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MYRA is a collection of Ant Colony Optimization (ACO) algorithms for the data mining classification task.
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/*
 * ParallelScheduler.java
 * (this file is part of MYRA)
 * 
 * Copyright 2008-2015 Fernando Esteban Barril Otero
 * 
 * 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 myra;

import static myra.Config.CONFIG;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadFactory;

import myra.Archive.SynchronizedArchive;

/**
 * Parallel implementation of a Scheduler. Activites executed by
 * this scheduler need to be thread-safe.
 * 
 * @author Fernando Esteban Barril Otero
 */
public class ParallelScheduler> extends Scheduler {
    /**
     * Tasks executor service.
     */
    private ExecutorService executor;

    /**
     * Creates a new ParallelScheduler.
     */
    public ParallelScheduler() {
        this(null, CONFIG.get(COLONY_SIZE));
    }

    /**
     * Creates a new ParallelScheduler.
     * 
     * @param capacity
     *            number of candidate solutions stored at each iteration.
     */
    public ParallelScheduler(int capacity) {
        this(null, capacity);
    }

    /**
     * Creates a new ParallelScheduler.
     * 
     * @param activity
     *            the (wrapped) activity.
     */
    public ParallelScheduler(Activity activity) {
        this(activity, CONFIG.get(COLONY_SIZE));
    }

    /**
     * Creates a new ParallelScheduler.
     * 
     * @param activity
     *            the (wrapped) activity.
     * @param capacity
     *            number of candidate solutions stored at each iteration.
     */
    public ParallelScheduler(Activity activity, int capacity) {
        super(activity, capacity);
    }

    @Override
    protected void initialise() {
        super.initialise();
        // initialises the thread pool
        executor = Executors.newFixedThreadPool(CONFIG.get(PARALLEL),
                                                new ThreadFactory() {
                                                    private int id = 0;

                                                    public Thread newThread(Runnable r) {
                                                        return new Thread(r,
                                                                          "ParallelScheduler::worker"
                                                                                  + (id++));
                                                    }
                                                });
    }

    @Override
    protected void create() {
        final CountDownLatch latch =
                new CountDownLatch(CONFIG.get(COLONY_SIZE));
        final Archive pool = new SynchronizedArchive<>(archive);

        for (int i = 0; i < CONFIG.get(COLONY_SIZE); i++) {
            executor.execute(new Runnable() {
                @Override
                public void run() {
                    pool.add(activity.create());
                    latch.countDown();
                }
            });
        }

        try {
            // waits for the creation of trails
            latch.await();
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
    }

    @Override
    public void run() {
        super.run();
        // finilizes the executor threads
        executor.shutdown();
    }
}