#163 Multithreaded breeder

[Jonah Caplan]

I found this useful... program parallelism by evaluating multiple chromosomes at once:

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

import org.jgap.BulkFitnessFunction;
import org.jgap.Configuration;
import org.jgap.IChromosome;
import org.jgap.Population;
import org.jgap.impl.GABreeder;

public class MultiThreadGABreeder extends GABreeder {

    public static int NUM_THREADS = 3;

    @Override
    protected void updateChromosomes(Population a_pop, Configuration a_conf) {
        int currentPopSize = a_pop.size();
        // Ensure all chromosomes are updated.
        // -----------------------------------
        BulkFitnessFunction bulkFunction = a_conf.getBulkFitnessFunction();
        boolean bulkFitFunc = (bulkFunction != null);
        if (!bulkFitFunc) {
            ExecutorService executor = Executors
                    .newFixedThreadPool(NUM_THREADS);
            for (int i = 0; i < currentPopSize; i++) {
                final IChromosome chrom = a_pop.getChromosome(i);
                executor.execute(new Runnable() {
                    public void run() {
                        chrom.getFitnessValue();
                    }
                });
            }
            executor.shutdown();
            while(!executor.isTerminated());
        }
    }

}