source: java/ecj/cecj/problems/TestBasedProblemCachingDecorator.java @ 90

package cecj.problems;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import cecj.interaction.InteractionResult;
import cecj.utils.Pair;

import ec.EvolutionState;
import ec.Individual;
import ec.util.Parameter;

public class TestBasedProblemCachingDecorator extends TestBasedProblem {
        public static final String P_CACHE_SIZE = "cache-size";
        public static final String P_INNER_PROBLEM = "inner-problem";

        public static final int UNBOUNDED_CACHE = Integer.MAX_VALUE;

        private Map<Pair<Individual>, Pair<? extends InteractionResult>> cache;
        private Map<Pair<Individual>, Integer> LRUtimer;

        private TestBasedProblem problem;
        private int cacheSizeLimit;

        @Override
        public void setup(EvolutionState state, Parameter base) {
                super.setup(state, base);
                
                Parameter innerProblemParam = base.push(P_INNER_PROBLEM);
                problem = (TestBasedProblem) state.parameters
                        .getInstanceForParameter(innerProblemParam, null, TestBasedProblem.class);
                problem.setup(state, base);

                Parameter cacheSizeParam = base.push(P_CACHE_SIZE);
                cacheSizeLimit = state.parameters.getIntWithDefault(cacheSizeParam, null, UNBOUNDED_CACHE);

                cache = new HashMap<Pair<Individual>, Pair<? extends InteractionResult>>();
                LRUtimer = new HashMap<Pair<Individual>, Integer>();
        }

        public TestBasedProblem getProblem() {
                return problem;
        }
        
        @Override
        public Pair<? extends InteractionResult> test(EvolutionState state, Individual candidate,
                        Individual test) {

                Pair<Individual> key = new Pair<Individual>(candidate, test);
                Pair<? extends InteractionResult> result = cache.get(key);
                if (result == null) {
                        result = problem.test(state, candidate, test);
                        cache.put(key, result);
                }

                LRUtimer.put(key, state.generation);
                if (cache.size() > cacheSizeLimit) {
                        clearLeastRecentlyUsed();
                }

                return result;
        }

        /**
         * Clears least recently used pairs of individuals. Sorts the list of stored pairs of
         * individuals according to time of last use. Removes a half of cache storage.
         */
        private void clearLeastRecentlyUsed() {
                List<Pair<Individual>> list = new ArrayList<Pair<Individual>>(LRUtimer.keySet());
                Collections.sort(list, new Comparator<Pair<Individual>>() {
                        public int compare(Pair<Individual> o1, Pair<Individual> o2) {
                                if (LRUtimer.get(o1) > LRUtimer.get(o2)) {
                                        return -1;
                                } else if (LRUtimer.get(o1) < LRUtimer.get(o2)) {
                                        return 1;
                                } else {
                                        return 0;
                                }
                        }
                });

                for (int i = cacheSizeLimit / 2; i < list.size(); i++) {
                        cache.remove(list.get(i));
                        LRUtimer.remove(list.get(i));
                }
        }
}