Program Flow in RPG Modules: Cycle Versus Linear

The ILE RPG compiler supplies part of the logic for an RPG module. Depending on the type of module you choose, this supplied logic will control a large or small part of the control flow of your module. By default, an RPG module will include the full RPG Cycle, which begins with the *INIT phase and ends with the *TERM phase. The other two types of RPG modules do not include the full RPG Cycle; the only remnant of the RPG cycle is the module initialization, which is similar to the *INIT phase. The ILE RPG compiler supplies additional implicit logic that is separate from the RPG cycle; for example, the implicit opening and closing of local files in subprocedures.

All ILE RPG modules can have one or more procedures.

The three types of RPG modules are distinguished by the nature of the main procedure in the module.

A program or a service program can consist of multiple modules, each of which can have an RPG main procedure. If an RPG module is selected to be the program-entry module of a program, then you call the main procedure using a program call. If an RPG module is not the program-entry module of a program, or if it is a module in a service program, then you call its main procedure using a bound call. Calling a main procedure through a bound call is only available for cycle-main procedures; if a module contains a linear-main procedure and that module is not selected to be a program-entry module, than that procedure cannot be called.

A module with a cycle-main procedure

The module contains a cycle-main procedure and zero or more subprocedures. The cycle-main procedure includes the logic for the full RPG cycle. A cycle-main procedure can be called through a bound call, or through a program call. See Cycle Module and Program Cycle for more information.

A module with a linear-main procedure

The module contains a linear-main procedure and zero or more ordinary subprocedures. The linear-main procedure is identified by the MAIN keyword on the Control specification. The main procedure itself is coded as a subprocedure (with Procedure specifications). The linear-main procedure can only be called through a program call; it cannot be called using a bound call.

Note:

Other than the way it is called, the linear-main procedure is considered to be a subprocedure.

The module does not include the logic for the RPG cycle. See Linear Main Module for more information.

A module with no main procedure

The NOMAIN keyword on the Control specification indicates that there is no main procedure in the module. The module contains only subprocedures. The module does not include the logic for the RPG cycle.

This type of module cannot be the program-entry module of a program, since it has no main procedure.

See NOMAIN Module for more information.

Table 21. Summary of RPG module types
Module Type	Keyword	Cycle Features Allowed	Main Procedure	Initialization of global variables, opening of files, and UDS data areas	Implicit closing of global files and unlocking of data areas
Cycle-main		Yes	Implicitly defined in the main source section	When the first procedure in the module is called after the activation group is created. When the main procedure is called, if the main procedure previously ended with LR on, or ended abnormally.	When the main procedure ends with LR on, or ends abnormally.
Linear-main	MAIN	No	Explicitly defined with the MAIN keyword and Procedure specifications	When the main procedure is first called after the activation group is created, or if somehow a sub-procedure is called first.	Never
No main	NOMAIN	No	None, indicated by the presence of the NOMAIN keyword	When the first procedure in the module is called after the activation group is created	Never

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