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The S-Space Package is a collection of algorithms for building Semantic Spaces as well as a highly-scalable library for designing new distributional semantics algorithms. Distributional algorithms process text corpora and represent the semantic for words as high dimensional feature vectors. This package also includes matrices, vectors, and numerous clustering algorithms. These approaches are known by many names, such as word spaces, semantic spaces, or distributed semantics and rest upon the Distributional Hypothesis: words that appear in similar contexts have similar meanings.

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/*
 * Copyright 2009 Keith Stevens 
 *
 * 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 .
 */

package edu.ucla.sspace.vector;

import java.io.Serializable;

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantReadWriteLock;


/**
 * A decorator of a {@code Vector} which provides atomic concurrent access to
 * another {@code Vector}.  This allows all reads to be done concurrently, while
 * limiting to writing to only one thread at a time.  This does not provide a
 * specific implementation of a {@code Vector}, allowing any {@code Vector}
 * implementation to be made atomic.
 *
 * @author David Jurgens
 * @author Keith Stevens
 */
public class AtomicSparseVector implements SparseDoubleVector, Serializable {

    private static final long serialVersionUID = 1L;

    /**
     * The original {@code SparseDoubleVector} that this {@code AtomicSparseVector}
     * decorates.
     */
    private final SparseDoubleVector vector;

    /**
     * Read lock for non-mutating access to the backing {@code vector}.
     */
    private final Lock readLock;

    /**
     * Write lock for mutating access to the backing {@code vector}.
     */
    private final Lock writeLock;

    /**
     * Creates a new {@code AtomicSparseVector} decorating an already existing
     * {@code Vector}.
     *
     * @param v The vector to decorate.
     */
    public AtomicSparseVector(SparseDoubleVector v) {
        vector = v;

        ReentrantReadWriteLock rwLock = new ReentrantReadWriteLock();
        readLock = rwLock.readLock();
        writeLock = rwLock.writeLock();
    }
    
    /**
     * {@inheritDoc}
     */
    public double addAndGet(int index, double delta) {
        return add(index, delta);
    }

    /**
     * {@inheritDoc}
     */
    public double getAndAdd(int index, double delta) {
        writeLock.lock();
        double value = vector.get(index);
        vector.set(index, value + delta);
        writeLock.unlock();
        return value;
    }

    /**
     * {@inheritDoc}
     */
    public double add(int index, double delta) {
        writeLock.lock();
        double value = vector.add(index, delta);
        writeLock.unlock();
        return value;
    }

    /**
     * {@inheritDoc}
     */
    public double get(int index) {
        readLock.lock();
        double value = vector.get(index);
        readLock.unlock();
        return value;
    }

    /**
     * {@inheritDoc}
     */
    public int[] getNonZeroIndices() {
        return vector.getNonZeroIndices();
    }

    /**
     * {@inheritDoc}
     */
    public Double getValue(int index) {
        return get(index);
    }

    /**
     * Returns the {@link SparseDoubleVector} that backs this instance.
     */
    public SparseDoubleVector getVector() {
        return vector;
    }

    /**
     * {@inheritDoc}
     */
    public double magnitude() {
        readLock.lock();
        double m = vector.magnitude();
        readLock.unlock();
        return m;
    }

    /**
     * {@inheritDoc}
     */
    public void set(int index, double value) {
        writeLock.lock();
        vector.set(index, value);
        writeLock.unlock();
    }

    /**
     * {@inheritDoc}
     */
    public void set(int index, Number value) {
        set(index, value.doubleValue());
    }

    /**
     * {@inheritDoc}
     */
    public double[] toArray() {
        readLock.lock();
        double[] array = vector.toArray();
        readLock.lock();
        return array;
    }

    /**
     * {@inheritDoc}
     */
    public int length() {
        readLock.lock();
        int length = vector.length();
        readLock.unlock();
        return length;
    }
}