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Concurrent Radix Trees and Concurrent Suffix Trees for Java.
/**
* Copyright 2012-2013 Niall Gallagher
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.googlecode.concurrenttrees.radix;
import com.googlecode.concurrenttrees.common.CharSequences;
import com.googlecode.concurrenttrees.common.KeyValuePair;
import com.googlecode.concurrenttrees.common.LazyIterator;
import com.googlecode.concurrenttrees.radix.node.Node;
import com.googlecode.concurrenttrees.radix.node.NodeFactory;
import com.googlecode.concurrenttrees.radix.node.util.PrettyPrintable;
import java.io.Serializable;
import java.util.*;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import static com.googlecode.concurrenttrees.radix.ConcurrentRadixTree.SearchResult.Classification;
/**
* An implementation of {@link 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
*/
public class ConcurrentRadixTree implements RadixTree, PrettyPrintable, Serializable {
private final NodeFactory nodeFactory;
protected volatile Node root;
// Write operations acquire write lock, read operations are lock-free.
private final Lock writeLock = new ReentrantLock();
/**
* Creates a new {@link ConcurrentRadixTree} which will use the given {@link NodeFactory} to create nodes.
*
* @param nodeFactory An object which creates {@link Node} objects on-demand, and which might return node
* implementations optimized for storing the values supplied to it for the creation of each node
*/
public ConcurrentRadixTree(NodeFactory nodeFactory) {
this.nodeFactory = nodeFactory;
@SuppressWarnings({"NullableProblems", "UnnecessaryLocalVariable"})
Node rootNode = nodeFactory.createNode("", null, Collections.emptyList(), true);
this.root = rootNode;
}
// ------------- Helper methods for serializing writes -------------
protected void acquireWriteLock() {
writeLock.lock();
}
protected void releaseWriteLock() {
writeLock.unlock();
}
// ------------- Public API methods -------------
/**
* {@inheritDoc}
*/
@Override
public O put(CharSequence key, O value) {
@SuppressWarnings({"unchecked", "UnnecessaryLocalVariable"})
O existingValue = (O) putInternal(key, value, true); // putInternal acquires write lock
return existingValue;
}
/**
* {@inheritDoc}
*/
@Override
public O putIfAbsent(CharSequence key, O value) {
@SuppressWarnings({"unchecked", "UnnecessaryLocalVariable"})
O existingValue = (O) putInternal(key, value, false); // putInternal acquires write lock
return existingValue;
}
/**
* {@inheritDoc}
*/
@Override
public O getValueForExactKey(CharSequence key) {
SearchResult searchResult = searchTree(key);
if (searchResult.classification.equals(SearchResult.Classification.EXACT_MATCH)) {
@SuppressWarnings({"unchecked", "UnnecessaryLocalVariable"})
O value = (O) searchResult.nodeFound.getValue();
return value;
}
return null;
}
/**
* {@inheritDoc}
*/
@Override
public Iterable getKeysStartingWith(CharSequence prefix) {
SearchResult searchResult = searchTree(prefix);
Classification classification = searchResult.classification;
switch (classification) {
case EXACT_MATCH: {
return getDescendantKeys(prefix, searchResult.nodeFound);
}
case KEY_ENDS_MID_EDGE: {
// Append the remaining characters of the edge to the key.
// For example if we searched for CO, but first matching node was COFFEE,
// the key associated with the first node should be COFFEE...
CharSequence edgeSuffix = CharSequences.getSuffix(searchResult.nodeFound.getIncomingEdge(), searchResult.charsMatchedInNodeFound);
prefix = CharSequences.concatenate(prefix, edgeSuffix);
return getDescendantKeys(prefix, searchResult.nodeFound);
}
default: {
// Incomplete match means key is not a prefix of any node...
return Collections.emptySet();
}
}
}
/**
* {@inheritDoc}
*/
@Override
public Iterable getValuesForKeysStartingWith(CharSequence prefix) {
SearchResult searchResult = searchTree(prefix);
Classification classification = searchResult.classification;
switch (classification) {
case EXACT_MATCH: {
return getDescendantValues(prefix, searchResult.nodeFound);
}
case KEY_ENDS_MID_EDGE: {
// Append the remaining characters of the edge to the key.
// For example if we searched for CO, but first matching node was COFFEE,
// the key associated with the first node should be COFFEE...
CharSequence edgeSuffix = CharSequences.getSuffix(searchResult.nodeFound.getIncomingEdge(), searchResult.charsMatchedInNodeFound);
prefix = CharSequences.concatenate(prefix, edgeSuffix);
return getDescendantValues(prefix, searchResult.nodeFound);
}
default: {
// Incomplete match means key is not a prefix of any node...
return Collections.emptySet();
}
}
}
/**
* {@inheritDoc}
*/
@Override
public Iterable> getKeyValuePairsForKeysStartingWith(CharSequence prefix) {
SearchResult searchResult = searchTree(prefix);
Classification classification = searchResult.classification;
switch (classification) {
case EXACT_MATCH: {
return getDescendantKeyValuePairs(prefix, searchResult.nodeFound);
}
case KEY_ENDS_MID_EDGE: {
// Append the remaining characters of the edge to the key.
// For example if we searched for CO, but first matching node was COFFEE,
// the key associated with the first node should be COFFEE...
CharSequence edgeSuffix = CharSequences.getSuffix(searchResult.nodeFound.getIncomingEdge(), searchResult.charsMatchedInNodeFound);
prefix = CharSequences.concatenate(prefix, edgeSuffix);
return getDescendantKeyValuePairs(prefix, searchResult.nodeFound);
}
default: {
// Incomplete match means key is not a prefix of any node...
return Collections.emptySet();
}
}
}
/**
* {@inheritDoc}
*/
@Override
public boolean remove(CharSequence key) {
if (key == null) {
throw new IllegalArgumentException("The key argument was null");
}
acquireWriteLock();
try {
SearchResult searchResult = searchTree(key);
SearchResult.Classification classification = searchResult.classification;
switch (classification) {
case EXACT_MATCH: {
if (searchResult.nodeFound.getValue() == null) {
// This node was created automatically as a split between two branches (implicit node).
// No need to remove it...
return false;
}
// Proceed with deleting the node...
List childEdges = searchResult.nodeFound.getOutgoingEdges();
if (childEdges.size() > 1) {
// This node has more than one child, so if we delete the value from this node, we still need
// to leave a similar node in place to act as the split between the child edges.
// Just delete the value associated with this node.
// -> Clone this node without its value, preserving its child nodes...
@SuppressWarnings({"NullableProblems"})
Node cloned = nodeFactory.createNode(searchResult.nodeFound.getIncomingEdge(), null, searchResult.nodeFound.getOutgoingEdges(), false);
// Re-add the replacement node to the parent...
searchResult.parentNode.updateOutgoingEdge(cloned);
}
else if (childEdges.size() == 1) {
// Node has one child edge.
// Create a new node which is the concatenation of the edges from this node and its child,
// and which has the outgoing edges of the child and the value from the child.
Node child = childEdges.get(0);
CharSequence concatenatedEdges = CharSequences.concatenate(searchResult.nodeFound.getIncomingEdge(), child.getIncomingEdge());
Node mergedNode = nodeFactory.createNode(concatenatedEdges, child.getValue(), child.getOutgoingEdges(), false);
// Re-add the merged node to the parent...
searchResult.parentNode.updateOutgoingEdge(mergedNode);
}
else {
// Node has no children. Delete this node from its parent,
// which involves re-creating the parent rather than simply updating its child edge
// (this is why we need parentNodesParent).
// However if this would leave the parent with only one remaining child edge,
// and the parent itself has no value (is a split node), and the parent is not the root node
// (a special case which we never merge), then we also need to merge the parent with its
// remaining child.
List currentEdgesFromParent = searchResult.parentNode.getOutgoingEdges();
// Create a list of the outgoing edges of the parent which will remain
// if we remove this child...
// Use a non-resizable list, as a sanity check to force ArrayIndexOutOfBounds...
List newEdgesOfParent = Arrays.asList(new Node[searchResult.parentNode.getOutgoingEdges().size() - 1]);
for (int i = 0, added = 0, numParentEdges = currentEdgesFromParent.size(); i < numParentEdges; i++) {
Node node = currentEdgesFromParent.get(i);
if (node != searchResult.nodeFound) {
newEdgesOfParent.set(added++, node);
}
}
// Note the parent might actually be the root node (which we should never merge)...
boolean parentIsRoot = (searchResult.parentNode == root);
Node newParent;
if (newEdgesOfParent.size() == 1 && searchResult.parentNode.getValue() == null && !parentIsRoot) {
// Parent is a non-root split node with only one remaining child, which can now be merged.
Node parentsRemainingChild = newEdgesOfParent.get(0);
// Merge the parent with its only remaining child...
CharSequence concatenatedEdges = CharSequences.concatenate(searchResult.parentNode.getIncomingEdge(), parentsRemainingChild.getIncomingEdge());
newParent = nodeFactory.createNode(concatenatedEdges, parentsRemainingChild.getValue(), parentsRemainingChild.getOutgoingEdges(), parentIsRoot);
}
else {
// Parent is a node which either has a value of its own, has more than one remaining
// child, or is actually the root node (we never merge the root node).
// Create new parent node which is the same as is currently just without the edge to the
// node being deleted...
newParent = nodeFactory.createNode(searchResult.parentNode.getIncomingEdge(), searchResult.parentNode.getValue(), newEdgesOfParent, parentIsRoot);
}
// Re-add the parent node to its parent...
if (parentIsRoot) {
// Replace the root node...
this.root = newParent;
}
else {
// Re-add the parent node to its parent...
searchResult.parentNodesParent.updateOutgoingEdge(newParent);
}
}
return true;
}
default: {
return false;
}
}
}
finally {
releaseWriteLock();
}
}
/**
* {@inheritDoc}
*/
@Override
public Iterable getClosestKeys(CharSequence candidate) {
SearchResult searchResult = searchTree(candidate);
Classification classification = searchResult.classification;
switch (classification) {
case EXACT_MATCH: {
return getDescendantKeys(candidate, searchResult.nodeFound);
}
case KEY_ENDS_MID_EDGE: {
// Append the remaining characters of the edge to the key.
// For example if we searched for CO, but first matching node was COFFEE,
// the key associated with the first node should be COFFEE...
CharSequence edgeSuffix = CharSequences.getSuffix(searchResult.nodeFound.getIncomingEdge(), searchResult.charsMatchedInNodeFound);
candidate = CharSequences.concatenate(candidate, edgeSuffix);
return getDescendantKeys(candidate, searchResult.nodeFound);
}
case INCOMPLETE_MATCH_TO_MIDDLE_OF_EDGE: {
// Example: if we searched for CX, but deepest matching node was CO,
// the results should include node CO and its descendants...
CharSequence keyOfParentNode = CharSequences.getPrefix(candidate, searchResult.charsMatched - searchResult.charsMatchedInNodeFound);
CharSequence keyOfNodeFound = CharSequences.concatenate(keyOfParentNode, searchResult.nodeFound.getIncomingEdge());
return getDescendantKeys(keyOfNodeFound, searchResult.nodeFound);
}
case INCOMPLETE_MATCH_TO_END_OF_EDGE: {
if (searchResult.charsMatched == 0) {
// Closest match is the root node, we don't consider this a match for anything...
break;
}
// Example: if we searched for COFFEE, but deepest matching node was CO,
// the results should include node CO and its descendants...
CharSequence keyOfNodeFound = CharSequences.getPrefix(candidate, searchResult.charsMatched);
return getDescendantKeys(keyOfNodeFound, searchResult.nodeFound);
}
}
return Collections.emptySet();
}
/**
* {@inheritDoc}
*/
@Override
public Iterable getValuesForClosestKeys(CharSequence candidate) {
SearchResult searchResult = searchTree(candidate);
Classification classification = searchResult.classification;
switch (classification) {
case EXACT_MATCH: {
return getDescendantValues(candidate, searchResult.nodeFound);
}
case KEY_ENDS_MID_EDGE: {
// Append the remaining characters of the edge to the key.
// For example if we searched for CO, but first matching node was COFFEE,
// the key associated with the first node should be COFFEE...
CharSequence edgeSuffix = CharSequences.getSuffix(searchResult.nodeFound.getIncomingEdge(), searchResult.charsMatchedInNodeFound);
candidate = CharSequences.concatenate(candidate, edgeSuffix);
return getDescendantValues(candidate, searchResult.nodeFound);
}
case INCOMPLETE_MATCH_TO_MIDDLE_OF_EDGE: {
// Example: if we searched for CX, but deepest matching node was CO,
// the results should include node CO and its descendants...
CharSequence keyOfParentNode = CharSequences.getPrefix(candidate, searchResult.charsMatched - searchResult.charsMatchedInNodeFound);
CharSequence keyOfNodeFound = CharSequences.concatenate(keyOfParentNode, searchResult.nodeFound.getIncomingEdge());
return getDescendantValues(keyOfNodeFound, searchResult.nodeFound);
}
case INCOMPLETE_MATCH_TO_END_OF_EDGE: {
if (searchResult.charsMatched == 0) {
// Closest match is the root node, we don't consider this a match for anything...
break;
}
// Example: if we searched for COFFEE, but deepest matching node was CO,
// the results should include node CO and its descendants...
CharSequence keyOfNodeFound = CharSequences.getPrefix(candidate, searchResult.charsMatched);
return getDescendantValues(keyOfNodeFound, searchResult.nodeFound);
}
}
return Collections.emptySet();
}
/**
* {@inheritDoc}
*/
@Override
public Iterable> getKeyValuePairsForClosestKeys(CharSequence candidate) {
SearchResult searchResult = searchTree(candidate);
Classification classification = searchResult.classification;
switch (classification) {
case EXACT_MATCH: {
return getDescendantKeyValuePairs(candidate, searchResult.nodeFound);
}
case KEY_ENDS_MID_EDGE: {
// Append the remaining characters of the edge to the key.
// For example if we searched for CO, but first matching node was COFFEE,
// the key associated with the first node should be COFFEE...
CharSequence edgeSuffix = CharSequences.getSuffix(searchResult.nodeFound.getIncomingEdge(), searchResult.charsMatchedInNodeFound);
candidate = CharSequences.concatenate(candidate, edgeSuffix);
return getDescendantKeyValuePairs(candidate, searchResult.nodeFound);
}
case INCOMPLETE_MATCH_TO_MIDDLE_OF_EDGE: {
// Example: if we searched for CX, but deepest matching node was CO,
// the results should include node CO and its descendants...
CharSequence keyOfParentNode = CharSequences.getPrefix(candidate, searchResult.charsMatched - searchResult.charsMatchedInNodeFound);
CharSequence keyOfNodeFound = CharSequences.concatenate(keyOfParentNode, searchResult.nodeFound.getIncomingEdge());
return getDescendantKeyValuePairs(keyOfNodeFound, searchResult.nodeFound);
}
case INCOMPLETE_MATCH_TO_END_OF_EDGE: {
if (searchResult.charsMatched == 0) {
// Closest match is the root node, we don't consider this a match for anything...
break;
}
// Example: if we searched for COFFEE, but deepest matching node was CO,
// the results should include node CO and its descendants...
CharSequence keyOfNodeFound = CharSequences.getPrefix(candidate, searchResult.charsMatched);
return getDescendantKeyValuePairs(keyOfNodeFound, searchResult.nodeFound);
}
}
return Collections.emptySet();
}
/**
* {@inheritDoc}
*/
@Override
public int size() {
Deque stack = new LinkedList();
stack.push(this.root);
int count = 0;
while (true) {
if (stack.isEmpty()) {
return count;
}
Node current = stack.pop();
stack.addAll(current.getOutgoingEdges());
if (current.getValue() != null) {
count++;
}
}
}
// ------------- Helper method for put() -------------
/**
* Atomically adds the given value to the tree, creating a node for the value as necessary. If the value is already
* stored for the same key, either overwrites the existing value, or simply returns the existing value, depending
* on the given value of the overwrite flag.
*
* @param key The key against which the value should be stored
* @param value The value to store against the key
* @param overwrite If true, should replace any existing value, if false should not replace any existing value
* @return The existing value for this key, if there was one, otherwise null
*/
Object putInternal(CharSequence key, Object value, boolean overwrite) {
if (key == null) {
throw new IllegalArgumentException("The key argument was null");
}
if (key.length() == 0) {
throw new IllegalArgumentException("The key argument was zero-length");
}
if (value == null) {
throw new IllegalArgumentException("The value argument was null");
}
acquireWriteLock();
try {
// Note we search the tree here after we have acquired the write lock...
SearchResult searchResult = searchTree(key);
SearchResult.Classification classification = searchResult.classification;
switch (classification) {
case EXACT_MATCH: {
// Search found an exact match for all edges leading to this node.
// -> Add or update the value in the node found, by replacing
// the existing node with a new node containing the value...
// First check if existing node has a value, and if we are allowed to overwrite it.
// Return early without overwriting if necessary...
Object existingValue = searchResult.nodeFound.getValue();
if (!overwrite && existingValue != null) {
return existingValue;
}
// Create a replacement for the existing node containing the new value...
Node replacementNode = nodeFactory.createNode(searchResult.nodeFound.getIncomingEdge(), value, searchResult.nodeFound.getOutgoingEdges(), false);
searchResult.parentNode.updateOutgoingEdge(replacementNode);
// Return the existing value...
return existingValue;
}
case KEY_ENDS_MID_EDGE: {
// Search ran out of characters from the key while in the middle of an edge in the node.
// -> Split the node in two: Create a new parent node storing the new value,
// and a new child node holding the original value and edges from the existing node...
CharSequence keyCharsFromStartOfNodeFound = key.subSequence(searchResult.charsMatched - searchResult.charsMatchedInNodeFound, key.length());
CharSequence commonPrefix = CharSequences.getCommonPrefix(keyCharsFromStartOfNodeFound, searchResult.nodeFound.getIncomingEdge());
CharSequence suffixFromExistingEdge = CharSequences.subtractPrefix(searchResult.nodeFound.getIncomingEdge(), commonPrefix);
// Create new nodes...
Node newChild = nodeFactory.createNode(suffixFromExistingEdge, searchResult.nodeFound.getValue(), searchResult.nodeFound.getOutgoingEdges(), false);
Node newParent = nodeFactory.createNode(commonPrefix, value, Arrays.asList(newChild), false);
// Add the new parent to the parent of the node being replaced (replacing the existing node)...
searchResult.parentNode.updateOutgoingEdge(newParent);
// Return null for the existing value...
return null;
}
case INCOMPLETE_MATCH_TO_END_OF_EDGE: {
// Search found a difference in characters between the key and the start of all child edges leaving the
// node, the key still has trailing unmatched characters.
// -> Add a new child to the node, containing the trailing characters from the key.
// NOTE: this is the only branch which allows an edge to be added to the root.
// (Root node's own edge is "" empty string, so is considered a prefixing edge of every key)
// Create a new child node containing the trailing characters...
CharSequence keySuffix = key.subSequence(searchResult.charsMatched, key.length());
Node newChild = nodeFactory.createNode(keySuffix, value, Collections.emptyList(), false);
// Clone the current node adding the new child...
List edges = new ArrayList(searchResult.nodeFound.getOutgoingEdges().size() + 1);
edges.addAll(searchResult.nodeFound.getOutgoingEdges());
edges.add(newChild);
Node clonedNode = nodeFactory.createNode(searchResult.nodeFound.getIncomingEdge(), searchResult.nodeFound.getValue(), edges, searchResult.nodeFound == root);
// Re-add the cloned node to its parent node...
if (searchResult.nodeFound == root) {
this.root = clonedNode;
}
else {
searchResult.parentNode.updateOutgoingEdge(clonedNode);
}
// Return null for the existing value...
return null;
}
case INCOMPLETE_MATCH_TO_MIDDLE_OF_EDGE: {
// Search found a difference in characters between the key and the characters in the middle of the
// edge in the current node, and the key still has trailing unmatched characters.
// -> Split the node in three:
// Let's call node found: NF
// (1) Create a new node N1 containing the unmatched characters from the rest of the key, and the
// value supplied to this method
// (2) Create a new node N2 containing the unmatched characters from the rest of the edge in NF, and
// copy the original edges and the value from NF unmodified into N2
// (3) Create a new node N3, which will be the split node, containing the matched characters from
// the key and the edge, and add N1 and N2 as child nodes of N3
// (4) Re-add N3 to the parent node of NF, effectively replacing NF in the tree
CharSequence keyCharsFromStartOfNodeFound = key.subSequence(searchResult.charsMatched - searchResult.charsMatchedInNodeFound, key.length());
CharSequence commonPrefix = CharSequences.getCommonPrefix(keyCharsFromStartOfNodeFound, searchResult.nodeFound.getIncomingEdge());
CharSequence suffixFromExistingEdge = CharSequences.subtractPrefix(searchResult.nodeFound.getIncomingEdge(), commonPrefix);
CharSequence suffixFromKey = key.subSequence(searchResult.charsMatched, key.length());
// Create new nodes...
Node n1 = nodeFactory.createNode(suffixFromKey, value, Collections.emptyList(), false);
Node n2 = nodeFactory.createNode(suffixFromExistingEdge, searchResult.nodeFound.getValue(), searchResult.nodeFound.getOutgoingEdges(), false);
@SuppressWarnings({"NullableProblems"})
Node n3 = nodeFactory.createNode(commonPrefix, null, Arrays.asList(n1, n2), false);
searchResult.parentNode.updateOutgoingEdge(n3);
// Return null for the existing value...
return null;
}
default: {
// This is a safeguard against a new enum constant being added in future.
throw new IllegalStateException("Unexpected classification for search result: " + searchResult);
}
}
}
finally {
releaseWriteLock();
}
}
// ------------- Helper method for finding descendants of a given node -------------
/**
* Returns a lazy iterable which will return {@link CharSequence} keys for which the given key is a prefix.
* The results inherently will not contain duplicates (duplicate keys cannot exist in the tree).
*
* Note that this method internally converts {@link CharSequence}s to {@link String}s, to avoid set equality issues,
* because equals() and hashCode() are not specified by the CharSequence API contract.
*/
@SuppressWarnings({"JavaDoc"})
Iterable getDescendantKeys(final CharSequence startKey, final Node startNode) {
return new Iterable () {
@Override
public Iterator iterator() {
return new LazyIterator() {
Iterator descendantNodes = lazyTraverseDescendants(startKey, startNode).iterator();
@Override
protected CharSequence computeNext() {
// Traverse to the next matching node in the tree and return its key and value...
while (descendantNodes.hasNext()) {
NodeKeyPair nodeKeyPair = descendantNodes.next();
Object value = nodeKeyPair.node.getValue();
if (value != null) {
// Dealing with a node explicitly added to tree (rather than an automatically-added split node).
// Call the transformKeyForResult method to allow key to be transformed before returning to client.
// Used by subclasses such as ReversedRadixTree implementations...
CharSequence optionallyTransformedKey = transformKeyForResult(nodeKeyPair.key);
// -> Convert the CharSequence to a String before returning, to avoid set equality issues,
// because equals() and hashCode() is not specified by the CharSequence API contract...
return CharSequences.toString(optionallyTransformedKey);
}
}
// Finished traversing the tree, no more matching nodes to return...
return endOfData();
}
};
}
};
}
/**
* Returns a lazy iterable which will return values which are associated with keys in the tree for which
* the given key is a prefix.
*/
@SuppressWarnings({"JavaDoc"})
Iterable getDescendantValues(final CharSequence startKey, final Node startNode) {
return new Iterable () {
@Override
public Iterator iterator() {
return new LazyIterator() {
Iterator descendantNodes = lazyTraverseDescendants(startKey, startNode).iterator();
@Override
protected O computeNext() {
// Traverse to the next matching node in the tree and return its key and value...
while (descendantNodes.hasNext()) {
NodeKeyPair nodeKeyPair = descendantNodes.next();
Object value = nodeKeyPair.node.getValue();
if (value != null) {
// Dealing with a node explicitly added to tree (rather than an automatically-added split node).
// We have to cast to generic type here, because Node objects are not generically typed.
// Background: Node objects are not generically typed, because arrays can't be generically typed,
// and we use arrays in nodes. We choose to cast here (in wrapper logic around the tree) rather than
// pollute the already-complex tree manipulation logic with casts.
@SuppressWarnings({"unchecked", "UnnecessaryLocalVariable"})
O valueTyped = (O)value;
return valueTyped;
}
}
// Finished traversing the tree, no more matching nodes to return...
return endOfData();
}
};
}
};
}
/**
* Returns a lazy iterable which will return {@link KeyValuePair} objects each containing a key and a value,
* for which the given key is a prefix of the key in the {@link KeyValuePair}. These results inherently will not
* contain duplicates (duplicate keys cannot exist in the tree).
*
* Note that this method internally converts {@link CharSequence}s to {@link String}s, to avoid set equality issues,
* because equals() and hashCode() are not specified by the CharSequence API contract.
*/
@SuppressWarnings({"JavaDoc"})
Iterable> getDescendantKeyValuePairs(final CharSequence startKey, final Node startNode) {
return new Iterable> () {
@Override
public Iterator> iterator() {
return new LazyIterator>() {
Iterator descendantNodes = lazyTraverseDescendants(startKey, startNode).iterator();
@Override
protected KeyValuePair computeNext() {
// Traverse to the next matching node in the tree and return its key and value...
while (descendantNodes.hasNext()) {
NodeKeyPair nodeKeyPair = descendantNodes.next();
Object value = nodeKeyPair.node.getValue();
if (value != null) {
// Dealing with a node explicitly added to tree (rather than an automatically-added split node).
// Call the transformKeyForResult method to allow key to be transformed before returning to client.
// Used by subclasses such as ReversedRadixTree implementations...
CharSequence optionallyTransformedKey = transformKeyForResult(nodeKeyPair.key);
// -> Convert the CharSequence to a String before returning, to avoid set equality issues,
// because equals() and hashCode() is not specified by the CharSequence API contract...
String keyString = CharSequences.toString(optionallyTransformedKey);
return new KeyValuePairImpl(keyString, value);
}
}
// Finished traversing the tree, no more matching nodes to return...
return endOfData();
}
};
}
};
}
/**
* Implementation of the {@link KeyValuePair} interface.
*/
public static class KeyValuePairImpl implements KeyValuePair {
final String key;
final O value;
/**
* Constructor.
*
* Implementation node: This constructor currently requires the key to be supplied as a {@link String}
* - this is to allow reliable testing of object equality; the alternative {@link CharSequence}
* does not specify a contract for {@link Object#equals(Object)}.
*
* @param key The key as a string
* @param value The value
*/
public KeyValuePairImpl(String key, Object value) {
this.key = key;
// We have to cast to generic type here, because Node objects are not generically typed.
// Background: Node objects are not generically typed, because arrays can't be generically typed,
// and we use arrays in nodes. We choose to cast here (in wrapper logic around the tree) rather than
// pollute the already-complex tree manipulation logic with casts.
@SuppressWarnings({"unchecked", "UnnecessaryLocalVariable"})
O valueTyped = (O)value;
this.value = valueTyped;
}
/**
* {@inheritDoc}
*/
@Override
public CharSequence getKey() {
return key;
}
/**
* {@inheritDoc}
*/
@Override
public O getValue() {
return value;
}
/**
* {@inheritDoc}
*/
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
KeyValuePairImpl that = (KeyValuePairImpl) o;
return key.equals(that.key);
}
/**
* {@inheritDoc}
*/
@Override
public int hashCode() {
return key.hashCode();
}
/**
* {@inheritDoc}
*/
@Override
public String toString() {
return "(" + key + ", " + value + ")";
}
}
/**
* 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.
*
* @param startKey The key which matches the given start node
* @param startNode The start node
* @return An iterator which when iterated traverses the tree using depth-first, preordered traversal,
* starting at the given start node
*/
protected Iterable lazyTraverseDescendants(final CharSequence startKey, final Node startNode) {
return new Iterable() {
@Override
public Iterator iterator() {
return new LazyIterator() {
Deque stack = new LinkedList();
{
stack.push(new NodeKeyPair(startNode, startKey));
}
@Override
protected NodeKeyPair computeNext() {
if (stack.isEmpty()) {
return endOfData();
}
NodeKeyPair current = stack.pop();
List childNodes = current.node.getOutgoingEdges();
// -> Iterate child nodes in reverse order and so push them onto the stack in reverse order,
// to counteract that pushing them onto the stack alone would otherwise reverse their processing order.
// This ensures that we actually process nodes in ascending alphabetical order.
for (int i = childNodes.size(); i > 0; i--) {
Node child = childNodes.get(i - 1);
stack.push(new NodeKeyPair(child, CharSequences.concatenate(current.key, child.getIncomingEdge())));
}
return current;
}
};
}
};
}
/**
* Encapsulates a node and its associated key. Used internally by {@link #lazyTraverseDescendants}.
*/
protected static class NodeKeyPair {
public final Node node;
public final CharSequence key;
public NodeKeyPair(Node node, CharSequence key) {
this.node = node;
this.key = key;
}
}
/**
* 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 {@link #getKeysStartingWith(CharSequence)} or the
* {@link #getKeyValuePairsForKeysStartingWith(CharSequence)} methods.
*
* This hook is expected to be used by {@link com.googlecode.concurrenttrees.radixreversed.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.
*
* @param rawKey The raw key as stored in the tree
* @return A transformed version of the key
*/
protected CharSequence transformKeyForResult(CharSequence rawKey) {
return rawKey;
}
// ------------- Helper method for searching the tree and associated SearchResult object -------------
/**
* Traverses the tree and finds the node which matches the longest prefix of the given key.
*
* The node returned might be an exact match for the key, in which case {@link SearchResult#charsMatched}
* will equal the length of the key.
*
* The node returned might be an inexact match for the key, in which case {@link SearchResult#charsMatched}
* will be less than the length of the key.
*
* There are two types of inexact match:
*
* -
* An inexact match which ends evenly at the boundary between a node and its children (the rest of the key
* not matching any children at all). In this case if we we wanted to add nodes to the tree to represent the
* rest of the key, we could simply add child nodes to the node found.
*
* -
* An inexact match which ends in the middle of a the characters for an edge stored in a node (the key
* matching only the first few characters of the edge). In this case if we we wanted to add nodes to the
* tree to represent the rest of the key, we would have to split the node (let's call this node found: NF):
*
* -
* Create a new node (N1) which will be the split node, containing the matched characters from the
* start of the edge in NF
*
* -
* Create a new node (N2) which will contain the unmatched characters from the rest of the edge
* in NF, and copy the original edges from NF unmodified into N2
*
* -
* Create a new node (N3) which will be the new branch, containing the unmatched characters from
* the rest of the key
*
* -
* Add N2 as a child of N1
*
* -
* Add N3 as a child of N1
*
* -
* In the parent node of NF, replace the edge pointing to NF with an edge pointing instead
* to N1. If we do this step atomically, reading threads are guaranteed to never see "invalid"
* data, only either the old data or the new data
*
*
*
*
* The {@link SearchResult#classification} is an enum value based on its classification of the
* match according to the descriptions above.
*
* @param key a key for which the node matching the longest prefix of the key is required
* @return A {@link SearchResult} object which contains the node matching the longest prefix of the key, its
* parent node, the number of characters of the key which were matched in total and within the edge of the
* matched node, and a {@link SearchResult#classification} of the match as described above
*/
SearchResult searchTree(CharSequence key) {
Node parentNodesParent = null;
Node parentNode = null;
Node currentNode = root;
int charsMatched = 0, charsMatchedInNodeFound = 0;
final int keyLength = key.length();
outer_loop: while (charsMatched < keyLength) {
Node nextNode = currentNode.getOutgoingEdge(key.charAt(charsMatched));
if (nextNode == null) {
// Next node is a dead end...
//noinspection UnnecessaryLabelOnBreakStatement
break outer_loop;
}
parentNodesParent = parentNode;
parentNode = currentNode;
currentNode = nextNode;
charsMatchedInNodeFound = 0;
CharSequence currentNodeEdgeCharacters = currentNode.getIncomingEdge();
for (int i = 0, numEdgeChars = currentNodeEdgeCharacters.length(); i < numEdgeChars && charsMatched < keyLength; i++) {
if (currentNodeEdgeCharacters.charAt(i) != key.charAt(charsMatched)) {
// Found a difference in chars between character in key and a character in current node.
// Current node is the deepest match (inexact match)....
break outer_loop;
}
charsMatched++;
charsMatchedInNodeFound++;
}
}
return new SearchResult(key, currentNode, charsMatched, charsMatchedInNodeFound, parentNode, parentNodesParent);
}
/**
* Encapsulates results of searching the tree for a node for which a given key is a prefix. Encapsulates the node
* found, its parent node, its parent's parent node, and the number of characters matched in the current node and
* in total.
*
* Also classifies the search result so that algorithms in methods which use this SearchResult, when adding nodes
* and removing nodes from the tree, can select appropriate strategies based on the classification.
*/
static class SearchResult {
final CharSequence key;
final Node nodeFound;
final int charsMatched;
final int charsMatchedInNodeFound;
final Node parentNode;
final Node parentNodesParent;
final Classification classification;
enum Classification {
EXACT_MATCH,
INCOMPLETE_MATCH_TO_END_OF_EDGE,
INCOMPLETE_MATCH_TO_MIDDLE_OF_EDGE,
KEY_ENDS_MID_EDGE,
INVALID // INVALID is never used, except in unit testing
}
SearchResult(CharSequence key, Node nodeFound, int charsMatched, int charsMatchedInNodeFound, Node parentNode, Node parentNodesParent) {
this.key = key;
this.nodeFound = nodeFound;
this.charsMatched = charsMatched;
this.charsMatchedInNodeFound = charsMatchedInNodeFound;
this.parentNode = parentNode;
this.parentNodesParent = parentNodesParent;
// Classify this search result...
this.classification = classify(key, nodeFound, charsMatched, charsMatchedInNodeFound);
}
protected Classification classify(CharSequence key, Node nodeFound, int charsMatched, int charsMatchedInNodeFound) {
if (charsMatched == key.length()) {
if (charsMatchedInNodeFound == nodeFound.getIncomingEdge().length()) {
return Classification.EXACT_MATCH;
}
else if (charsMatchedInNodeFound < nodeFound.getIncomingEdge().length()) {
return Classification.KEY_ENDS_MID_EDGE;
}
}
else if (charsMatched < key.length()) {
if (charsMatchedInNodeFound == nodeFound.getIncomingEdge().length()) {
return Classification.INCOMPLETE_MATCH_TO_END_OF_EDGE;
}
else if (charsMatchedInNodeFound < nodeFound.getIncomingEdge().length()) {
return Classification.INCOMPLETE_MATCH_TO_MIDDLE_OF_EDGE;
}
}
throw new IllegalStateException("Unexpected failure to classify SearchResult: " + this);
}
@Override
public String toString() {
return "SearchResult{" +
"key=" + key +
", nodeFound=" + nodeFound +
", charsMatched=" + charsMatched +
", charsMatchedInNodeFound=" + charsMatchedInNodeFound +
", parentNode=" + parentNode +
", parentNodesParent=" + parentNodesParent +
", classification=" + classification +
'}';
}
}
// ------------- Helper method for pretty-printing tree (not public API) -------------
@Override
public Node getNode() {
return root;
}
}