Package de.aristaflow.adept2.core.registry.cluster

Class ServiceStateTracker

java.lang.Object

de.aristaflow.adept2.core.registry.cluster.ServiceStateTracker

public final class ServiceStateTracker
extends Object

This class resembles the service state tracking of ClientService. It also tracks the availability of the platform by polling the cluster node state. Both issues are separately implemented.

The lifecycle of ClientService is coupled to the platform running on a cluster node. This platform may be restarted and may change between client and server role. However, service state listeners registered at the ClientService may have a different lifecycle and keep on running while the platform restarts. When restarting the platform and thus the ClientService the listeners will get lost and they will no longer receive notifications about a service. Additionally, they will not get notified about the restart of the ClientService where they would need to re-register.

This class solves this issue by being coupled to the lifecycle of ClusterNode. Additionally, listeners do not register with a service object (which is also coupled to the lifecycle of the platform and not of the one of a cluster node) but with the URI[] of a service. This is usually the global service URI which is resolved transparently considering all cluster nodes. Therefore the service may change its providing cluster node without the service state listener needing to change.

The availability of the platform will be tracked by a separate thread polling the cluster node state for changes. As soon as a changes occurs, it submits a runnable for notifying the registered listeners and immediately polls for a cluster node change again. Since this has to be outside of the platform lifecycle, the thread keeps on running while the cluster node exists. It stops as soon as the cluster node has terminated. The code bootstrapping the cluster node should also join() this thread. While the service state tracker may ignore the platform being unavailable, platform state listeners will be notified about every relevant change of the cluster node state. This may lead to consecutive notifications of the platform being unavailable (but the cluster node changing states while preparing the platform restart).

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
protected class	ServiceStateTracker.PlatformAvailabilityNotifier	A callable retrieving all listeners registered for platform state and submitting the corresponding notifications about the (un-)availability of the platform.
protected class	ServiceStateTracker.PlatformAvailabilityTracker	A thread tracking the availability of the platform.
static interface	ServiceStateTracker.PlatformStateListener	Listener for events that the availability of the platform within the cluster node has changed.
class	ServiceStateTracker.ServiceAvailabilityTracker	A tracker for the availability of a specific ADEPT2Service identified by its URI[].

Field Summary

Fields

Modifier and Type	Field	Description
protected Map<ArrayKey<URI>,ServiceStateTracker.ServiceAvailabilityTracker>	availTracker	The listeners registered for the availability of an ADEPT2Service and the corresponding service availability tracker.
protected ClusterNodeState	cns	The cluster node state for the platform availability tracker.
protected Logger	logger	The logger for problems occurring with the asynchronous notifications.
protected LimitedPipelineExecutor<Object>	platformAvailabilityNotifier	The executor for notifying the registered platform state listeners.
protected Thread	platformAvailabilityTracker	The thread tracking the availability of the platform by polling the cluster node state.
protected AbstractAuthenticatedService	platformService	The service used in the injected part of the cluster node/ClusterService.
protected long	pollRate	The rate in milliseconds at which to poll the availability of services serviceAvailibilityChecker.
protected int	poolSize	The amount of threads used for the serviceAvailibilityChecker.
protected Collection<ServiceStateTracker.PlatformStateListener>	psListeners	The listeners registered for changes in the platform availability.
protected HashSet<Status>	relevantStatuses	The statuses which are relevant for the (un-)availability of the platform.
protected ServiceAccess	servAccess	The access for services within the platform used to retrieve the polled services.
protected ScheduledExecutorService	serviceAvailibilityChecker	The thread pool for checking the availability of services and notifying changes to the registered listeners.

Constructor Summary

Constructors

Constructor	Description
ServiceStateTracker(int servAvailPoolSize, long servAvailPollRate, ClusterNodeState cns)	Creates a new service state tracker for a cluster node.

Method Summary

Modifier and Type	Method	Description
boolean	addPlatformStateListener(ServiceStateTracker.PlatformStateListener psl)	Registers the designated listener for changes in the availability of the platform.
boolean	addServiceStateListener(URI[] service, Class<? extends ADEPT2Service> servClass, ClientService.ServiceStateListener listener)	This is similar to ClientService.addServiceStateListener(ADEPT2Service, ServiceStateListener) except that it uses the URI[] of the service and the service class instead of the service instance.
void	join()	Joins the thread tracking the platform availability.
void	removePlatformStateListener(ServiceStateTracker.PlatformStateListener psl)	Removes the designated listener from changes in the availability of the platform.
void	removeServiceStateListener(URI[] service, ClientService.ServiceStateListener listener)	This is similar to ClientService.removeServiceStateListener(ADEPT2Service, ServiceStateListener) except that it uses the URI[] of the service instead of the service instance.
void	shutdown()	Signals the shutting down of the platform of the cluster node.
void	start(AbstractAuthenticatedService pService, ServiceAccess sAccess)	Starts this service state tracker each time the platform becomes available (again).

Methods inherited from class java.lang.Object

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

Field Detail

logger

protected final Logger logger

The logger for problems occurring with the asynchronous notifications.

poolSize

protected final int poolSize

The amount of threads used for the serviceAvailibilityChecker.

pollRate

protected final long pollRate

The rate in milliseconds at which to poll the availability of services serviceAvailibilityChecker.

availTracker

protected final Map<ArrayKey<URI>,ServiceStateTracker.ServiceAvailabilityTracker> availTracker

The listeners registered for the availability of an ADEPT2Service and the corresponding service availability tracker.

platformService

protected AbstractAuthenticatedService platformService

The service used in the injected part of the cluster node/ClusterService. This is used to track the state of the platform within the cluster node.

servAccess

protected ServiceAccess servAccess

The access for services within the platform used to retrieve the polled services.

serviceAvailibilityChecker

protected volatile ScheduledExecutorService serviceAvailibilityChecker

The thread pool for checking the availability of services and notifying changes to the registered listeners.

cns

protected final ClusterNodeState cns

The cluster node state for the platform availability tracker.

relevantStatuses

protected final HashSet<Status> relevantStatuses

The statuses which are relevant for the (un-)availability of the platform. Some intermediate statuses are not relevant.

psListeners

protected final Collection<ServiceStateTracker.PlatformStateListener> psListeners

The listeners registered for changes in the platform availability.

platformAvailabilityNotifier

protected final LimitedPipelineExecutor<Object> platformAvailabilityNotifier

The executor for notifying the registered platform state listeners. This is a pipeline executor to avoid later state notifications to overtake older state notifications.

platformAvailabilityTracker

protected final Thread platformAvailabilityTracker

The thread tracking the availability of the platform by polling the cluster node state.

Constructor Detail

ServiceStateTracker

public ServiceStateTracker(int servAvailPoolSize,
                           long servAvailPollRate,
                           ClusterNodeState cns)

Creates a new service state tracker for a cluster node.

Parameters:

servAvailPoolSize - The amount of threads used for the serviceAvailibilityChecker and the #platformAvailabilityNotifier.

servAvailPollRate - The rate in milliseconds at which to poll the availability of services serviceAvailibilityChecker.

cns - The cluster node state for the platform availability tracker.

Method Detail

start

public void start(AbstractAuthenticatedService pService,
                  ServiceAccess sAccess)

Starts this service state tracker each time the platform becomes available (again).

Parameters:

pService - The service used in the injected part of the cluster node/ClusterService. This is used to track the state of the platform within the cluster node.

sAccess - The access for services within the platform used to retrieve the polled services.

shutdown

public void shutdown()

Signals the shutting down of the platform of the cluster node. This removes access to the platform and terminates the executor service.

addServiceStateListener

public boolean addServiceStateListener(URI[] service,
                                       Class<? extends ADEPT2Service> servClass,
                                       ClientService.ServiceStateListener listener)

This is similar to ClientService.addServiceStateListener(ADEPT2Service, ServiceStateListener) except that it uses the URI[] of the service and the service class instead of the service instance. This is due to the service instance to be subject of change in case the platform within the cluster node changes.

Parameters:

service - The URI[] of the service to poll.

servClass - The class of the service to poll.

listener - The listener which to notify in case of service availability changes.

Returns:

Whether the designated service is currently available.

removeServiceStateListener

public void removeServiceStateListener(URI[] service,
                                       ClientService.ServiceStateListener listener)

This is similar to ClientService.removeServiceStateListener(ADEPT2Service, ServiceStateListener) except that it uses the URI[] of the service instead of the service instance.

Parameters:

service - The URI[] of the service which to no longer poll.

listener - The listener which to no longer notify in case of service availability changes.

addPlatformStateListener

public boolean addPlatformStateListener(ServiceStateTracker.PlatformStateListener psl)

Registers the designated listener for changes in the availability of the platform.

Parameters:

psl - The listener notified of changes in the availability of the platform.

Returns:

Whether the platform is currently available.

removePlatformStateListener

public void removePlatformStateListener(ServiceStateTracker.PlatformStateListener psl)

Removes the designated listener from changes in the availability of the platform.

Parameters:

psl - The listener which no longer to notify of changes in the availability of the platform.

join

public void join()
          throws InterruptedException

Joins the thread tracking the platform availability. The shutdown procedure should call this to prevent the platform availability tracker from surviving the final termination.

Throws:

InterruptedException - If the current thread is interrupted while waiting for the platform availability tracker, an InterruptedException will be thrown and the thread will not be joined.