RoundRobinLoadBalancingAlgorithm.java revision 6870993d12bf8a2b9d5cd103dc5ccabc42f9bf5d
/*
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* Copyright 2010 Sun Microsystems, Inc.
* Portions copyright 2013 ForgeRock AS.
*/
package org.forgerock.opendj.ldap;
import java.util.Collection;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
/**
* A round robin load balancing algorithm distributes connection requests across
* a list of connection factories one at a time. When the end of the list is
* reached, the algorithm starts again from the beginning.
* <p>
* This algorithm is typically used for load-balancing <i>within</i> data
* centers, where load must be distributed equally across multiple data sources.
* This algorithm contrasts with the {@link FailoverLoadBalancingAlgorithm}
* which is used for load-balancing <i>between</i> data centers.
* <p>
* If a problem occurs that temporarily prevents connections from being obtained
* for one of the connection factories, then this algorithm automatically
* "fails over" to the next operational connection factory in the list. If none
* of the connection factories are operational then a
* {@code ConnectionException} is returned to the client.
* <p>
* The implementation periodically attempts to connect to failed connection
* factories in order to determine if they have become available again.
*
* @see FailoverLoadBalancingAlgorithm
* @see Connections#newLoadBalancer(LoadBalancingAlgorithm)
*/
public final class RoundRobinLoadBalancingAlgorithm extends AbstractLoadBalancingAlgorithm {
private final int maxIndex;
private final AtomicInteger nextIndex = new AtomicInteger(-1);
/**
* Creates a new round robin load balancing algorithm which will monitor
* offline connection factories every 1 second using the default scheduler.
*
* @param factories
* The ordered collection of connection factories.
*/
public RoundRobinLoadBalancingAlgorithm(final Collection<? extends ConnectionFactory> factories) {
this(factories, null, 1, TimeUnit.SECONDS, null);
}
/**
* Creates a new round robin load balancing algorithm which will monitor
* offline connection factories every 1 second using the default scheduler.
*
* @param factories
* The ordered collection of connection factories.
* @param listener
* The event listener which should be notified whenever a
* connection factory changes state from online to offline or
* vice-versa.
*/
public RoundRobinLoadBalancingAlgorithm(
final Collection<? extends ConnectionFactory> factories,
final LoadBalancerEventListener listener) {
this(factories, listener, 1, TimeUnit.SECONDS, null);
}
/**
* Creates a new round robin load balancing algorithm which will monitor
* offline connection factories using the specified frequency using the
* default scheduler.
*
* @param factories
* The connection factories.
* @param listener
* The event listener which should be notified whenever a
* connection factory changes state from online to offline or
* vice-versa.
* @param interval
* The interval between attempts to poll offline factories.
* @param unit
* The time unit for the interval between attempts to poll
* offline factories.
*/
public RoundRobinLoadBalancingAlgorithm(
final Collection<? extends ConnectionFactory> factories,
final LoadBalancerEventListener listener, final long interval, final TimeUnit unit) {
this(factories, null, interval, unit, null);
}
/**
* Creates a new round robin load balancing algorithm which will monitor
* offline connection factories using the specified frequency and scheduler.
*
* @param factories
* The connection factories.
* @param listener
* The event listener which should be notified whenever a
* connection factory changes state from online to offline or
* vice-versa.
* @param interval
* The interval between attempts to poll offline factories.
* @param unit
* The time unit for the interval between attempts to poll
* offline factories.
* @param scheduler
* The scheduler which should for periodically monitoring dead
* connection factories to see if they are usable again.
*/
public RoundRobinLoadBalancingAlgorithm(
final Collection<? extends ConnectionFactory> factories,
final LoadBalancerEventListener listener, final long interval, final TimeUnit unit,
final ScheduledExecutorService scheduler) {
super(factories, listener, interval, unit, scheduler);
this.maxIndex = factories.size();
}
/**
* Creates a new round robin load balancing algorithm which will monitor
* offline connection factories using the specified frequency using the
* default scheduler.
*
* @param factories
* The connection factories.
* @param interval
* The interval between attempts to poll offline factories.
* @param unit
* The time unit for the interval between attempts to poll
* offline factories.
*/
public RoundRobinLoadBalancingAlgorithm(
final Collection<? extends ConnectionFactory> factories, final long interval,
final TimeUnit unit) {
this(factories, null, interval, unit, null);
}
/**
* Creates a new round robin load balancing algorithm which will monitor
* offline connection factories using the specified frequency and scheduler.
*
* @param factories
* The connection factories.
* @param interval
* The interval between attempts to poll offline factories.
* @param unit
* The time unit for the interval between attempts to poll
* offline factories.
* @param scheduler
* The scheduler which should for periodically monitoring dead
* connection factories to see if they are usable again.
*/
public RoundRobinLoadBalancingAlgorithm(
final Collection<? extends ConnectionFactory> factories, final long interval,
final TimeUnit unit, final ScheduledExecutorService scheduler) {
this(factories, null, interval, unit, scheduler);
}
/** {@inheritDoc} */
@Override
String getAlgorithmName() {
return "RoundRobin";
}
/** {@inheritDoc} */
@Override
int getInitialConnectionFactoryIndex() {
// A round robin pool of one connection factories is unlikely in
// practice and requires special treatment.
if (maxIndex == 1) {
return 0;
}
// Determine the next factory to use: avoid blocking algorithm.
int oldNextIndex;
int newNextIndex;
do {
oldNextIndex = nextIndex.get();
newNextIndex = oldNextIndex + 1;
if (newNextIndex == maxIndex) {
newNextIndex = 0;
}
} while (!nextIndex.compareAndSet(oldNextIndex, newNextIndex));
// There's a potential, but benign, race condition here: other threads
// could jump in and rotate through the list before we return the
// connection factory.
return newNextIndex;
}
}