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Concurrent Radix Trees and Concurrent Suffix Trees for Java.
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/**
* 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.suffix;
import com.googlecode.concurrenttrees.common.CharSequences;
import com.googlecode.concurrenttrees.common.KeyValuePair;
import com.googlecode.concurrenttrees.common.LazyIterator;
import com.googlecode.concurrenttrees.radix.ConcurrentRadixTree;
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.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
/**
* An implementation of {@link SuffixTree} 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.
*
* This implementation is based on {@link ConcurrentRadixTree}.
*
* @author Niall Gallagher
*/
public class ConcurrentSuffixTree implements SuffixTree, PrettyPrintable, Serializable {
class ConcurrentSuffixTreeImpl extends ConcurrentRadixTree {
public ConcurrentSuffixTreeImpl(NodeFactory nodeFactory) {
super(nodeFactory);
}
@Override
protected void acquireWriteLock() {
super.acquireWriteLock();
}
@Override
protected void releaseWriteLock() {
super.releaseWriteLock();
}
}
private final ConcurrentSuffixTreeImpl> radixTree;
private final ConcurrentMap valueMap;
/**
* Creates a new {@link ConcurrentSuffixTree} which will use the given {@link NodeFactory} to create nodes.
*
* @param nodeFactory An object which creates {@link com.googlecode.concurrenttrees.radix.node.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 ConcurrentSuffixTree(NodeFactory nodeFactory) {
this.radixTree = new ConcurrentSuffixTreeImpl>(nodeFactory);
this.valueMap = new ConcurrentHashMap();
}
/**
* {@inheritDoc}
*/
@Override
public O put(CharSequence key, O value) {
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");
}
radixTree.acquireWriteLock();
try {
// We convert to string (for now) due to lack of equals() and hashCode() support in CharSequence...
String keyString = CharSequences.toString(key);
// Put/replace value in map before we add suffixes to the tree
// (prevents reading threads finding suffixes with no value)...
final O replacedValue = valueMap.put(keyString, value);
// We only need to modify the tree if we have not added this key before...
if (replacedValue == null) {
addSuffixesToRadixTree(keyString);
}
return replacedValue; // might be null
}
finally {
radixTree.releaseWriteLock();
}
}
/**
* {@inheritDoc}
*/
@Override
public O putIfAbsent(CharSequence key, O value) {
radixTree.acquireWriteLock();
try {
// We convert to string (for now) due to lack of equals() and hashCode() support in CharSequence...
String keyString = CharSequences.toString(key);
// Put/replace value in map only if key is absent, before we add suffixes to the tree
// (prevents reading threads finding suffixes with no value)...
final O existingValue = valueMap.putIfAbsent(keyString, value);
// We only need to modify the tree if we have not added this key before...
if (existingValue == null) {
// Key is not already in tree, add it now...
addSuffixesToRadixTree(keyString);
}
// else we have not made any changes
return existingValue; // might be null
}
finally {
radixTree.releaseWriteLock();
}
}
/**
* {@inheritDoc}
*/
@Override
public boolean remove(CharSequence key) {
radixTree.acquireWriteLock();
try {
// We convert to string (for now) due to lack of equals() and hashCode() support in CharSequence...
String keyString = CharSequences.toString(key);
O value = valueMap.get(keyString);
if (value == null) {
// Key was not stored, no need to do anything, return false...
return false;
}
// Remove suffixes from the tree...
removeSuffixesFromRadixTree(keyString);
valueMap.remove(keyString);
return true;
}
finally {
radixTree.releaseWriteLock();
}
}
void addSuffixesToRadixTree(String keyAsString) {
Iterable suffixes = CharSequences.generateSuffixes(keyAsString);
for (CharSequence suffix : suffixes) {
Set originalKeyRefs = radixTree.getValueForExactKey(suffix);
if (originalKeyRefs == null) {
originalKeyRefs = createSetForOriginalKeys();
radixTree.put(suffix, originalKeyRefs);
}
originalKeyRefs.add(keyAsString);
}
}
void removeSuffixesFromRadixTree(String keyAsString) {
Iterable suffixes = CharSequences.generateSuffixes(keyAsString);
for (CharSequence suffix : suffixes) {
Set originalKeyRefs = radixTree.getValueForExactKey(suffix);
originalKeyRefs.remove(keyAsString);
if (originalKeyRefs.isEmpty()) {
// We just removed the last original key which shares this suffix.
// Remove the suffix from the tree entirely...
radixTree.remove(suffix);
}
// else leave the suffix in the tree, as it is a common suffix of another key.
}
}
/**
* Creates a new {@link Set} in which original keys from which a suffix was generated can be stored.
*
* By default this method creates a new concurrent set based on {@link ConcurrentHashMap}.
*
* Subclasses could override this method to create an alternative set.
*
* Specifically it is expected that this would be useful in unit tests,
* where sets with consistent iteration order would be useful.
*
* @return A new {@link Set} in which original keys from which a suffix was generated can be stored
*/
protected Set createSetForOriginalKeys() {
return Collections.newSetFromMap(new ConcurrentHashMap());
}
/**
* {@inheritDoc}
*/
@Override
public O getValueForExactKey(CharSequence key) {
// We convert to string (for now) due to lack of equals() and hashCode() support in CharSequence...
String keyString = CharSequences.toString(key);
return valueMap.get(keyString);
}
/**
* {@inheritDoc}
*/
@Override
public Iterable getKeysEndingWith(CharSequence suffix) {
Set originalKeys = radixTree.getValueForExactKey(suffix);
if (originalKeys == null) {
return Collections.emptySet();
}
// Cast to Set, as we have internally implemented tree with strings...
@SuppressWarnings({"unchecked", "UnnecessaryLocalVariable"})
Set results = (Set) originalKeys;
return results;
}
/**
* {@inheritDoc}
*/
@Override
public Iterable getValuesForKeysEndingWith(final CharSequence suffix) {
return new Iterable() {
@Override
public Iterator iterator() {
return new LazyIterator() {
Iterator originalKeys = nullSafeIterator(radixTree.getValueForExactKey(suffix));
@Override
protected O computeNext() {
O value = null;
while (value == null) {
if (!originalKeys.hasNext()) {
return endOfData();
}
String originalKey = originalKeys.next();
value = valueMap.get(originalKey);
}
return value;
}
};
}
};
}
/**
* {@inheritDoc}
*/
@Override
public Iterable> getKeyValuePairsForKeysEndingWith(final CharSequence suffix) {
return new Iterable>() {
@Override
public Iterator> iterator() {
return new LazyIterator>() {
Iterator originalKeys = nullSafeIterator(radixTree.getValueForExactKey(suffix));
@Override
protected KeyValuePair computeNext() {
String originalKey = null;
O value = null;
while (value == null) {
if (!originalKeys.hasNext()) {
return endOfData();
}
originalKey = originalKeys.next();
value = valueMap.get(originalKey);
}
return new ConcurrentRadixTree.KeyValuePairImpl(originalKey, value);
}
};
}
};
}
/**
* {@inheritDoc}
*/
@Override
public Iterable getKeysContaining(final CharSequence fragment) {
return new Iterable() {
@Override
public Iterator iterator() {
return new LazyIterator() {
Iterator> originalKeysSets = radixTree.getValuesForKeysStartingWith(fragment).iterator();
Iterator keyIterator = Collections.emptyList().iterator();
// A given fragment can be contained many times within the same key, so track keys processed
// so far, so that we can avoid re-processing the same key multiple times...
Set keysAlreadyProcessed = new HashSet();
@Override
protected CharSequence computeNext() {
String nextKey = null;
while (nextKey == null) {
while (!keyIterator.hasNext()) {
if (!originalKeysSets.hasNext()) {
return endOfData();
}
keyIterator = originalKeysSets.next().iterator();
}
nextKey = keyIterator.next();
if (!keysAlreadyProcessed.add(nextKey)) {
// The set already contained the key, hence we don't reprocess it...
nextKey = null;
}
}
return nextKey;
}
};
}
};
}
/**
* {@inheritDoc}
*/
@Override
public Iterable getValuesForKeysContaining(final CharSequence fragment) {
return new Iterable() {
@Override
public Iterator iterator() {
return new LazyIterator() {
Iterator> originalKeysSets = radixTree.getValuesForKeysStartingWith(fragment).iterator();
Iterator keyIterator = Collections.emptyList().iterator();
// A given fragment can be contained many times within the same key, so track keys processed
// so far, so that we can avoid re-processing the same key multiple times...
Set keysAlreadyProcessed = new HashSet();
@Override
protected O computeNext() {
O value = null;
while (value == null) {
while (!keyIterator.hasNext()) {
if (!originalKeysSets.hasNext()) {
return endOfData();
}
keyIterator = originalKeysSets.next().iterator();
}
String originalKey = keyIterator.next();
if (keysAlreadyProcessed.add(originalKey)) {
// Key was not in the already-processed set, so proceed with looking up the value...
value = valueMap.get(originalKey);
// value could still be null due to race condition if key/value was removed while
// iterating, hence if so, we loop again to find the next non-null key/value...
}
}
return value;
}
};
}
};
}
/**
* {@inheritDoc}
*/
@Override
public Iterable> getKeyValuePairsForKeysContaining(final CharSequence fragment) {
return new Iterable>() {
@Override
public Iterator> iterator() {
return new LazyIterator>() {
Iterator> originalKeysSets = radixTree.getValuesForKeysStartingWith(fragment).iterator();
Iterator keyIterator = Collections.emptyList().iterator();
// A given fragment can be contained many times within the same key, so track keys processed
// so far, so that we can avoid re-processing the same key multiple times...
Set keysAlreadyProcessed = new HashSet();
@Override
protected KeyValuePair computeNext() {
String originalKey = null;
O value = null;
while (value == null) {
while (!keyIterator.hasNext()) {
if (!originalKeysSets.hasNext()) {
return endOfData();
}
keyIterator = originalKeysSets.next().iterator();
}
originalKey = keyIterator.next();
if (keysAlreadyProcessed.add(originalKey)) {
// Key was not in the already-processed set, so proceed with looking up the value...
value = valueMap.get(originalKey);
// value could still be null due to race condition if key/value was removed while
// iterating, hence if so, we loop again to find the next non-null key/value...
}
}
return new ConcurrentRadixTree.KeyValuePairImpl(originalKey, value);
}
};
}
};
}
/**
* {@inheritDoc}
*/
@Override
public int size() {
return valueMap.size();
}
/**
* Utility method to return an iterator for the given iterable, or an empty iterator if the iterable is null.
*/
@SuppressWarnings({"JavaDoc"})
static Iterator nullSafeIterator(Iterable iterable) {
return iterable == null ? Collections.emptyList().iterator() : iterable.iterator();
}
@Override
public Node getNode() {
return radixTree.getNode();
}
}