PoolInfoMap.java

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package org.dcache.resilience.data;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.collect.HashMultimap;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Multimap;
import com.google.common.collect.Sets;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.Set;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import java.util.regex.Pattern;
import java.util.stream.Collectors;

import diskCacheV111.poolManager.CostModule;
import diskCacheV111.poolManager.PoolSelectionUnit;
import diskCacheV111.poolManager.PoolSelectionUnit.SelectionPool;
import diskCacheV111.poolManager.PoolSelectionUnit.SelectionPoolGroup;
import diskCacheV111.poolManager.PoolSelectionUnit.SelectionUnit;
import diskCacheV111.poolManager.StorageUnit;
import diskCacheV111.pools.PoolCostInfo;
import diskCacheV111.pools.PoolV2Mode;
import diskCacheV111.vehicles.PoolManagerPoolInformation;
import org.dcache.poolmanager.PoolInfo;
import org.dcache.poolmanager.PoolMonitor;
import org.dcache.resilience.handlers.PoolInfoChangeHandler;
import org.dcache.resilience.util.CopyLocationExtractor;
import org.dcache.resilience.util.MapInitializer;
import org.dcache.resilience.util.RandomSelectionStrategy;
import org.dcache.resilience.util.StorageUnitInfoExtractor;
import org.dcache.util.NonReindexableList;
import org.dcache.vehicles.FileAttributes;

/**
 * <p>Serves as the central locus of pool-related information.</p>
 *
 * <p>The internal data structures hold a list of pool names and pool groups
 *      which will always assign a new index number to a new member even if
 *      some of the current members happen to be deleted via a PoolSelectionUnit
 *      operation.</p>
 *
 * <p>The reason for doing this is to be able to store most of the pool info
 *      associated with a given file or pool operation in progress as index
 *      references, allowing the {@link FileOperation} to use 4-byte rather
 *       than 8-byte 'references'.</p>
 *
 * <p>The relational tables represented by multimaps of indices
 *      capture pool and storage unit membership in pool groups.  There are
 *      also three maps which define the resilience constraints for a given
 *      storage unit, the tags for a pool, and the live mode and cost
 *      information for a pool.</p>
 *
 * <p>This class also provides methods for determining the resilient group
 *      of a given pool, the storage groups connected to a given pool group,
 *      whether a pool or pool group is resilient, and whether a pool group can
 *      satisfy the constraints defined by the storage units bound to it.</p>
 *
 * <p>{@link #apply(PoolInfoDiff)}
 *      empties and rebuilds pool-related information based on a diff obtained
 *      from {@link #compare(PoolMonitor)}.  An empty diff is equivalent to
 *      a load operation (at initialization). These methods are called by
 *      the {@link MapInitializer} at startup, and
 *      thereafter by the {@link PoolInfoChangeHandler}</p>
 *
 * <p>This class benefits from read-write synchronization, since there will
 *      be many more reads of what is for the most part stable information
 *      (note that the periodically refreshed information is synchronized
 *      within the PoolInformation object itself; hence changes
 *      to those values do not require a write lock; e.g., #updatePoolStatus.)</p>
 *
 * <p>Class is not marked final for stubbing/mocking purposes.</p>
 */
public class PoolInfoMap {
    private static final Logger LOGGER = LoggerFactory.getLogger(
                    PoolInfoMap.class);

    private static StorageUnitConstraints getConstraints(Integer storageUnit,
                                                         Map<Integer, ResilienceMarker> constraints) {
        ResilienceMarker marker = constraints.get(storageUnit);

        if (marker != null && !(marker instanceof StorageUnitConstraints)) {
            String message = "Index " + storageUnit + " does not correspond "
                            + "to a storage unit";
            throw new NoSuchElementException(message);
        }

        StorageUnitConstraints sconstraints = (StorageUnitConstraints) marker;
        int required;
        Set<String> oneCopyPer;

        if (sconstraints != null) {
            required = sconstraints.getRequired();
            oneCopyPer = sconstraints.getOneCopyPer();
        } else {
            /*
             *  This can occur if a link pointing to the pool group of this pool
             *  has been changed or removed, or a storage unit removed from
             *  the unit group associated with it.  The policy here will
             *  be to consider these files non-existent for the purpose of
             *  replication.  By leaving required = 1 we guarantee that
             *  the entry remains "invisible" to replication handling
             *  and no action will be taken.
             */
            required = 1;
            oneCopyPer = null;
        }

        return new StorageUnitConstraints(required, oneCopyPer);
    }

    private final List<String>                   pools              = new NonReindexableList<>();
    private final List<String>                   groups             = new NonReindexableList<>();
    private final List<String>                   sunits             = new NonReindexableList<>();
    private final Map<Integer, ResilienceMarker> markers            = new HashMap<>();
    private final Map<Integer, ResilienceMarker> constraints        = new HashMap<>();
    private final Map<Integer, PoolInformation>  poolInfo           = new HashMap<>();
    private final Multimap<Integer, Integer>     poolGroupToPool    = HashMultimap.create();
    private final Multimap<Integer, Integer>     poolToPoolGroup    = HashMultimap.create();
    private final Multimap<Integer, Integer>     storageToPoolGroup = HashMultimap.create();
    private final Multimap<Integer, Integer>     poolGroupToStorage = HashMultimap.create();

    private final ReadWriteLock lock  = new ReentrantReadWriteLock(true);
    private final Lock          write = lock.writeLock();
    private final Lock          read  = lock.readLock();

    private boolean useRegex = false;

    /**
     * <p>Called on a dedicated thread.</p>
     *
     * <p>Applies a diff under write lock.</p>
     *
     * <p>Will not clear the NonReindexable lists (pools, groups).
     *      This is to maintain the same indices for the duration of the
     *      life of the JVM, since the other maps may contain live references
     *      to pools or groups.</p>
     */
    public void apply(PoolInfoDiff diff) {
        write.lock();
        try {
            /*
             *  -- Remove stale pools, pool groups and storage units.
             *
             *     Pool removal assumes that the pool has been properly drained
             *     of files first; this is not taken care of here.  Similarly
             *     for the removal of pool groups.
             */
            LOGGER.trace("removing stale pools, pool groups and storage units");
            diff.getOldPools().stream().forEach(this::removePool);
            diff.getOldGroups().stream().forEach(this::removeGroup);
            diff.getOldUnits().stream().forEach(this::removeUnit);

            /*
             *  -- Remove pools from current groups.
             */
            LOGGER.trace("removing pools from pool groups");
            diff.getPoolsRemovedFromPoolGroup().entries()
                .forEach(this::removeFromPoolGroup);

            /*
             *  -- Remove units from current groups.
             */
            LOGGER.trace("removing units from pool groups");
            diff.getUnitsRemovedFromPoolGroup().entries()
                .forEach(this::removeStorageUnit);

            /*
             *  -- Add new storage units, pool groups and pools.
             */
            LOGGER.trace("adding new storage units, pool groups and pools");
            diff.getNewUnits().stream().forEach(this::addStorageUnit);
            diff.getNewGroups().stream().forEach(this::addPoolGroup);
            diff.getNewPools().stream().forEach(pools::add);

            /*
             *  -- Add units to pool groups.
             */
            LOGGER.trace("adding storage units to pool groups");
            diff.getUnitsAddedToPoolGroup().entries().stream()
                .forEach(this::addUnitToPoolGroup);

            /*
             *  -- Add pools to pool groups.
             */
            LOGGER.trace("adding pools to pool groups");
            diff.getPoolsAddedToPoolGroup().entries().stream()
                .forEach(this::addPoolToPoolGroups);

            /*
             *  -- Modify constraints.
             */
            LOGGER.trace("modifying storage unit constraints");
            diff.getConstraints().entrySet().stream()
                .forEach(this::updateConstraints);

            /*
             *  -- Add pool information for the new pools.
             *
             *     The new pools are the only ones to have
             *     entries in the cost info map.
             */
            LOGGER.trace("adding live pool information");
            diff.getPoolCost().keySet().stream()
                              .forEach((p) ->
                                    setPoolInfo(p, diff.getModeChanged().get(p),
                                                   diff.getTagsChanged().get(p),
                                                   diff.poolCost.get(p)));
        } finally {
            write.unlock();
        }
    }

    /**
     * <p>Called on dedicated thread.</p>
     *
     * <p>Does a diff under read lock.</p>
     *
     * <p>Gathers new pools, removed pools, new pool groups, removed pool
     *      groups, new storage units, removed storage units, modified groups
     *      and storage units, and pool information changes.</p>
     *
     * @param poolMonitor received from pool manager message.
     *
     * @return the diff (parsed out into relevant maps and collections).
     */
    public PoolInfoDiff compare(PoolMonitor poolMonitor) {
        read.lock();
        PoolSelectionUnit psu = poolMonitor.getPoolSelectionUnit();
        useRegex = psu.isEnabledRegex();
        PoolInfoDiff diff = new PoolInfoDiff();
        try {
            LOGGER.trace("Searching for currently uninitialized pools.");
            getUninitializedPools(diff);

            LOGGER.trace("comparing pools");
            Set<String> commonPools = comparePools(diff, psu);

            LOGGER.trace("comparing pool groups");
            Set<String> common = comparePoolGroups(diff, psu);

            LOGGER.trace("adding pools and units to new pool groups");
            addPoolsAndUnitsToNewPoolGroups(diff, psu);

            LOGGER.trace("comparing pools in pool groups");
            comparePoolsInPoolGroups(diff, common, psu);

            LOGGER.trace("comparing storage units");
            common = compareStorageUnits(diff, psu);

            LOGGER.trace("adding pool groups for new storage units");
            addPoolGroupsForNewUnits(diff, psu);

            LOGGER.trace("comparing storage unit links and constraints");
            compareStorageUnitLinksAndConstraints(diff, common, psu);

            LOGGER.trace("comparing pool info");
            comparePoolInfo(diff, commonPools, poolMonitor);
        } finally {
            read.unlock();
        }

        LOGGER.trace("Diff:\n{}", diff.toString());
        return diff;
    }


    public int getCountableLocations(Collection<String> locations) {
        read.lock();
        int countable = 0;
        try {
            for (String location : locations) {
                PoolInformation info = poolInfo.get(getPoolIndex(location));
                if (info != null && info.isInitialized() && info.isCountable()) {
                    ++countable;
                }
            }
        } finally {
            read.unlock();
        }
        return countable;
    }

    public Set<String> getExcludedLocationNames(Collection<String> members) {
        read.lock();
        try {
            return members.stream()
                          .map(l -> poolInfo.get(getPoolIndex(l)))
                          .filter(Objects::nonNull)
                          .filter(PoolInformation::isInitialized)
                          .filter(PoolInformation::isExcluded)
                          .map(PoolInformation::getName)
                          .collect(Collectors.toSet());
        } finally {
            read.unlock();
        }
    }


    public String getGroup(Integer group) {
        read.lock();
        try {
            return groups.get(group);
        } finally {
            read.unlock();
        }
    }

    public Integer getGroupIndex(String name) {
        read.lock();
        try {
            return groups.indexOf(name);
        } finally {
            read.unlock();
        }
    }

    public Set<String> getMemberLocations(Integer gindex,
                                          Collection<String> locations) {
        read.lock();
        try {
            Set<String> pools = getPools(getPoolsOfGroup(gindex));
            return locations.stream().filter(pools::contains)
                            .collect(Collectors.toSet());
        } finally {
            read.unlock();
        }
    }

    /**
     * @param writable location is writable if true, readable if false.
     * @return all pool group pools which qualify.
     */
    public Set<String> getMemberPools(Integer gindex, boolean writable) {
        read.lock();
        try {
            Set<Integer> members = ImmutableSet.copyOf(poolGroupToPool.get(gindex));
            members = getValidLocations(members, writable);
            return getPools(members);
        } finally {
            read.unlock();
        }
    }

    public String getPool(Integer pool) {
        read.lock();
        try {
            return pools.get(pool);
        } finally {
            read.unlock();
        }
    }

    public Collection<Integer> getPoolGroupsFor(String storageUnit) {
        Integer uindex = getUnitIndex(storageUnit);
        if (uindex == null) {
            return ImmutableList.of();
        }

        read.lock();
        try {
            return storageToPoolGroup.get(uindex);
        } finally {
            read.unlock();
        }
    }

    public Integer getPoolIndex(String name) {
        read.lock();
        try {
            return pools.indexOf(name);
        } finally {
            read.unlock();
        }
    }

    public Set<Integer> getPoolIndices(Collection<String> locations) {
        read.lock();
        try {
            return locations.stream()
                            .map(pools::indexOf)
                            .collect(Collectors.toSet());
        } finally {
            read.unlock();
        }
    }

    public PoolInformation getPoolInformation(Integer index) {
        read.lock();
        try {
            return poolInfo.get(index);
        } finally {
            read.unlock();
        }
    }

    public PoolManagerPoolInformation getPoolManagerInfo(Integer pool) {
        read.lock();
        try {
            return new PoolManagerPoolInformation(pools.get(pool),
                                                  poolInfo.get(pool).getCostInfo());
        } finally {
            read.unlock();
        }
    }

    public PoolStateUpdate getPoolState(String pool) {
        return getPoolState(pool, null, null, null);
    }

    public PoolStateUpdate getPoolState(String pool, String storageUnit) {
        return getPoolState(pool, null, null, storageUnit);
    }

    public PoolStateUpdate getPoolState(String pool, Integer addedTo,
                                        Integer removedFrom) {
        return getPoolState(pool, addedTo, removedFrom, null);
    }

    public PoolStateUpdate getPoolState(String pool, Integer addedTo,
                                        Integer removedFrom,
                                        String storageUnit) {
        PoolInformation info = getPoolInformation(getPoolIndex(pool));
        if (info != null) {
            return new PoolStateUpdate(pool, info.getMode(), addedTo,
                                       removedFrom, storageUnit);
        }

        /*
         * No information.  Treat it as UNINITIALIZED.
         */
        return new PoolStateUpdate(pool, null, addedTo, removedFrom, storageUnit);
    }

    public Set<String> getPools(Collection<Integer> indices) {
        read.lock();
        try {
            return indices.stream().map(pools::get).collect(Collectors.toSet());
        } finally {
            read.unlock();
        }
    }

    public Collection<Integer> getPoolsOfGroup(Integer group) {
        read.lock();
        try {
            return poolGroupToPool.get(group);
        } finally {
            read.unlock();
        }
    }

    public Set<String> getReadableLocations(Collection<String> locations) {
        read.lock();
        try {
            return locations.stream()
                            .filter((l) -> isPoolViable(getPoolIndex(l), false))
                            .collect(Collectors.toSet());
        } finally {
            read.unlock();
        }
    }

    public Integer getResilientPoolGroup(Integer pool) {
        read.lock();
        try {
            Set<Integer> rgroups
                = poolToPoolGroup.get(pool)
                                 .stream()
                                 .filter(this::isResilientGroup)
                                 .collect(Collectors.toSet());

            if (rgroups.size() == 0) {
                return null;
            }

            if (rgroups.size() > 1) {
                throw new IllegalStateException(String.format(
                                "Pool map is inconsistent; pool %s belongs to "
                                                + "more than one resilient "
                                                + "group: %s.",
                                pools.get(pool),
                                rgroups.stream()
                                       .map(groups::get)
                                       .collect(Collectors.toSet())));
            }

            return rgroups.iterator().next();
        } finally {
            read.unlock();
        }
    }

    public Set<String> getResilientPools() {
        read.lock();
        try {
            return pools.stream()
                        .filter(this::isResilientPool)
                        .collect(Collectors.toSet());
        } finally {
            read.unlock();
        }
    }

    public StorageUnitConstraints getStorageUnitConstraints(Integer unit) {
        return getConstraints(unit, constraints);
    }

    public Integer getStorageUnitIndex(FileAttributes attributes) {
        String classKey = attributes.getStorageClass();
        String unitKey = classKey;
        String hsm = attributes.getHsm();
        if (hsm != null) {
            unitKey += ("@" + hsm);
        }
        try {
            return getUnitIndex(unitKey);
        } catch (NoSuchElementException e) {
            return resolveStorageUnitIndex(classKey, unitKey);
        }
    }

    public Collection<Integer> getStorageUnitsFor(String poolGroup) {
        Integer gindex = getGroupIndex(poolGroup);
        if (gindex == null) {
            return ImmutableList.of();
        }

        read.lock();
        try {
            return poolGroupToStorage.get(gindex);
        } finally {
            read.unlock();
        }
    }

    public Map<String, String> getTags(Integer pool) {
        PoolInformation info = getPoolInformation(pool);
        if (info == null) {
            return ImmutableMap.of();
        }

        Map<String, String> tags = info.getTags();
        if (tags == null) {
            return ImmutableMap.of();
        }

        return tags;
    }

    public String getUnit(Integer index) {
        read.lock();
        try {
            return sunits.get(index);
        } finally {
            read.unlock();
        }
    }

    public Integer getUnitIndex(String name) {
        read.lock();
        try {
            return sunits.indexOf(name);
        } finally {
            read.unlock();
        }
    }

    public Set<Integer> getValidLocations(Collection<Integer> locations,
                                          boolean writable) {
        read.lock();
        try {
            return locations.stream()
                            .filter((i) -> isPoolViable(i, writable))
                            .collect(Collectors.toSet());
        } finally {
            read.unlock();
        }
    }

    public boolean hasPool(String pool) {
        read.lock();
        try {
            return pools.contains(pool);
        } finally {
            read.unlock();
        }
    }

    public boolean isValidPoolIndex(Integer index) {
        String pool = null;
        try {
            pool = getPool(index);
        } catch (NoSuchElementException e) {
        }
        return pool != null;
    }

    public boolean isPoolViable(Integer pool, boolean writable) {
        read.lock();
        try {
            PoolInformation info = poolInfo.get(pool);
            return info != null && info.isInitialized()
                            && (writable ? info.canRead() && info.canWrite()
                                : info.canRead());
        } finally {
            read.unlock();
        }
    }

    public boolean isResilientGroup(Integer gindex) {
        read.lock();
        try {
            return markers.get(gindex).isResilient();
        } finally {
            read.unlock();
        }
    }

    public boolean isResilientPool(String pool) {
        try {
            return getResilientPoolGroup(getPoolIndex(pool)) != null;
        } catch (NoSuchElementException e) {
            return false;
        }
    }

    public boolean isInitialized(String pool) {
        try {
            PoolInformation info = getPoolInformation(getPoolIndex(pool));
            return info != null && info.isInitialized();
        } catch (NoSuchElementException e) {
            return false;
        }
    }

    public String listPoolInfo(PoolInfoFilter poolInfoFilter) {
        final StringBuilder builder = new StringBuilder();
        read.lock();
        try {
            pools.stream()
                 .map(this::getPoolIndex)
                 .map(poolInfo::get)
                 .filter(poolInfoFilter::matches)
                 .forEach((i) -> builder.append(i).append("\n"));
        } finally {
            read.unlock();
        }
        return builder.toString();
    }

    /**
     * All unit tests are synchronous, so there is no need to lock
     * the map here.
     */
    @VisibleForTesting
    public void setUnitConstraints(String group, Integer required,
                                   Collection<String> oneCopyPer) {
        constraints.put(sunits.indexOf(group),
                        new StorageUnitConstraints(required, oneCopyPer));
    }

    public void updatePoolStatus(PoolStateUpdate update) {
        read.lock();
        try {
            poolInfo.get(pools.indexOf(update.pool)).updateState(update);
        } finally {
            read.unlock();
        }
    }

    /**
     * <p>A coarse-grained verification that the required and tag constraints
     *      of the pool group and its associated storage groups can be met.
     *      For the default and each storage unit, it attempts to fulfill the
     *      max independent location requirement via the
     *      {@link CopyLocationExtractor}.</p>
     *
     * @throws IllegalStateException upon encountering the first set of
     *                               constraints which cannot be met.
     */
    public void verifyConstraints(Integer pgindex)
                    throws IllegalStateException {
        Collection<Integer> storageGroups;
        CopyLocationExtractor extractor;

        read.lock();
        try {
            storageGroups = poolGroupToStorage.get(pgindex);
            for (Integer index : storageGroups) {
                StorageUnitConstraints unitConstraints
                                = (StorageUnitConstraints) constraints.get(index);
                int required = unitConstraints.getRequired();
                extractor = new CopyLocationExtractor(unitConstraints.getOneCopyPer(),
                                this);
                verify(pgindex, extractor, required);
            }
        } finally {
            read.unlock();
        }
    }

    /** Called under write lock **/
    private void addPoolGroup(SelectionPoolGroup group) {
        String name = group.getName();
        groups.add(name);
        markers.put(groups.indexOf(name),
                        new ResilienceMarker(group.isResilient()));
    }

    /** Called under write lock **/
    private void addPoolGroupsForNewUnits(PoolInfoDiff diff,
                                          PoolSelectionUnit psu) {
        Collection<StorageUnit> newUnits = diff.getNewUnits();
        for (StorageUnit unit : newUnits) {
            String name = unit.getName();
            StorageUnitInfoExtractor.getResilientGroupsFor(name, psu)
                                    .stream()
                                    .forEach((g) -> diff.unitsAdded.put(g, name));
        }
    }

    /** Called under write lock **/
    private void addPoolToPoolGroups(Entry<String, String> entry) {
        Integer pindex = pools.indexOf(entry.getKey());
        Integer gindex = groups.indexOf(entry.getValue());
        poolGroupToPool.put(gindex, pindex);
        poolToPoolGroup.put(pindex, gindex);
    }

    /** Called under write lock **/
    private void addPoolsAndUnitsToNewPoolGroups(PoolInfoDiff diff,
                                                 PoolSelectionUnit psu) {
        Collection<SelectionPoolGroup> newGroups = diff.getNewGroups();
        for (SelectionPoolGroup group : newGroups) {
            String name = group.getName();
            psu.getPoolsByPoolGroup(name)
               .stream()
               .map(SelectionPool::getName)
               .forEach((p) -> diff.poolsAdded.put(p, name));
            StorageUnitInfoExtractor.getStorageUnitsInGroup(name, psu)
               .stream()
               .forEach((u) -> diff.unitsAdded.put(name, u.getName()));
        }
    }

    /** Called under write lock **/
    private void addStorageUnit(StorageUnit unit) {
        String name = unit.getName();
        sunits.add(name);
        constraints.put(sunits.indexOf(name),
                        new StorageUnitConstraints(unit.getRequiredCopies(),
                                                   unit.getOnlyOneCopyPer()));
    }

    /** Called under write lock **/
    private void addUnitToPoolGroup(Entry<String, String> entry) {
        Integer gindex = groups.indexOf(entry.getKey());
        Integer sindex = sunits.indexOf(entry.getValue());
        storageToPoolGroup.put(sindex, gindex);
        poolGroupToStorage.put(gindex, sindex);
    }

    /** Called under read lock **/
    private Set<String> comparePoolGroups(PoolInfoDiff diff,
                                          PoolSelectionUnit psu) {
        Set<String> next = psu.getPoolGroups().values()
                                    .stream()
                                    .map(SelectionPoolGroup::getName)
                                    .collect(Collectors.toSet());
        Set<String> curr = poolGroupToPool.keySet()
                                    .stream()
                                    .map(this::getGroup)
                                    .collect(Collectors.toSet());
        Sets.difference(next, curr) .stream()
                                    .map((name) -> psu.getPoolGroups().get(name))
                                    .forEach(diff.newGroups::add);
        Sets.difference(curr, next) .stream()
                                    .forEach(diff.oldGroups::add);
        return Sets.intersection(next, curr);
    }

    /** Called under read lock **/
    private void comparePoolInfo(PoolInfoDiff diff, Set<String> commonPools,
                                 PoolMonitor poolMonitor) {
        PoolSelectionUnit psu = poolMonitor.getPoolSelectionUnit();
        CostModule costModule = poolMonitor.getCostModule();

        /*
         *  First add the info for all new pools to the diff.
         */
        diff.getNewPools().stream()
            .forEach((p) -> {
                diff.getModeChanged().put(p, getPoolMode(psu.getPool(p)));
                diff.getTagsChanged().put(p, getPoolTags(p, costModule));
                diff.getPoolCost().put(p, getPoolCostInfo(p, costModule));
            });

        /*
         * Now check for differences with current pools that are still valid.
         */
        commonPools.stream()
                   .forEach((p) -> {
                       PoolInformation info = poolInfo.get(getPoolIndex(p));
                       PoolV2Mode newMode = getPoolMode(psu.getPool(p));
                       PoolV2Mode oldMode = info.getMode();
                       if (oldMode == null || (newMode != null
                                       && !oldMode.equals(newMode))) {
                           diff.getModeChanged().put(p, newMode);
                       }

                       ImmutableMap<String, String> newTags
                                       = getPoolTags(p, costModule);
                       ImmutableMap<String, String> oldTags = info.getTags();
                       if (oldTags == null || (newTags != null
                                        && !oldTags.equals(newTags))) {
                           diff.getTagsChanged().put(p, newTags);
                       }

                       /*
                        * Since we are not altering the actual collections inside
                        * the PoolInfoMap, but are simply modifying the PoolInformation
                        * object, and since its own update method is synchronized,
                        * we can take care of the update here while holding a read lock.
                        */
                       info.update(newMode, newTags, getPoolCostInfo(p, costModule));
                   });

    }

    /** Called under read lock **/
    private Set<String> comparePools(PoolInfoDiff diff,
                              PoolSelectionUnit psu) {
        Set<String> next = psu.getPools().values()
                              .stream()
                              .map(SelectionPool::getName)
                              .collect(Collectors.toSet());
        Set<String> curr = ImmutableSet.copyOf(pools);
        Sets.difference(next, curr).stream().forEach(diff.newPools::add);
        Sets.difference(curr, next).stream().forEach(diff.oldPools::add);
        return Sets.intersection(curr, next);
    }

    /** Called under read lock **/
    private void comparePoolsInPoolGroups(PoolInfoDiff diff,
                                          Set<String> common,
                                          PoolSelectionUnit psu) {
        for (String group : common) {
            Set<String> next = psu.getPoolsByPoolGroup(group)
                                  .stream()
                                  .map(SelectionPool::getName)
                                  .collect(Collectors.toSet());
            Set<String> curr = poolGroupToPool.get(groups.indexOf(group))
                                              .stream()
                                              .map(this::getPool)
                                              .collect(Collectors.toSet());
            Sets.difference(next, curr)
                .stream()
                .forEach((p) -> diff.poolsAdded.put(p, group));
            Sets.difference(curr, next)
                .stream()
                .filter((p) -> !diff.oldPools.contains(p))
                .forEach((p) -> diff.poolsRmved.put(p, group));
        }
    }

    /** Called under read lock **/
    private void compareStorageUnitLinksAndConstraints(PoolInfoDiff diff,
                                                       Set<String> common,
                                                       PoolSelectionUnit psu) {
        for (String unit : common) {
            StorageUnit storageUnit = psu.getStorageUnit(unit);
            int index = sunits.indexOf(unit);
            Set<String> next = ImmutableSet
                            .copyOf(StorageUnitInfoExtractor
                                                    .getPoolGroupsFor(unit,
                                                                      psu,
                                                                      false));
            Set<String> curr = storageToPoolGroup.get(index)
                                                 .stream()
                                                 .map(this::getGroup)
                                                 .collect(Collectors.toSet());
            Sets.difference(next, curr)
                .stream()
                .forEach((group) -> diff.unitsAdded.put(group, unit));
            Sets.difference(curr, next)
                .stream()
                .filter((group) -> !diff.oldGroups.contains(group))
                .forEach((group) -> diff.unitsRmved.put(group, unit));

            int required = storageUnit.getRequiredCopies();
            Set<String> oneCopyPer
                            = ImmutableSet.copyOf(storageUnit.getOnlyOneCopyPer());
            StorageUnitConstraints constraints
                            = (StorageUnitConstraints) this.constraints.get(index);
            if (required != constraints.getRequired() ||
                            !oneCopyPer.equals(constraints.getOneCopyPer())) {
                diff.constraints.put(unit,
                                     new StorageUnitConstraints(required,
                                                                oneCopyPer));
            }
        }
    }

    /** Called under read lock **/
    private Set<String> compareStorageUnits(PoolInfoDiff diff,
                                            PoolSelectionUnit psu) {
        Set<String> next = psu.getSelectionUnits().values()
                                .stream()
                                .filter(StorageUnit.class::isInstance)
                                .map(SelectionUnit::getName)
                                .collect(Collectors.toSet());
        Set<String> curr = storageToPoolGroup.keySet()
                                .stream()
                                .map(this::getUnit)
                                .collect(Collectors.toSet());
        Sets.difference(next, curr)
                                .stream()
                                .map(psu::getStorageUnit)
                                .forEach(diff.newUnits::add);
        Sets.difference(curr, next)
                                .stream().forEach( diff.oldUnits::add);
        return Sets.intersection(next, curr);
    }

    private PoolV2Mode getPoolMode(SelectionPool pool) {
        /*
         *  Allow a NULL value
         */
        return pool.getPoolMode();
    }

    private ImmutableMap<String, String> getPoolTags(String pool,
                                                     CostModule costModule) {
        PoolInfo poolInfo = costModule.getPoolInfo(pool);
        if (poolInfo == null) {
            return null;
        }
        return poolInfo.getTags();
    }

    private PoolCostInfo getPoolCostInfo(String pool, CostModule costModule) {
        /*
         *  Allow a NULL value
         */
        return costModule.getPoolCostInfo(pool);
    }

    private void getUninitializedPools(PoolInfoDiff diff) {
        pools.stream()
             .filter((p) -> !isInitialized(p))
             .forEach(diff.uninitPools::add);
    }

    /** Called under write lock **/
    private void removeFromPoolGroup(Entry<String, String> entry) {
        Integer pindex = pools.indexOf(entry.getKey());
        Integer gindex = groups.indexOf(entry.getValue());
        poolGroupToPool.remove(gindex, pindex);
        poolToPoolGroup.remove(pindex, gindex);
    }

    /** Called under write lock **/
    private void removeGroup(String group) {
        int index = groups.indexOf(group);
        groups.remove(index);
        markers.remove(index);
        poolGroupToPool.removeAll(index)
                       .stream()
                       .forEach((pindex) -> poolToPoolGroup.remove(pindex,
                                                                   index));
        poolGroupToStorage.removeAll(index)
                          .stream()
                          .forEach((gindex) -> storageToPoolGroup.remove(
                                          gindex, index));
    }

    /** Called under write lock **/
    private void removePool(String pool) {
        int pindex = getPoolIndex(pool);
        pools.remove(pindex);
        poolToPoolGroup.removeAll(pindex).stream()
                       .forEach((g) ->poolGroupToPool.remove(g, pindex));
        poolInfo.remove(pindex);
    }

    /** Called under write lock **/
    private void removeUnit(String unit) {
        int index = sunits.indexOf(unit);
        sunits.remove(index);
        constraints.remove(index);
        storageToPoolGroup.removeAll(index).stream()
                          .forEach((gindex) -> poolGroupToStorage.remove(gindex, index));
    }

    /** Called under write lock **/
    private void removeStorageUnit(Entry<String, String> entry) {
        Integer sindex = sunits.indexOf(entry.getValue());
        Integer pindex = groups.indexOf(entry.getKey());
        storageToPoolGroup.remove(sindex, pindex);
        poolGroupToStorage.remove(pindex, sindex);
    }


    /**
     * <p>This method is an alternate search for storage unit.
     *    It first attempts to match units by interpreting the
     *    class names as a regex. If that fails, it tries
     *    first the class key, then universal key.</p>
     *
     * @param classKey the storage class of the unit
     * @param unitKey  the full name of the storage unit
     */
    private Integer resolveStorageUnitIndex(String classKey, String unitKey)
                    throws NoSuchElementException {
        Integer universalCoverage = null;
        Integer classCoverage = null;
        Integer specific = null;

        read.lock();
        try {
            for (String unit : sunits) {
                if (unit.equals("*@*")) {
                    universalCoverage = sunits.indexOf(unit);
                } else if (unit.equals("*@" + classKey)) {
                    classCoverage = sunits.indexOf(unit);
                } else if (useRegex && Pattern.matches(unit, unitKey)) {
                    specific = sunits.indexOf(unit);
                    break;
                }
            }
        } finally {
            read.unlock();
        }

        if (specific != null) {
            return specific;
        }

        if (classCoverage != null) {
            return classCoverage;
        }

        if (universalCoverage != null) {
            return universalCoverage;
        }

        /*
         *  Preserve behavior of the NonReindexable list
         */
        throw new NoSuchElementException(String.valueOf(unitKey));
    }

    /** Called under write lock **/
    private void setPoolInfo(String pool,
                             PoolV2Mode mode,
                             ImmutableMap<String, String> tags,
                             PoolCostInfo cost) {
        Integer pindex = pools.indexOf(pool);
        PoolInformation entry = new PoolInformation(pool, pindex);
        entry.update(mode, tags, cost);
        poolInfo.put(pindex, entry);
    }

    /** Called under write lock **/
    private void updateConstraints(Entry<String, StorageUnitConstraints> entry) {
        constraints.put(sunits.indexOf(entry.getKey()), entry.getValue());
    }

    /**
     * Called under read lock
     *
     * @param index     of pool group.
     * @param extractor configured for the specific tag constraints.
     * @param required  specific to this group or storage unit.
     * @throws IllegalStateException upon encountering the first set of
     *                               constraints which cannot be met.
     */
    private void verify(Integer index,
                        CopyLocationExtractor extractor,
                        int required) throws IllegalStateException {
        Set<String> members = poolGroupToPool.get(index).stream()
                                     .map(pools::get)
                                     .collect(Collectors.toSet());
        for (int i = 0; i < required; i++) {
            Collection<String> candidates
                            = extractor.getCandidateLocations(members);
            if (candidates.isEmpty()) {
                throw new IllegalStateException(getGroup(index));
            }
            String selected = RandomSelectionStrategy.SELECTOR.apply(candidates);
            members.remove(selected);
            extractor.addSeenTagsFor(selected);
        }
    }
}