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 edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
  16 import java.util.Collection;
  17 import java.util.HashMap;
  18 import java.util.Map;
  19 import javax.annotation.Nullable;
  20
  21 /**
  22  * The LeastLoadedCandidateSelectionStrategy assigns ownership for an entity to the candidate which owns the least
  23  * number of entities.
  24  */
  25 public class LeastLoadedCandidateSelectionStrategy extends AbstractEntityOwnerSelectionStrategy {
  26     private final Map<String, Long> localStatistics = new HashMap<>();
  27
  28     protected LeastLoadedCandidateSelectionStrategy(long selectionDelayInMillis, Map<String, Long> initialStatistics) {
  29         super(selectionDelayInMillis, initialStatistics);
  30
  31         localStatistics.putAll(initialStatistics);
  32     }
  33
  34     @Override
  35     @SuppressFBWarnings(value = "NP_PARAMETER_MUST_BE_NONNULL_BUT_MARKED_AS_NULLABLE",
  36             justification = "Unrecognised NullableDecl")
  37     public String newOwner(@Nullable String currentOwner, Collection<String> viableCandidates) {
  38         Preconditions.checkArgument(viableCandidates.size() > 0);
  39         String leastLoadedCandidate = null;
  40         long leastLoadedCount = Long.MAX_VALUE;
  41
  42         if (!Strings.isNullOrEmpty(currentOwner)) {
  43             long localVal = MoreObjects.firstNonNull(localStatistics.get(currentOwner), 0L);
  44             localStatistics.put(currentOwner, localVal - 1);
  45         }
  46
  47         for (String candidateName : viableCandidates) {
  48             long val = MoreObjects.firstNonNull(localStatistics.get(candidateName), 0L);
  49             if (val < leastLoadedCount) {
  50                 leastLoadedCount = val;
  51                 leastLoadedCandidate = candidateName;
  52             }
  53         }
  54
  55         if (leastLoadedCandidate == null) {
  56             leastLoadedCandidate = viableCandidates.iterator().next();
  57         }
  58
  59         localStatistics.put(leastLoadedCandidate, leastLoadedCount + 1);
  60         return leastLoadedCandidate;
  61     }
  62
  63     @VisibleForTesting
  64     Map<String, Long> getLocalStatistics() {
  65         return localStatistics;
  66     }
  67 }