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
   9 package org.opendaylight.controller.cluster.datastore.entityownership.selectionstrategy;
  10
  11 import com.google.common.annotations.VisibleForTesting;
  12 import com.google.common.base.MoreObjects;
  13 import com.google.common.base.Preconditions;
  14 import com.google.common.base.Strings;
  15 import java.util.Collection;
  16 import java.util.HashMap;
  17 import java.util.Map;
  18 import javax.annotation.Nullable;
  19
  20 /**
  21  * The LeastLoadedCandidateSelectionStrategy assigns ownership for an entity to the candidate which owns the least
  22  * number of entities.
  23  */
  24 public class LeastLoadedCandidateSelectionStrategy extends AbstractEntityOwnerSelectionStrategy {
  25     private final Map<String, Long> localStatistics = new HashMap<>();
  26
  27     protected LeastLoadedCandidateSelectionStrategy(long selectionDelayInMillis, Map<String, Long> initialStatistics) {
  28         super(selectionDelayInMillis, initialStatistics);
  29
  30         localStatistics.putAll(initialStatistics);
  31     }
  32
  33     @Override
  34     public String newOwner(@Nullable String currentOwner, Collection<String> viableCandidates) {
  35         Preconditions.checkArgument(viableCandidates.size() > 0);
  36         String leastLoadedCandidate = null;
  37         long leastLoadedCount = Long.MAX_VALUE;
  38
  39         if (!Strings.isNullOrEmpty(currentOwner)) {
  40             long localVal = MoreObjects.firstNonNull(localStatistics.get(currentOwner), 0L);
  41             localStatistics.put(currentOwner, localVal - 1);
  42         }
  43
  44         for (String candidateName : viableCandidates) {
  45             long val = MoreObjects.firstNonNull(localStatistics.get(candidateName), 0L);
  46             if (val < leastLoadedCount) {
  47                 leastLoadedCount = val;
  48                 leastLoadedCandidate = candidateName;
  49             }
  50         }
  51
  52         if (leastLoadedCandidate == null) {
  53             leastLoadedCandidate = viableCandidates.iterator().next();
  54         }
  55
  56         localStatistics.put(leastLoadedCandidate, leastLoadedCount + 1);
  57         return leastLoadedCandidate;
  58     }
  59
  60     @VisibleForTesting
  61     Map<String, Long> getLocalStatistics() {
  62         return localStatistics;
  63     }
  64 }