Service Activator Toolkit

Understanding Events

To be able to successfully use SAT's Managed Service and Managed Service Factory support, it is helpful to understand how events are handled. The following diagrams are intended to help understand where events come from and how they are dispatched to the advisor for handling. As you read this section, refer to both the discussion and the implementation of the examples since this will aid your understanding.

There are two types of events to consider, synchronous and asynchronous. events.

Synchronous Events: These events mostly originate from Configuration Admin in response to changes in the configurations.

Updated Configuration: When a configuration change occurs it must be decided whether the configuration is new, or an update to an existing configuration.

If the configuration is new an instance of IBundleActivationManager is created and started.

If the configuration is not new a comparison of the old and new properties must be performed to see if they've changed; if the properties have not changed the update is ignored.

If the configuration is new, or if the properties have changed, the method createImportedServiceFilters is called on the advisor. The advisor's implementation of the createImportedServiceFilters method calls the manager's addImportServiceFilter method that causes the manager's imported services to be released and/or acquired to match the specified LDAP filters.

As services are acquired asynchronous Service Acquired Events arrive. If the object created by the advisor for the configuration is not new then the advisor's update method is called to ensure that the object is updated appropriately with properties that do not affect the manager's imported service filters.

Deleted Configuration: When a ManagedServiceFactory's configuration is deleted the IBundleActivationManager associated with the configuration is stopped, causing the manager's imported services to be released. As the manager's imported services are released asynchronous Service Released Events arrive.

Synchronous event also arrive from the OSGi framework when the bundle that registered the ManagedService or ManagedServiceFactory is stopped.

Stopped: When the bundle stops the IBundleActivationManager for each configuration is also stopped. When a manager stops its imported services are released. As services are released asynchronous Service Released Events arrive.

Asynchronous Events: These events originate from the OSGi framework as a result of services being registered with the framework and subsequently acquired by the manager, and unregistered with the framework and subsequently released by the manager. These events instruct SAT that it should create or destroy an object associated with a configuration.

Service Acquired Events: These events are ignored until the manager has acquired all its imported services. Once fully acquired the advisor's create method is called to create an object associated with the configuration. This object is returned and managed by SAT.
Service Released Events: If fully acquired the releasing of the first imported service causes the advisor's destroy method to be called and the object associated with the configuration destroyed. Subsequent events are ignored.

While the details of where events come from and how they are handled can be rather complicated studying the diagram and the example while implementing a Managed Service or Managed Service Factory is highly recommended.