opendaylight/md-sal/sal-distributed-datastore/src/main/java/org/opendaylight/controller/cluster/datastore/entityownership/selectionstrategy/LeastLoadedCandidateSelectionStrategy.java

   1 /*
   2  * Copyright (c) 2015 Cisco Systems, Inc. and others.  All rights reserved.
   3  *
   4  * This program and the accompanying materials are made available under the
   5  * terms of the Eclipse Public License v1.0 which accompanies this distribution,
   6  * and is available at http://www.eclipse.org/legal/epl-v10.html
   7  */
   8 package org.opendaylight.controller.cluster.datastore.entityownership.selectionstrategy;
   9
  10 import com.google.common.annotations.VisibleForTesting;
  11 import com.google.common.base.MoreObjects;
  12 import com.google.common.base.Preconditions;
  13 import com.google.common.base.Strings;
  14 import java.util.Collection;
  15 import java.util.HashMap;
  16 import java.util.Map;
  17
  18 /**
  19  * The LeastLoadedCandidateSelectionStrategy assigns ownership for an entity to the candidate which owns the least
  20  * number of entities.
  21  */
  22 public class LeastLoadedCandidateSelectionStrategy extends AbstractEntityOwnerSelectionStrategy {
  23     private final Map<String, Long> localStatistics = new HashMap<>();
  24
  25     protected LeastLoadedCandidateSelectionStrategy(long selectionDelayInMillis, Map<String, Long> initialStatistics) {
  26         super(selectionDelayInMillis, initialStatistics);
  27
  28         localStatistics.putAll(initialStatistics);
  29     }
  30
  31     @Override
  32     public String newOwner(String currentOwner, Collection<String> viableCandidates) {
  33         Preconditions.checkArgument(viableCandidates.size() > 0);
  34         String leastLoadedCandidate = null;
  35         long leastLoadedCount = Long.MAX_VALUE;
  36
  37         if (!Strings.isNullOrEmpty(currentOwner)) {
  38             long localVal = MoreObjects.firstNonNull(localStatistics.get(currentOwner), 0L);
  39             localStatistics.put(currentOwner, localVal - 1);
  40         }
  41
  42         for (String candidateName : viableCandidates) {
  43             long val = MoreObjects.firstNonNull(localStatistics.get(candidateName), 0L);
  44             if (val < leastLoadedCount) {
  45                 leastLoadedCount = val;
  46                 leastLoadedCandidate = candidateName;
  47             }
  48         }
  49
  50         if (leastLoadedCandidate == null) {
  51             leastLoadedCandidate = viableCandidates.iterator().next();
  52         }
  53
  54         localStatistics.put(leastLoadedCandidate, leastLoadedCount + 1);
  55         return leastLoadedCandidate;
  56     }
  57
  58     @VisibleForTesting
  59     Map<String, Long> getLocalStatistics() {
  60         return localStatistics;
  61     }
  62 }