Use multiple service components

We can install more than one component for a service. This allows components to provide only partial implementations of the service, and to rely on other components to provide the remaining functions.

Example of using multiple components

Suppose you create two a name services components called ABC_name_serv and XYZ_name_serv.

ABC_name_serv

This component supports inserting a name in, or deleting a name from, the service directory, but does not support looking up a queue name.

XYZ_name_serv

This component supports looking up a queue name, but does not support inserting a name in, or deleting a name from, the service directory.

Component ABC_name_serv holds a database of queue names, and uses two simple algorithms to either insert, or delete, a name from the service directory.

Component XYZ_name_serv uses a simple algorithm that returns a fixed queue manager name for any queue name with which it is invoked. It does not hold a database of queue names, and therefore does not support the insert and delete functions.

The components are installed on the same queue manager. The ServiceComponent stanzas are ordered so that component ABC_name_serv is invoked first. Any calls to insert or delete a queue in a component directory are handled by component ABC_name_serv ; it is the only one that implements these functions. However, a lookup call that component ABC_name_serv cannot resolve is passed on to the lookup-only component, XYZ_name_serv. This component supplies a queue manager name from its simple algorithm.

Omitting entry points when using multiple components

If you decide to use multiple components to provide a service, we can design a service component that does not implement certain functions. The installable services framework places no restrictions on which we can omit. However, for specific installable services, omission of one or more functions might be logically inconsistent with the purpose of the service.

Example of entry points used with multiple components

Table 1 shows an example of the installable name service for which the two components have been installed. Each supports a different set of functions associated with this particular installable service. For insert function, the ABC component entry-point is invoked first. Entry points that have not been defined to the service (using MQZEP ) are assumed to be NULL. An entry-point for initialization is provided in the table, but this is not required because initialization is carried out by the main entry-point of the component.

When the queue manager has to use an installable service, it uses the entry-points defined for that service (the columns in Table 1 ). Taking each component in turn, the queue manager determines the address of the routine that implements the required function. It then calls the routine, if it exists. If the operation is successful, any results and status information are used by the queue manager.

Function number	ABC name service component	XYZ name service component
MQZID_INIT_NAME (Initialize)	ABC_initialize()	XYZ_initialize()
MQZID_TERM_NAME (Terminate)	ABC_terminate()	XYZ_terminate()
MQZID_INSERT_NAME (Insert)	ABC_Insert()	NULL
MQZID_DELETE_NAME (Delete)	ABC_Delete()	NULL
MQZID_LOOKUP_NAME (Lookup)	NULL	XYZ_Lookup()

If the routine does not exist, the queue manager repeats this process for the next component in the list. In addition, if the routine does exist but returns a code indicating that it could not perform the operation, the attempt continues with the next available component. Routines in service components might return a code that indicates that no further attempts to perform the operation should be made.

Parent topic: Writing a service component