US.4. Introduction to the Helper Services

US.4.1. The Lookup Discovery Service

Under certain circumstances, a discovering entity may find it useful to allow a third party to perform the entity’s discovery duties. For example, an activatable entity that wishes to deactivate may wish to employ a separate helper service to perform discovery duties on the entity’s behalf. Such an entity may wish to deactivate for various reasons, one being to conserve computational resources. While the entity is deactivated, the helper service, running on the same or a separate host, would employ the discovery protocols to find lookup services in which the entity has expressed interest and would notify the entity when a previously unavailable lookup service becomes available. Such a helper service is referred to as a lookup discovery service.

The LookupDiscoveryService interface defines the lookup discovery helper service. Through that interface, other Jini services and clients may request that discovery processing be performed on their behalf.

US.4.2. The Lease Renewal Service

The lease renewal service—defined by the net.jini.lease.LeaseRenewalService interface—is a helper service that can be employed by both Jini clients and services to perform all lease renewal duties on their behalf. Services that wish to remain inactive until they are needed may find the lease renewal service quite useful. Such a service can request that the lease renewal service take on the responsibility of renewing the leases granted to the service, and then safely deactivate without risking the loss of access to the resources corresponding to the leases being renewed.

Entities that have continuous access to a network but that cannot be continuously connected to that network (for example, a cell phone), may also find this service useful. By allowing a lease renewal service (which can be continuously connected) to renew the leases on the resources acquired by the entity, the entity may remain disconnected until needed. This lease renewal service removes the need to perform the discovery and lookup process each time the entity reconnects to the network, potentially resulting in a significant increase in efficiency.

US.4.3. The Event Mailbox Service

The event mailbox service defined by the net.jini.event.EventMailbox interface is a helper service that can be employed by entities to store event notifications on their behalf. When an entity registers with the event mailbox service, that service will collect events intended for the registered entity until the entity initiates delivery of the events.

A service such as the event mailbox service can be particularly useful to entities that desire more control over the delivery of the events sent to them. Some entities operating in a distributed system may find it undesirable or inefficient to be contacted solely for the purpose of having an event delivered, preferring to defer the delivery to a time that is more convenient, as determined by the entity itself.

For example, an entity wishing to deactivate or detach from a network may wish to have its events stored until the entity is available to retrieve them. Additionally, some entities may wish to batch process event notifications for efficiency. In both scenarios, the entities described may find the event mailbox service useful in achieving their respective event delivery goals.