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/*
* Copyright 2009 David Jurgens
*
* This file is part of the S-Space package and is covered under the terms and
* conditions therein.
*
* The S-Space package is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as published
* by the Free Software Foundation and distributed hereunder to you.
*
* THIS SOFTWARE IS PROVIDED "AS IS" AND NO REPRESENTATIONS OR WARRANTIES,
* EXPRESS OR IMPLIED ARE MADE. BY WAY OF EXAMPLE, BUT NOT LIMITATION, WE MAKE
* NO REPRESENTATIONS OR WARRANTIES OF MERCHANT- ABILITY OR FITNESS FOR ANY
* PARTICULAR PURPOSE OR THAT THE USE OF THE LICENSED SOFTWARE OR DOCUMENTATION
* WILL NOT INFRINGE ANY THIRD PARTY PATENTS, COPYRIGHTS, TRADEMARKS OR OTHER
* RIGHTS.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see
*
* All instances of this class are thread-safe.
*
* @author David Jurgens
*/
public class WordComparator {
/**
* The queue from which worker threads run word-word comparisons
*/
private final BlockingQueue workQueue;
/**
* Creates this {@code WordComparator} with as many threads as processors.
*/
public WordComparator() {
this(Runtime.getRuntime().availableProcessors());
}
/**
* Creates this {@code WordComparator} with the specified number of threads.
*/
public WordComparator(int numThreads) {
workQueue = new LinkedBlockingQueue();
for (int i = 0; i < numThreads; ++i) {
new WorkerThread(workQueue, 10).start();
}
}
/**
* Compares the provided word to all other words in the provided {@link
* SemanticSpace} and return the specified number of words that were most
* similar according to the specified similarity measure.
*
* @return the most similar words, or {@code null} if the provided word was
* not in the semantic space.
*/
public SortedMultiMap getMostSimilar(
final String word, final SemanticSpace sspace,
int numberOfSimilarWords, Similarity.SimType similarityType) {
Vector v = sspace.getVector(word);
// if the semantic space did not have the word, then return null
if (v == null) {
return null;
}
final Vector vector = v;
Set words = sspace.getWords();
// the most-similar set will automatically retain only a fixed number
// of elements
final SortedMultiMap mostSimilar =
new BoundedSortedMultiMap(numberOfSimilarWords,
false);
// The semaphore used to block until all the words have been compared.
// Use word-2 since we don't process the comparison of the word to
// itself, and we want one permit to be availabe after the last word is
// compared. The negative ensures that the release() must happen before
// the main thread's acquire() will return.
final Semaphore comparisons = new Semaphore(0 - (words.size() - 2));
// loop through all the other words computing their
// similarity
int submitted = 0;
for (String s : words) {
final String other = s;
// skip if it is ourselves
if (word.equals(other))
continue;
workQueue.offer(new Comparison(
comparisons, sspace, vector,
other, similarityType, mostSimilar));
}
try {
comparisons.acquire();
} catch (InterruptedException ie) {
// check whether we were interrupted while still waiting for the
// comparisons to finish
if (comparisons.availablePermits() < 1) {
throw new IllegalStateException(
"interrupted while waiting for word comparisons to finish",
ie);
}
}
//System.out.println(executor.shutdownNow())
return mostSimilar;
}
/**
* A comparison task that compares the vector for the other word and updates
* the mapping from similarity to word.
*/
private static class Comparison implements Runnable {
private final Semaphore semaphore;
SemanticSpace sspace;
Vector vector;
String other;
Similarity.SimType similarityMeasure;
MultiMap mostSimilar;
public Comparison(Semaphore semaphore,
SemanticSpace sspace,
Vector vector,
String other,
Similarity.SimType similarityMeasure,
MultiMap mostSimilar) {
this.semaphore = semaphore;
this.sspace = sspace;
this.vector = vector;
this.other = other;
this.similarityMeasure = similarityMeasure;
this.mostSimilar = mostSimilar;
}
public void run() {
try {
Vector otherV = sspace.getVector(other);
Double similarity = Similarity.getSimilarity(
similarityMeasure, vector, otherV);
// lock on the Map, as it is not thread-safe
synchronized(mostSimilar) {
mostSimilar.put(similarity, other);
}
} catch (Exception e) {
// Rethrow any reflection-related exception, as this situation
// should not normally occur since the Method being invoked
// comes directly from the Similarity class.
throw new Error(e);
} finally {
// notify that the word has been processed regardless of whether
// an error occurred
semaphore.release();
}
}
}
}