associated with the greatest key strictly less than the given key, or null if there is no such key.
Object
lowerKey(Object key)
NavigableSet
navigableKeySet()
Map.Entry
pollFirstEntry()
Removes and returns a key-value mapping associated with the least key in this map, or null if the map is empty.
Map.Entry
pollLastEntry()
Removes and returns a key-value mapping associated with the greatest key in this map, or null if the map is empty.
Object
put(Object key, Object value)
Associates the specified value with the specified key in this map.
Object
putIfAbsent(Object key, Object value)
Object
remove(Object key)
Removes the mapping for the specified key from this map if present.
boolean
remove(Object key, Object value)
Object
replace(Object key, Object value)
boolean
replace(Object key, Object oldValue, Object newValue)
int
size()
Returns the number of key-value mappings in this map.
SortedMap
subMap(Object fromKey, Object toKey)
NavigableMap
subMap(Object fromKey, boolean fromInclusive, Object toKey, boolean toInclusive)
SortedMap
tailMap(Object fromKey)
NavigableMap
tailMap(Object fromKey, boolean inclusive)
Collection
values()
Returns a Collection view of the values contained in this map.

Methods inherited from class edu.emory.mathcs.backport.java.util.AbstractMap

keySet

Constructor Details

ConcurrentSkipListMap

public ConcurrentSkipListMap()
Constructs a new, empty map, sorted according to the natural ordering of the keys.

ConcurrentSkipListMap

public ConcurrentSkipListMap(Comparator comparator)
Constructs a new, empty map, sorted according to the specified comparator.
Parameters:
comparator - the comparator that will be used to order this map. If null, the natural ordering of the keys will be used.

ConcurrentSkipListMap

public ConcurrentSkipListMap(Map m)
Constructs a new map containing the same mappings as the given map, sorted according to the natural ordering of the keys.
Parameters:
m - the map whose mappings are to be placed in this map

ConcurrentSkipListMap

public ConcurrentSkipListMap(SortedMap m)
Constructs a new map containing the same mappings and using the same ordering as the specified sorted map.
Parameters:
m - the sorted map whose mappings are to be placed in this map, and whose comparator is to be used to sort this map

Method Details

ceilingEntry

public Map.Entry ceilingEntry(Object key)
Returns a key-value mapping associated with the least key greater than or equal to the given key, or null if there is no such entry. The returned entry does not support the Entry.setValue method.
Specified by:
ceilingEntry in interface NavigableMap

ceilingKey

public Object ceilingKey(Object key)
Specified by:
ceilingKey in interface NavigableMap

clear

public void clear()
Removes all of the mappings from this map.

clone

public Object clone()
Returns a shallow copy of this ConcurrentSkipListMap instance. (The keys and values themselves are not cloned.)
Returns:
a shallow copy of this map

comparator

public Comparator comparator()

containsKey

public boolean containsKey(Object key)
Returns true if this map contains a mapping for the specified key.
Parameters:
key - key whose presence in this map is to be tested
Returns:
true if this map contains a mapping for the specified key

containsValue

public boolean containsValue(Object value)
Returns true if this map maps one or more keys to the specified value. This operation requires time linear in the map size.
Parameters:
value - value whose presence in this map is to be tested
Returns:
true if a mapping to value exists; false otherwise

descendingKeySet

public NavigableSet descendingKeySet()
Specified by:
descendingKeySet in interface ConcurrentNavigableMap
descendingKeySet in interface NavigableMap

descendingMap

public NavigableMap descendingMap()
Specified by:
descendingMap in interface ConcurrentNavigableMap
descendingMap in interface NavigableMap

entrySet

public Set entrySet()
Returns a Set view of the mappings contained in this map. The set's iterator returns the entries in ascending key order. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.

The view's iterator is a "weakly consistent" iterator that will never throw java.util.ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.

The Map.Entry elements returned by iterator.next() do not support the setValue operation.

Returns:
a set view of the mappings contained in this map, sorted in ascending key order

equals

public boolean equals(Object o)
Compares the specified object with this map for equality. Returns true if the given object is also a map and the two maps represent the same mappings. More formally, two maps m1 and m2 represent the same mappings if m1.entrySet().equals(m2.entrySet()). This operation may return misleading results if either map is concurrently modified during execution of this method.
Parameters:
o - object to be compared for equality with this map
Returns:
true if the specified object is equal to this map

firstEntry

public Map.Entry firstEntry()
Returns a key-value mapping associated with the least key in this map, or null if the map is empty. The returned entry does not support the Entry.setValue method.
Specified by:
firstEntry in interface NavigableMap

firstKey

public Object firstKey()

floorEntry

public Map.Entry floorEntry(Object key)
Returns a key-value mapping associated with the greatest key less than or equal to the given key, or null if there is no such key. The returned entry does not support the Entry.setValue method.
Specified by:
floorEntry in interface NavigableMap
Parameters:
key - the key

floorKey

public Object floorKey(Object key)
Specified by:
floorKey in interface NavigableMap
Parameters:
key - the key

get

public Object get(Object key)
Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.

More formally, if this map contains a mapping from a key k to a value v such that key compares equal to k according to the map's ordering, then this method returns v; otherwise it returns null. (There can be at most one such mapping.)


headMap

public SortedMap headMap(Object toKey)
Specified by:
headMap in interface ConcurrentNavigableMap
headMap in interface NavigableMap

headMap

public NavigableMap headMap(Object toKey,
                            boolean inclusive)
Specified by:
headMap in interface ConcurrentNavigableMap
headMap in interface NavigableMap

higherEntry

public Map.Entry higherEntry(Object key)
Returns a key-value mapping associated with the least key strictly greater than the given key, or null if there is no such key. The returned entry does not support the Entry.setValue method.
Specified by:
higherEntry in interface NavigableMap
Parameters:
key - the key

higherKey

public Object higherKey(Object key)
Specified by:
higherKey in interface NavigableMap
Parameters:
key - the key

isEmpty

public boolean isEmpty()
Returns true if this map contains no key-value mappings.
Returns:
true if this map contains no key-value mappings

keySet

public Set keySet()
Returns a NavigableSet view of the keys contained in this map. The set's iterator returns the keys in ascending order. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll, retainAll, and clear operations. It does not support the add or addAll operations.

The view's iterator is a "weakly consistent" iterator that will never throw java.util.ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.

This method is equivalent to method navigableKeySet.

Specified by:
keySet in interface ConcurrentNavigableMap
Overrides:
keySet in interface AbstractMap
Returns:
a navigable set view of the keys in this map

lastEntry

public Map.Entry lastEntry()
Returns a key-value mapping associated with the greatest key in this map, or null if the map is empty. The returned entry does not support the Entry.setValue method.
Specified by:
lastEntry in interface NavigableMap

lastKey

public Object lastKey()

lowerEntry

public Map.Entry lowerEntry(Object key)
Returns a key-value mapping associated with the greatest key strictly less than the given key, or null if there is no such key. The returned entry does not support the Entry.setValue method.
Specified by:
lowerEntry in interface NavigableMap

lowerKey

public Object lowerKey(Object key)
Specified by:
lowerKey in interface NavigableMap

navigableKeySet

public NavigableSet navigableKeySet()
Specified by:
navigableKeySet in interface ConcurrentNavigableMap
navigableKeySet in interface NavigableMap

pollFirstEntry

public Map.Entry pollFirstEntry()
Removes and returns a key-value mapping associated with the least key in this map, or null if the map is empty. The returned entry does not support the Entry.setValue method.
Specified by:
pollFirstEntry in interface NavigableMap

pollLastEntry

public Map.Entry pollLastEntry()
Removes and returns a key-value mapping associated with the greatest key in this map, or null if the map is empty. The returned entry does not support the Entry.setValue method.
Specified by:
pollLastEntry in interface NavigableMap

put

public Object put(Object key,
                  Object value)
Associates the specified value with the specified key in this map. If the map previously contained a mapping for the key, the old value is replaced.
Parameters:
key - key with which the specified value is to be associated
value - value to be associated with the specified key
Returns:
the previous value associated with the specified key, or null if there was no mapping for the key

putIfAbsent

public Object putIfAbsent(Object key,
                          Object value)
Specified by:
putIfAbsent in interface ConcurrentMap
Returns:
the previous value associated with the specified key, or null if there was no mapping for the key

remove

public Object remove(Object key)
Removes the mapping for the specified key from this map if present.
Parameters:
key - key for which mapping should be removed
Returns:
the previous value associated with the specified key, or null if there was no mapping for the key

remove

public boolean remove(Object key,
                      Object value)
Specified by:
remove in interface ConcurrentMap

replace

public Object replace(Object key,
                      Object value)
Specified by:
replace in interface ConcurrentMap
Returns:
the previous value associated with the specified key, or null if there was no mapping for the key

replace

public boolean replace(Object key,
                       Object oldValue,
                       Object newValue)
Specified by:
replace in interface ConcurrentMap

size

public int size()
Returns the number of key-value mappings in this map. If this map contains more than Integer.MAX_VALUE elements, it returns Integer.MAX_VALUE.

Beware that, unlike in most collections, this method is NOT a constant-time operation. Because of the asynchronous nature of these maps, determining the current number of elements requires traversing them all to count them. Additionally, it is possible for the size to change during execution of this method, in which case the returned result will be inaccurate. Thus, this method is typically not very useful in concurrent applications.

Returns:
the number of elements in this map

subMap

public SortedMap subMap(Object fromKey,
                        Object toKey)
Specified by:
subMap in interface ConcurrentNavigableMap
subMap in interface NavigableMap

subMap

public NavigableMap subMap(Object fromKey,
                           boolean fromInclusive,
                           Object toKey,
                           boolean toInclusive)
Specified by:
subMap in interface ConcurrentNavigableMap
subMap in interface NavigableMap

tailMap

public SortedMap tailMap(Object fromKey)
Specified by:
tailMap in interface ConcurrentNavigableMap
tailMap in interface NavigableMap

tailMap

public NavigableMap tailMap(Object fromKey,
                            boolean inclusive)
Specified by:
tailMap in interface ConcurrentNavigableMap
tailMap in interface NavigableMap

values

public Collection values()
Returns a Collection view of the values contained in this map. The collection's iterator returns the values in ascending order of the corresponding keys. The collection is backed by the map, so changes to the map are reflected in the collection, and vice-versa. The collection supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Collection.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.

The view's iterator is a "weakly consistent" iterator that will never throw java.util.ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.