[galib] Threaded Evaluator

[Glenn Sugden]

Here's ex1.C with my threaded modifications (note that you should probably be: using a queue for
some maximum number of threads (e.g., number of available cores - 1) instead of threading the
entire population, as well as more thorough error checking - but that's an exercise left to the 
reader :-)


/* ----------------------------------------------------------------------------
 ex1.C
 mbwall 28jul94
 Copyright (c) 1995-1996  Massachusetts Institute of Technology
 
 DESCRIPTION:
 Example program for the SimpleGA class and 2DBinaryStringGenome class.
 This program tries to fill the 2Dgenome with alternating 1s and 0s.
 This example uses the default crossover (single point), default mutator
 (uniform random bit flip), and default initializer (uniform random) for the
 2D genome.
 Notice that one-point crossover is not necessarily the best kind of crossover
 to use if you want to generate a 'good' genome with this kind of objective
 function.  But it does work.
 ---------------------------------------------------------------------------- */
//vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
//| Modifications for a threaded evaluator by Glenn Sugden, 2011-09-03 |
//^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

#include <ga/GASimpleGA.h>	// we're going to use the simple GA
#include <ga/GA2DBinStrGenome.h> // and the 2D binary string genome
#include <ga/std_stream.h>

#define cout STD_COUT

//vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv

#include <assert.h>
#include <pthread.h>

extern void MyEvaluator( GAPopulation & p );
static void *thread_function( void *parameters );

//^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

float Objective( GAGenome & ); // This is the declaration of our obj function.
                               // The definition comes later in the file.

int main( int argc, char **argv )
{
    cout << "Example 1\n\n";
    cout << "This program tries to fill a 2DBinaryStringGenome with\n";
    cout << "alternating 1s and 0s using a SimpleGA\n\n";
    cout.flush();
    
        // See if we've been given a seed to use (for testing purposes).  When you
        // specify a random seed, the evolution will be exactly the same each time
        // you use that seed number.
    
    for ( int ii = 1; ii < argc; ii++ )
    {
        if ( strcmp( argv[ii++], "seed" ) == 0 )
        {
            GARandomSeed( (unsigned int) atoi( argv[ii] ) );
        }
    }
    
        // Declare variables for the GA parameters and set them to some default values.
    
    int width = 10;
    int height = 5;
    int popsize = 30;
    int ngen = 400;
    float pmut = 0.001;
    float pcross = 0.9;
    
        // Now create the GA and run it.  First we create a genome of the type that
        // we want to use in the GA.  The ga doesn't operate on this genome in the
        // optimization - it just uses it to clone a population of genomes.
    
    GA2DBinaryStringGenome genome( width, height, Objective );
    
        // Now that we have the genome, we create the genetic algorithm and set
        // its parameters - number of generations, mutation probability, and crossover
        // probability.  And finally we tell it to evolve itself.
    
    GASimpleGA ga( genome );
    ga.populationSize( popsize );
    ga.nGenerations( ngen );
    ga.pMutation( pmut );
    ga.pCrossover( pcross );
    
//vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
    
    GAPopulation *pop = const_cast< GAPopulation * >( &ga.population());
    
    assert(pop);
    
    GAPopulation    *newpop = pop->clone();
    
    assert(newpop);
    
    newpop->userData( ga.userData() );
    
    newpop->evaluator( MyEvaluator );
    
    ga.population( *newpop );
    
//^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    
    ga.evolve();
    
        // Now we print out the best genome that the GA found.
    
    cout << "The GA found:\n" << ga.statistics().bestIndividual() << "\n";
        
    // That's it!
    
    return 0;
}

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extern void MyEvaluator( GAPopulation & p )
{
    pthread_attr_t thread_attr;
    
    pthread_t *threads = new pthread_t[p.size()];
    
    assert( threads );
    
    int rc = pthread_attr_init( &thread_attr );
    
    if ( rc )
        std::cerr << "Error #" << rc << " in pthread_attr_init." << std::endl;
    
    rc = pthread_attr_setdetachstate( &thread_attr, PTHREAD_CREATE_JOINABLE );
    
    if ( rc )
        std::cerr << "Error #" << rc << " in pthread_attr_setdetachstate." << std::endl;
        
    for ( int i = 0; i < p.size(); i++ )
    {
        void* parameters = &p.individual( i );
        
        rc = pthread_create( &threads[i], &thread_attr, thread_function, parameters );
        
        if ( rc )
            std::cerr << "Error #" << rc << " for individual: " << i << " in pthread_create." << std::endl;
    }
    
    for ( int i = 0; i < p.size(); i++ )
    {
        void* value_ptr;
        
        rc = pthread_join(threads[i], &value_ptr);

        if ( rc )
            std::cerr << "Error #" << rc << " for individual: " << i << " in pthread_join." << std::endl;

        assert(value_ptr == &p.individual( i )); // Sanity check...
    }
    
    delete[] threads;
}

static void *thread_function( void *parameters )
{
    GAGenome* genome = (GAGenome*) parameters;
    
    genome->evaluate();
    
    pthread_exit( parameters );
    
    return (0); // To get rid of compiler warning.
}

//^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

    // This is the objective function.  All it does is check for alternating 0s and
    // 1s.  If the gene is odd and contains a 1, the fitness is incremented by 1.
    // If the gene is even and contains a 0, the fitness is incremented by 1.  No
    // penalties are assigned.
    //   We have to do the cast because a plain, generic GAGenome doesn't have
    // the members that a GA2DBinaryStringGenome has.  And it's ok to cast it
    // because we know that we will only get GA2DBinaryStringGenomes and
    // nothing else.

float Objective( GAGenome& g )
{
    GA2DBinaryStringGenome & genome = (GA2DBinaryStringGenome &) g;
    float score = 0.0;
    int count = 0;
    for ( int i = 0; i < genome.width(); i++ )
    {
        for ( int j = 0; j < genome.height(); j++ )
        {
            if ( genome.gene( i, j ) == 0 && count % 2 == 0 )
                score += 1.0;
            if ( genome.gene( i, j ) == 1 && count % 2 != 0 )
                score += 1.0;
            count++;
        }
    }

    return score;
}