/*
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* CDDL HEADER START
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*
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* The contents of this file are subject to the terms of the
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* Common Development and Distribution License, Version 1.0 only
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* (the "License"). You may not use this file except in compliance
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* with the License.
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*
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* You can obtain a copy of the license at legal-notices/CDDLv1_0.txt
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* or http://forgerock.org/license/CDDLv1.0.html.
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* See the License for the specific language governing permissions
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* and limitations under the License.
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*
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* When distributing Covered Code, include this CDDL HEADER in each
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* file and include the License file at legal-notices/CDDLv1_0.txt.
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* If applicable, add the following below this CDDL HEADER, with the
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* fields enclosed by brackets "[]" replaced with your own identifying
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* information:
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* Portions Copyright [yyyy] [name of copyright owner]
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*
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* CDDL HEADER END
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*
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*
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* Copyright 2010 Sun Microsystems, Inc.
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* Portions copyright 2013 ForgeRock AS.
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*/
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package org.forgerock.opendj.ldap;
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import java.util.Collection;
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import java.util.concurrent.ScheduledExecutorService;
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import java.util.concurrent.TimeUnit;
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import java.util.concurrent.atomic.AtomicInteger;
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/**
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* A round robin load balancing algorithm distributes connection requests across
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* a list of connection factories one at a time. When the end of the list is
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* reached, the algorithm starts again from the beginning.
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* <p>
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* This algorithm is typically used for load-balancing <i>within</i> data
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* centers, where load must be distributed equally across multiple data sources.
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* This algorithm contrasts with the {@link FailoverLoadBalancingAlgorithm}
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* which is used for load-balancing <i>between</i> data centers.
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* <p>
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* If a problem occurs that temporarily prevents connections from being obtained
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* for one of the connection factories, then this algorithm automatically
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* "fails over" to the next operational connection factory in the list. If none
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* of the connection factories are operational then a
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* {@code ConnectionException} is returned to the client.
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* <p>
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* The implementation periodically attempts to connect to failed connection
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* factories in order to determine if they have become available again.
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*
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* @see FailoverLoadBalancingAlgorithm
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* @see Connections#newLoadBalancer(LoadBalancingAlgorithm)
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*/
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public final class RoundRobinLoadBalancingAlgorithm extends AbstractLoadBalancingAlgorithm {
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private final int maxIndex;
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private final AtomicInteger nextIndex = new AtomicInteger(-1);
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/**
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* Creates a new round robin load balancing algorithm which will monitor
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* offline connection factories every 1 second using the default scheduler.
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*
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* @param factories
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* The ordered collection of connection factories.
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*/
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public RoundRobinLoadBalancingAlgorithm(final Collection<ConnectionFactory> factories) {
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this(factories, null, 1, TimeUnit.SECONDS, null);
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}
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/**
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* Creates a new round robin load balancing algorithm which will monitor
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* offline connection factories every 1 second using the default scheduler.
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*
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* @param factories
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* The ordered collection of connection factories.
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* @param listener
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* The event listener which should be notified whenever a
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* connection factory changes state from online to offline or
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* vice-versa.
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*/
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public RoundRobinLoadBalancingAlgorithm(final Collection<ConnectionFactory> factories,
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final LoadBalancerEventListener listener) {
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this(factories, listener, 1, TimeUnit.SECONDS, null);
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}
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/**
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* Creates a new round robin load balancing algorithm which will monitor
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* offline connection factories using the specified frequency using the
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* default scheduler.
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*
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* @param factories
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* The connection factories.
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* @param listener
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* The event listener which should be notified whenever a
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* connection factory changes state from online to offline or
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* vice-versa.
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* @param interval
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* The interval between attempts to poll offline factories.
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* @param unit
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* The time unit for the interval between attempts to poll
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* offline factories.
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*/
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public RoundRobinLoadBalancingAlgorithm(final Collection<ConnectionFactory> factories,
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final LoadBalancerEventListener listener, final long interval, final TimeUnit unit) {
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this(factories, null, interval, unit, null);
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}
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/**
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* Creates a new round robin load balancing algorithm which will monitor
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* offline connection factories using the specified frequency and scheduler.
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*
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* @param factories
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* The connection factories.
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* @param listener
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* The event listener which should be notified whenever a
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* connection factory changes state from online to offline or
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* vice-versa.
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* @param interval
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* The interval between attempts to poll offline factories.
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* @param unit
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* The time unit for the interval between attempts to poll
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* offline factories.
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* @param scheduler
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* The scheduler which should for periodically monitoring dead
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* connection factories to see if they are usable again.
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*/
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public RoundRobinLoadBalancingAlgorithm(final Collection<ConnectionFactory> factories,
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final LoadBalancerEventListener listener, final long interval, final TimeUnit unit,
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final ScheduledExecutorService scheduler) {
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super(factories, listener, interval, unit, scheduler);
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this.maxIndex = factories.size();
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}
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/**
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* Creates a new round robin load balancing algorithm which will monitor
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* offline connection factories using the specified frequency using the
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* default scheduler.
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*
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* @param factories
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* The connection factories.
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* @param interval
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* The interval between attempts to poll offline factories.
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* @param unit
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* The time unit for the interval between attempts to poll
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* offline factories.
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*/
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public RoundRobinLoadBalancingAlgorithm(final Collection<ConnectionFactory> factories,
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final long interval, final TimeUnit unit) {
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this(factories, null, interval, unit, null);
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}
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/**
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* Creates a new round robin load balancing algorithm which will monitor
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* offline connection factories using the specified frequency and scheduler.
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*
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* @param factories
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* The connection factories.
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* @param interval
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* The interval between attempts to poll offline factories.
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* @param unit
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* The time unit for the interval between attempts to poll
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* offline factories.
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* @param scheduler
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* The scheduler which should for periodically monitoring dead
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* connection factories to see if they are usable again.
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*/
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public RoundRobinLoadBalancingAlgorithm(final Collection<ConnectionFactory> factories,
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final long interval, final TimeUnit unit, final ScheduledExecutorService scheduler) {
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this(factories, null, interval, unit, scheduler);
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}
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/**
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* {@inheritDoc}
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*/
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@Override
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String getAlgorithmName() {
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return "RoundRobin";
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}
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/**
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* {@inheritDoc}
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*/
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@Override
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int getInitialConnectionFactoryIndex() {
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// A round robin pool of one connection factories is unlikely in
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// practice and requires special treatment.
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if (maxIndex == 1) {
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return 0;
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}
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// Determine the next factory to use: avoid blocking algorithm.
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int oldNextIndex;
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int newNextIndex;
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do {
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oldNextIndex = nextIndex.get();
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newNextIndex = oldNextIndex + 1;
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if (newNextIndex == maxIndex) {
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newNextIndex = 0;
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}
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} while (!nextIndex.compareAndSet(oldNextIndex, newNextIndex));
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// There's a potential, but benign, race condition here: other threads
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// could jump in and rotate through the list before we return the
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// connection factory.
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return newNextIndex;
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}
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}
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