Understanding Events

To be able to successfully use the abstract classes ManagedServiceFactoryBundleActivator and BaseManagedServiceFactoryAdvisor it is helpful to understand how the various events are handled. The flow diagram below should help understand where events come from and how they are handled. As you read this section, refer to both the dialog and the implementation of the example since this will aid your understanding.

Understanding Events

There are two types of events to consider:

Synchronous Events: These events mostly originate from Configuration Admin and instruct the factory that a configuration has been updated and deleted.
- Updated Configuration: When a configuration is updated the factory decides whether or not the configuration is new. If the configuration is new the factory creates and starts an instance of IBundleActivationManager. If the configuration is not new the factory compares the updated properties with the ones it currently has for the configuration 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 advisor's createImportedServiceFilters method is called. 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 released asynchronous Service Released Events arrive. As services are acquired asynchronous Service Acquired Events arrive. See below for details of asynchronous events. 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 configuration is deleted the factory stops the IBundleActivationManager associated with the configuration, causing the manager's imported services to be released. As the manager's imported services are released asynchronous Service Released Events arrive. See below for details of asynchronous events.
Synchronous event also arrive from the OSGi framework when the factory bundle is stopped.
- Stopped: When the factory bundle stops it stops the IBundleActivationManager for each configuration. When a manager stops its imported services are released. As services are released asynchronous Service Released Events arrive. See below for details of asynchronous events.
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 the factory 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 the factory.
- 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 Factory is highly recommended.