IMS Callable Services

IMS Callable Services are services provided by IMS for use by IMS exit routines. These services provide clearly defined interfaces that allow exit routines to request various functions.

There are three types of IMS Callable Services: storage services, control block services, and automated operator interface (AOI) services.

Storage Services

Storage services support four functions:

• Get storage: Used to obtain user storage

• Free storage: Used to release user storage previously obtained by the GET storage service

• Load module: Used to load a module

• Delete module: Used to delete a module previously obtained by the LOAD storage service

Control Block Services

Control block services support two functions:

• Find control block: Used to find a specific instance of a control block

• Scan control block: Used to scan control blocks of a certain type

Automated Operator Interface Services

AOI services support three functions:

• Insert message: Used to insert the first, or a subsequent, message segment into a message buffer

• Enqueue message: Used to insert the last or only message segment into the message buffer

• Cancel message: Used to cancel messages that have been inserted into the message buffer but not yet enqueued

Using Callable Services

To use a callable service, do the following:

1.	Bind your exit routine to the callable service interface module.
2.	Initialize callable services for your exit routine each time your exit routine gets control.
3.	Initialize the callable services parameter list.
4.	Initialize the function-specific parameter list.
5.	Invoke the callable service.

Repeat steps 3 through 5 as many times as necessary while your exit routine has control. Not all exit routines perform all five of the preceding steps.