com.googlecode.concurrenttrees.radix
Class ConcurrentRadixTree<O>

java.lang.Object
  com.googlecode.concurrenttrees.radix.ConcurrentRadixTree<O>

All Implemented Interfaces:

PrettyPrintable, RadixTree<O>

public class ConcurrentRadixTree<O>
extends Object
implements RadixTree<O>, PrettyPrintable

An implementation of RadixTree which supports lock-free concurrent reads, and allows items to be added to and to be removed from the tree atomically by background thread(s), without blocking reads.

Unlike reads, writes require locking of the tree (locking out other writing threads only; reading threads are never blocked). Currently write locks are coarse-grained; in fact they are tree-level. In future branch-level write locks might be added, but the current implementation is targeted at high concurrency read-mostly use cases.

Author:

Niall Gallagher

Nested Class Summary

static class	ConcurrentRadixTree.KeyValuePairImpl<O> Implementation of the KeyValuePair interface.
protected static class	ConcurrentRadixTree.NodeKeyPair Encapsulates a node and its associated key.

Field Summary

protected Node

root

Constructor Summary

ConcurrentRadixTree(NodeFactory nodeFactory)
Creates a new ConcurrentRadixTree which will use the given NodeFactory to create nodes.

ConcurrentRadixTree(NodeFactory nodeFactory, boolean restrictConcurrency)
Creates a new ConcurrentRadixTree which will use the given NodeFactory to create nodes.

Method Summary

protected void	acquireReadLockIfNecessary()
protected void	acquireWriteLock()
Iterable<CharSequence>	getClosestKeys(CharSequence candidate) Returns a lazy iterable which returns the set of keys in the tree which are the closest match for the given candidate key.
Iterable<CharSequence>	getKeysStartingWith(CharSequence prefix) Returns a lazy iterable which returns the set of keys in the tree which start with the given prefix.
Iterable<KeyValuePair<O>>	getKeyValuePairsForClosestKeys(CharSequence candidate) Returns a lazy iterable which returns the set of KeyValuePairs for keys and their associated values in the tree which are the closest match for the given candidate key.
Iterable<KeyValuePair<O>>	getKeyValuePairsForKeysStartingWith(CharSequence prefix) Returns a lazy iterable which returns the set of KeyValuePairs for keys and their associated values in the tree, where the keys start with the given prefix.
Node	getNode()
O	getValueForExactKey(CharSequence key) Returns the value associated with the given key (exact match), or returns null if no such value is associated with the key.
Iterable<O>	getValuesForClosestKeys(CharSequence candidate) Returns a lazy iterable which returns the set of values associated with keys in the tree which are the closest match for the given candidate key.
Iterable<O>	getValuesForKeysStartingWith(CharSequence prefix) Returns a lazy iterable which returns the set of values associated with keys in the tree which start with the given prefix.
protected Iterable<ConcurrentRadixTree.NodeKeyPair>	lazyTraverseDescendants(CharSequence startKey, Node startNode) Traverses the tree using depth-first, preordered traversal, starting at the given node, using lazy evaluation such that the next node is only determined when next() is called on the iterator returned.
O	put(CharSequence key, O value) Associates the given value with the given key; replacing any previous value associated with the key.
O	putIfAbsent(CharSequence key, O value) If a value is not already associated with the given key in the tree, associates the given value with the key; otherwise if an existing value is already associated, returns the existing value and does not overwrite it.
protected void	releaseReadLockIfNecessary()
protected void	releaseWriteLock()
boolean	remove(CharSequence key) Removes the value associated with the given key (exact match).
int	size() Counts the number of keys/values stored in the tree.
protected CharSequence	transformKeyForResult(CharSequence rawKey) A hook method which may be overridden by subclasses, to transform a key just before it is returned to the application, for example by the getKeysStartingWith(CharSequence) or the getKeyValuePairsForKeysStartingWith(CharSequence) methods.

Methods inherited from class java.lang.Object

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

Field Detail

root

protected volatile Node root

Constructor Detail

ConcurrentRadixTree

public ConcurrentRadixTree(NodeFactory nodeFactory)

Creates a new ConcurrentRadixTree which will use the given NodeFactory to create nodes.

Parameters:

nodeFactory - An object which creates Node objects on-demand, and which might return node implementations optimized for storing the values supplied to it for the creation of each node

ConcurrentRadixTree

public ConcurrentRadixTree(NodeFactory nodeFactory,
                           boolean restrictConcurrency)

Creates a new ConcurrentRadixTree which will use the given NodeFactory to create nodes.

Parameters:

nodeFactory - An object which creates Node objects on-demand, and which might return node implementations optimized for storing the values supplied to it for the creation of each node

restrictConcurrency - If true, configures use of a ReadWriteLock allowing concurrent reads, except when writes are being performed by other threads, in which case writes block all reads; if false, configures lock-free reads; allows concurrent non-blocking reads, even if writes are being performed by other threads

Method Detail

acquireWriteLock

protected void acquireWriteLock()

releaseWriteLock

protected void releaseWriteLock()

acquireReadLockIfNecessary

protected void acquireReadLockIfNecessary()

releaseReadLockIfNecessary

protected void releaseReadLockIfNecessary()

put

public O put(CharSequence key,
             O value)

Associates the given value with the given key; replacing any previous value associated with the key. Returns the previous value associated with the key, if any.

This operation is performed atomically.

Specified by:

put in interface RadixTree<O>

Parameters:

key - The key with which the specified value should be associated

value - The value to associate with the key, which cannot be null

Returns:

The previous value associated with the key, if there was one, otherwise null

putIfAbsent

public O putIfAbsent(CharSequence key,
                     O value)

If a value is not already associated with the given key in the tree, associates the given value with the key; otherwise if an existing value is already associated, returns the existing value and does not overwrite it.

This operation is performed atomically.

Specified by:

putIfAbsent in interface RadixTree<O>

Parameters:

key - The key with which the specified value should be associated

value - The value to associate with the key, which cannot be null

Returns:

The existing value associated with the key, if there was one; otherwise null in which case the new value was successfully associated

getValueForExactKey

public O getValueForExactKey(CharSequence key)

Returns the value associated with the given key (exact match), or returns null if no such value is associated with the key.

Specified by:

getValueForExactKey in interface RadixTree<O>

Parameters:

key - The key with which a sought value might be associated

Returns:

The value associated with the given key (exact match), or null if no value was associated with the key

getKeysStartingWith

public Iterable<CharSequence> getKeysStartingWith(CharSequence prefix)

Returns a lazy iterable which returns the set of keys in the tree which start with the given prefix.

This is inclusive - if the given prefix is an exact match for a key in the tree, that key is also returned.

Specified by:

getKeysStartingWith in interface RadixTree<O>

Parameters:

prefix - A prefix of sought keys in the tree

Returns:

The set of keys in the tree which start with the given prefix, inclusive

getValuesForKeysStartingWith

public Iterable<O> getValuesForKeysStartingWith(CharSequence prefix)

Returns a lazy iterable which returns the set of values associated with keys in the tree which start with the given prefix.

This is inclusive - if the given prefix is an exact match for a key in the tree, the value associated with that key is also returned.

Note that although the same value might originally have been associated with multiple keys, the set returned does not contain duplicates (as determined by the value objects' implementation of #equals(Object)).

Specified by:

getValuesForKeysStartingWith in interface RadixTree<O>

Parameters:

prefix - A prefix of keys in the tree for which associated values are sought

Returns:

The set of values associated with keys in the tree which start with the given prefix, inclusive

getKeyValuePairsForKeysStartingWith

public Iterable<KeyValuePair<O>> getKeyValuePairsForKeysStartingWith(CharSequence prefix)

Returns a lazy iterable which returns the set of KeyValuePairs for keys and their associated values in the tree, where the keys start with the given prefix.

This is inclusive - if the given prefix is an exact match for a key in the tree, the KeyValuePair for that key is also returned.

Specified by:

getKeyValuePairsForKeysStartingWith in interface RadixTree<O>

Parameters:

prefix - A prefix of keys in the tree for which associated KeyValuePairs are sought

Returns:

The set of KeyValuePairs for keys in the tree which start with the given prefix, inclusive

remove

public boolean remove(CharSequence key)

Removes the value associated with the given key (exact match). If no value is associated with the key, does nothing.

Specified by:

remove in interface RadixTree<O>

Parameters:

key - The key for which an associated value should be removed

Returns:

True if a value was removed (and therefore was associated with the key), false if no value was associated/removed

getClosestKeys

public Iterable<CharSequence> getClosestKeys(CharSequence candidate)

Returns a lazy iterable which returns the set of keys in the tree which are the closest match for the given candidate key.

Example:
Tree contains: Ford Focus, Ford Mondeo, BMW M3
getClosestKeys("Ford F150") -> returns Ford Focus, Ford Mondeo

This is inclusive - if the given candidate is an exact match for a key in the tree, that key is also returned.

Specified by:

getClosestKeys in interface RadixTree<O>

Parameters:

candidate - A candidate key

Returns:

The set of keys in the tree which most closely match the candidate key, inclusive

getValuesForClosestKeys

public Iterable<O> getValuesForClosestKeys(CharSequence candidate)

Returns a lazy iterable which returns the set of values associated with keys in the tree which are the closest match for the given candidate key.

See {#getClosestKeys} for more details.

Specified by:

getValuesForClosestKeys in interface RadixTree<O>

Parameters:

candidate - A candidate key

Returns:

The set of values associated with keys in the tree which most closely match the candidate key, inclusive

getKeyValuePairsForClosestKeys

public Iterable<KeyValuePair<O>> getKeyValuePairsForClosestKeys(CharSequence candidate)

Returns a lazy iterable which returns the set of KeyValuePairs for keys and their associated values in the tree which are the closest match for the given candidate key.

See {#getClosestKeys} for more details.

Specified by:

getKeyValuePairsForClosestKeys in interface RadixTree<O>

Parameters:

candidate - A candidate key

Returns:

The set of KeyValuePairs for keys and their associated values in the tree which most closely match the candidate key, inclusive

size

public int size()

Counts the number of keys/values stored in the tree.

In the current implementation, this is an expensive operation, having O(n) time complexity.

Specified by:

size in interface RadixTree<O>

Returns:

The number of keys/values stored in the tree

lazyTraverseDescendants

protected Iterable<ConcurrentRadixTree.NodeKeyPair> lazyTraverseDescendants(CharSequence startKey,
                                                                            Node startNode)

Traverses the tree using depth-first, preordered traversal, starting at the given node, using lazy evaluation such that the next node is only determined when next() is called on the iterator returned. The traversal algorithm uses iteration instead of recursion to allow deep trees to be traversed without requiring large JVM stack sizes.

Each node that is encountered is returned from the iterator along with a key associated with that node, in a NodeKeyPair object. The key will be prefixed by the given start key, and will be generated by appending to the start key the edges traversed along the path to that node from the start node.

Parameters:

startKey - The key which matches the given start node

startNode - The start node

Returns:

An iterator which when iterated traverses the tree using depth-first, preordered traversal, starting at the given start node

transformKeyForResult

protected CharSequence transformKeyForResult(CharSequence rawKey)

A hook method which may be overridden by subclasses, to transform a key just before it is returned to the application, for example by the getKeysStartingWith(CharSequence) or the getKeyValuePairsForKeysStartingWith(CharSequence) methods.

This hook is expected to be used by ReversedRadixTree implementations, where keys are stored in the tree in reverse order but results should be returned in normal order.

This default implementation simply returns the given key unmodified.

Parameters:

rawKey - The raw key as stored in the tree

Returns:

A transformed version of the key

getNode

public Node getNode()

Specified by:

getNode in interface PrettyPrintable