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package org.dcache.resilience.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;
/**
* <p>Implementation of the {@link PoolTagConstraintDiscriminator} which returns
* a list containing the pools or 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 pool1 has tag1 with value A and
* tag2 with value X, and A is shared by 3 other pools and X by 2, then
* pool1 has a weight of 5.</p>
*
* <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 for
* replication. First, it will add the tags of all current replica 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 PoolTagConstraintDiscriminator {
protected final Multimap<String, String> seenTags = HashMultimap.create();
protected AbstractLocationExtractor(Collection<String> onlyOneCopyPer) {
super(onlyOneCopyPer);
}
/**
* <p>Add tag names and values for the location/pool
* to the map of seen tags.</p>
*
* @param location which has been selected.
*/
public void addSeenTagsFor(String location) {
Map<String, String> tags = getPoolTagsFor(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 = getPoolTagsFor(location);
/*
* An "undefined" situation. For maximum flexibility,
* we allow the pool 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 pool.
*/
if (tagValue == null) {
continue;
}
Collection<String> values = seenTags.get(tagName);
if (values != null && values.contains(tagValue)) {
++violations;
}
}
return violations;
}
}