source: src/main/java/geniusweb/partiesserver/repository/RunningPartiesRepo.java@ 18

package geniusweb.partiesserver.repository;

import java.util.Collection;
import java.util.Collections;
import java.util.Date;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.logging.Level;

import geniusweb.actions.PartyId;
import tudelft.utilities.listener.DefaultListenable;
import tudelft.utilities.logging.ReportToLogger;
import tudelft.utilities.logging.Reporter;
import tudelft.utilities.repository.NoResourcesNowException;
import tudelft.utilities.repository.Repository;

/**
 * RunningPartiesRepo stores all currently running parties. Listeners are
 * notified when a party is added or removed.
 */
public class RunningPartiesRepo extends DefaultListenable<PartyId>
                implements Repository<PartyId, RunningParty> {
        /**
         * List of currently running parties.
         */
        public static final int MAX_SLOTS = 4;
        private static final RunningPartiesRepo instance = new RunningPartiesRepo(
                        new ReportToLogger("partiesserver"));
        private static final long MAXWAIT_MS = 600000; // 10 minutes
        private final Reporter log;

        // not static to facilitate testing.
        private final Map<PartyId, RunningParty> runningParties = new ConcurrentHashMap<>();

        /**
         * singleton pattern. Do not call this but use {@link #instance()}. Testers
         * can still use this (instead of {@link #instance()) to get a fresn empty
         * runningParties map. We need singleton pattern because tomcat acts as a
         * black box calling us from "nowhere" (it works with annotations).
         */
        RunningPartiesRepo(Reporter reporter) {
                this.log = reporter;
        }

        public static RunningPartiesRepo instance() {
                return instance;
        }

        @Override
        public Collection<RunningParty> list() {
                return Collections.unmodifiableCollection(runningParties.values());
        }

        @Override
        public RunningParty get(PartyId id) {
                return runningParties.get(id);
        }

        @Override
        public void put(RunningParty newParty) throws NoResourcesNowException {
                PartyId id = newParty.getID();
                synchronized (runningParties) {
                        if (runningParties.containsKey(id)) {
                                throw new IllegalArgumentException(
                                                "Party " + newParty + " already in the repository");
                        }
                        if (availableSlots() <= 0) {
                                Date date = estimateCleanupTime();
                                throw new NoResourcesNowException(
                                                "There are currently no free slots to register party "
                                                                + newParty,
                                                date);
                        }
                        runningParties.put(id, newParty);
                }
                notifyListeners(id);
        }

        @Override
        public void replace(RunningParty newParty) {
                PartyId id = newParty.getID();
                synchronized (runningParties) {
                        if (!runningParties.containsKey(id)) {
                                throw new IllegalArgumentException(
                                                "Party " + newParty + " is not in the repository");
                        }
                        runningParties.put(id, newParty);
                }
                notifyListeners(id);

        }

        /**
         * @return an estimate of when the repo will be cleaned up (party gets
         *         terminated). Returns at most {@link #MAXWAIT_MS}. May return time
         *         before NOW if party is was expected to be already terminated.
         */
        public Date estimateCleanupTime() {
                long now = System.currentTimeMillis();
                Date date = new Date(now + MAXWAIT_MS);
                synchronized (runningParties) {
                        for (RunningParty party : runningParties.values()) {
                                if (party.getEndDate().before(date)) {
                                        date = party.getEndDate();
                                }
                        }
                }
                return date;
        }

        @Override
        public void remove(PartyId id) {
                synchronized (runningParties) {
                        RunningParty party = runningParties.get(id);
                        if (party == null) {
                                return; // no such party is there right now.
                        }
                        runningParties.remove(id);
                        try {
                                party.getParty().terminate();
                        } catch (Throwable e) {
                                log.log(Level.WARNING,
                                                "Party " + id + " did not terminate properly", e);

                        }
                }
                notifyListeners(id);
        }

        /**
         * @return the maximum number of slots in this factory. Each slot can run
         *         one party.
         */

        public int maximumSlots() {
                return MAX_SLOTS;
        }

        /**
         * 
         * @return the currently available number of slots in this factory. Each
         *         slot can run one party.
         */

        public int availableSlots() {
                synchronized (runningParties) {
                        return MAX_SLOTS - runningParties.size();
                }
        }

}