jrunx.cluster
Class ClusterAlgorithm

java.lang.Object
  |
  +--jrunx.cluster.ClusterAlgorithm

All Implemented Interfaces:

ClusterConstants, java.io.Serializable

Direct Known Subclasses:

AbstractBuddyAlgorithm, InvocationAlgorithm, RoundRobinAlgorithm

public abstract class ClusterAlgorithm

extends java.lang.Object

implements ClusterConstants, java.io.Serializable

This abstract class represents the base algorithm used in selecting a stub for clustering. At minimum, subclasses must override the selectService(ArrayList services) method.
When a RemoteInvocationHandler or other invoker of clusterable services uses an algorithm, it invokes the invokeService(Invocation inv) method. This causes the algorithm to first select a service using the selectService(ArrayList services) method, in which an algorithm can use its own specific means of choosing a ClusterableService from the list of available services. After selecting the service, the invokeService(Invocation inv, ClusterableService svc) method is invoked, where svc denotes the selected service. The method is invoked on the chosen service, and if an Exception occurs it is checked to see whether it is recoverable (based on ClusterException.isReinvokable(...)). If it is recoverable, a new service is selected and the method is re-invoked. If it is not recoverable or if a new service cannot possibly be selected, then the Exception is thrown.
Custom algorithms can be created by extending this class, and by supplying the new class as an argument to the setAlgorithm method of a ClusterableService (or by adding it to the service XML, if the service is externalized in jrun.xml or another XML file).

Author:

PS Neville

See Also:

RoundRobinAlgorithm, BuddyAlgorithm, StickyRoundRobinAlgorithm, Serialized Form

Field Summary

protected static java.util.Random

rand

Fields inherited from interface jrunx.cluster.ClusterConstants

AVAILABLE_SERVICES, CLUSTER_MANAGER_JNDI, DEFAULT_CLUSTER_DOMAIN, DEFAULT_ENABLED, JINI_CODE_BASE_JAR, PRIMARY_SERVICE, SECONDARY_SERVICE

Constructor Summary

ClusterAlgorithm()

Method Summary

static java.lang.Object	chooseRandom(java.util.ArrayList objects) Convenience method for randomly selecting an object from an array.
static java.lang.Object	chooseRandom(java.util.ArrayList objects, java.lang.Object exclude) Convenience method for randomly selecting an object from an array, and excluding one of the array's members.
static java.lang.Object	chooseStub(java.util.ArrayList objects, java.lang.String serverName) Convenience method for selecting an object from array based on the ServerName.
static ClusterableService	getPrefered()
Invocation	invokeService(Invocation inv)
protected Invocation	invokeService(Invocation inv, ClusterableService svc)
abstract ClusterableService	selectService(java.util.ArrayList services)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

rand

protected static java.util.Random rand

Constructor Detail

ClusterAlgorithm

public ClusterAlgorithm()

Method Detail

selectService

public abstract ClusterableService selectService(java.util.ArrayList services)
                                          throws java.rmi.RemoteException

invokeService

public Invocation invokeService(Invocation inv)
                         throws java.lang.Throwable

Throws:

java.rmi.RemoteException - propagated back to the client if there are no valid stubs

invokeService

protected Invocation invokeService(Invocation inv,
                                   ClusterableService svc)
                            throws java.lang.Throwable

chooseRandom

public static java.lang.Object chooseRandom(java.util.ArrayList objects)

Convenience method for randomly selecting an object from an array.

chooseStub

public static java.lang.Object chooseStub(java.util.ArrayList objects,
                                          java.lang.String serverName)

Convenience method for selecting an object from array based on the ServerName.

chooseRandom

public static java.lang.Object chooseRandom(java.util.ArrayList objects,
                                            java.lang.Object exclude)

Convenience method for randomly selecting an object from an array, and excluding one of the array's members.

getPrefered

public static ClusterableService getPrefered()