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Typically, the client will create the object reference once, save it in its own permanent storage area, and reactivate the servant for that object every time it comes up. If used with an Oracle Tuxedo CORBA Notification Service application, for example, these are callbacks that correspond to the concept of a persistent subscription; that is, the Notification Service remembers the callback reference and delivers events any time the client is up and declares that it is again ready to receive events. This allows notification service subscriptions to survive client failures or offline-time. (The corresponding POA policy values are PERSISTENT and SYSTEM_ID.)
interface Callbacks
{
exception ServantAlreadyActive{ };
exception ObjectAlreadyActive { };
exception NotInRequest{ };
// set up transient callback Object
// -- prepare POA, activate object, return objref
Object start_transient(
in PortableServer::Servant Servant,
in CORBA::RepositoryId rep_id)
raises (ServantAlreadyActive);// set up persistent/systemid callback Object
Object start_persistent_systemid(
in PortableServer::Servant servant,
in CORBA::Repository rep_id,
out string stroid)
raises (ServantAlreadyActive);// set up persistent/userid callback Object
Object start_persistent_userid(
in PortableServer::Servant servant,
in CORBA::RepositoryId rep_id,
in string stroid)
raises (ServantAlreadyActive, ObjectAlreadyActive);// get oid string for the current request
string get_string_oid() raises (NotInRequest);
};
}
#endif /* _BEA_WRAPPER _IDL_ */Listing 11‑4 C++ Declarations (in beawrapper.h)The BEAWrapper::Callbacks class has already be instantiated with an ORB pointer. Only one instance of this class can be used in a process. Users who need additional flexibility should use the POA directly.The repository id of the interface.The servant is already being used for a callback. A servant can be used only for a callback with a single ObjectId. To receive callbacks on objects containing different ObjectIds, you must create different servants and activate them separately. The same servant can be reused only if a stop_object operation tells the system to stop using the servant for its original ObjectId.
in PortableServer::Servant servant,
in CORBA::RepositoryId rep_id,
out string stroid)
raises ( ServantAlreadyActive );CORBA::Object_ptr start_persistent_systemid(
PortableServer::Servant servant,
const char* rep_id,
char*& stroid);
This argument is set by the system and is opaque to the user. The client will use it when it reactivates the object at a later time (using restart_persistent_systemid), most likely after the client process has terminated and restarted.The servant is already being used for a callback. A servant can be used only for a callback with a single ObjectId. To receive callbacks on objects containing different ObjectIds, you must create different servants and activate them separately. The same servant can be reused only if a stop operation tells the system to stop using the servant for its original ObjectId.
in PortableServer::Servant servant,
in CORBA::RepositoryId rep_id,
in string stroid)
raises (ServantAlreadyActive, ObjectAlreadyActive);CORBA::Object_ptr restart_persistent_systemid(
PortableServer::Servant servant,
const char* rep_id
const char* stroid);
The stringified version of the ObjectId provided by the user to be set in the object reference being created. It must have been returned from a previous call on start_persistent_systemid.The servant is already being used for a callback. A servant can be used only for a callback with a single ObjectId. To receive callbacks on objects containing different ObjectIds, you must create different servants and activate them separately. The same servant can be reused only if a stop_object operation tells the system to stop using the servant for its original ObjectId.The stringified ObjectId is already being used for a callback. A given ObjectId can have only one servant associated with it. If you wish to change to a different servant, you must first invoke stop_object with the servant currently in use.The repository ID was a NULL string or the servant was a NULL pointer or the ObjectId supplied was not previously assigned by the system.
portableServer::Servant a_servant,
in CORBA::RepositoryId rep_id,
in string stroid)
raises ( ServantAlreadyActive, ObjectAlreadyActive );The stringified version of an ObjectId provided by the user to be set in the object reference being created. The stroid holds application-specific data and is opaque to the ORB.The servant is already being used for a callback. A servant can be used only for a callback with a single ObjectId. To receive callbacks on objects containing different ObjectIds, you must create different servants and activate them separately. The same servant can be reused only if a stop_object operation tells the system to stop using the servant for its original ObjectId.The stringified ObjectId is already being used for a callback. A given ObjectId can have only one servant associated with it. If you wish to change to a different servant, you must first invoke stop_object with the servant currently in use.