AbstractLocationExtractor.java

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package org.dcache.qos.services.verifier.util;

import com.google.common.collect.HashMultimap;
import com.google.common.collect.Multimap;
import java.util.Collection;
import java.util.Map;
import java.util.stream.Collectors;

/**
 * Implementation of the {@link ConstraintDiscriminator} which returns a list containing the
 * locations with zero weight.  The weights are computed in terms of the sum of the size of the
 * value partitions to which they belong.  For instance, if location1 has tag1 with value A and tag2
 * with value X, and A is shared by 3 other locations and X by 2, then location1 has a weight of 5.
 * <p/>
 * The use case envisaged here is as follows:  the component has a set of available locations from
 * which it must choose one or more. First, it will add the tags of all current locations to the
 * seenTags map. It will then run getCandidateLocations() on the list one or more times, each time
 * picking a location from the returned list using some selection algorithm, removing this location
 * from the available list and adding its tags to the seenTags map, and finally passing the modified
 * available list in to any further iteration.</p>
 */
public abstract class AbstractLocationExtractor extends ConstraintDiscriminator {

    protected final Multimap<String, String> seenTags = HashMultimap.create();

    protected AbstractLocationExtractor(Collection<String> onlyOneCopyPer) {
        super(onlyOneCopyPer);
    }

    /**
     * Add tag names and values for the location/pool to the map of seen tags.
     *
     * @param location which has been selected.
     */
    public void addSeenTagsFor(String location) {
        Map<String, String> tags = getKeyValuesFor(location);

        if (tags == null || tags.isEmpty()) {
            return;
        }

        for (String tagName : partitionKeys) {
            String tagValue = tags.get(tagName);

            if (tagValue == null) {
                continue;
            }

            seenTags.put(tagName, tagValue);
        }
    }

    @Override
    public Collection<String> getCandidateLocations(Collection<String> locations) {
        return locations.stream().filter((l) -> checkPartitionConstraints(l) == 0)
              .collect(Collectors.toList());
    }

    public void reset() {
        seenTags.clear();
    }

    /**
     * @param location to examine
     * @return the number of tags whose values match values already stored in the seenTags map --
     * that is, of locations/pools which either already exist or have been selected.
     */
    private int checkPartitionConstraints(String location) {
        Map<String, String> tags = getKeyValuesFor(location);

        /*
         *  An "undefined" situation.
         *  For maximum flexibility, we allow the location to be selected.
         */
        if (tags == null || tags.isEmpty()) {
            return 0;
        }

        int violations = 0;

        for (String tagName : partitionKeys) {
            String tagValue = tags.get(tagName);

            /*
             *  Again, this is an "undefined" situation, so
             *  we provisionally qualify the location.
             */
            if (tagValue == null) {
                continue;
            }

            Collection<String> values = seenTags.get(tagName);

            if (values != null && values.contains(tagValue)) {
                ++violations;
            }
        }

        return violations;
    }
}