opendaylight/md-sal/sal-distributed-eos/src/main/java/org/opendaylight/controller/cluster/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.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(final long selectionDelayInMillis,
  26             final Map<String, Long> initialStatistics) {
  27         super(selectionDelayInMillis, initialStatistics);
  28
  29         localStatistics.putAll(initialStatistics);
  30     }
  31
  32     @Override
  33     public String newOwner(final String currentOwner, final Collection<String> viableCandidates) {
  34         Preconditions.checkArgument(viableCandidates.size() > 0);
  35         String leastLoadedCandidate = null;
  36         long leastLoadedCount = Long.MAX_VALUE;
  37
  38         if (!Strings.isNullOrEmpty(currentOwner)) {
  39             long localVal = MoreObjects.firstNonNull(localStatistics.get(currentOwner), 0L);
  40             localStatistics.put(currentOwner, localVal - 1);
  41         }
  42
  43         for (String candidateName : viableCandidates) {
  44             long val = MoreObjects.firstNonNull(localStatistics.get(candidateName), 0L);
  45             if (val < leastLoadedCount) {
  46                 leastLoadedCount = val;
  47                 leastLoadedCandidate = candidateName;
  48             }
  49         }
  50
  51         if (leastLoadedCandidate == null) {
  52             leastLoadedCandidate = viableCandidates.iterator().next();
  53         }
  54
  55         localStatistics.put(leastLoadedCandidate, leastLoadedCount + 1);
  56         return leastLoadedCandidate;
  57     }
  58
  59     @VisibleForTesting
  60     Map<String, Long> getLocalStatistics() {
  61         return localStatistics;
  62     }
  63 }