14. Service Programs – ILE RPG in Easy Bytes

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ILE RPG in Easy Bytes

In Unit 14 you learn about service programs—what they are, how to create and maintain them, and when to use them. The unit also presents the concept of service program signatures and how to control them using binder language. In addition, it explains ILE activation groups, and how the various activation group options affect the resources an application uses.

This course includes hands-on lab exercises to help you understand the concepts behind service programs, binder language, and activation groups.

This course is a unit of the ILE RPG in Easy Bytes  series, a complete introductory ILE RPG programming self-guided tutorial.

 

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Service Programs

Creating Service Programs

Under this technique, a program includes a main procedure and optional subprocedures; all code for the program is physically copied into the program during the binding process. The resulting program (*Pgm object) is a single entry point program. The entry module contains the main procedure, which is the first user-written code that is executed when the program is called.
Using Service Programs

But the calling program does not call the service program itself. Because a service program lacks a main procedure, you cannot call it. Instead, the caller invokes an individual procedure in a service program by using the same syntax that it would use if the procedure were bound to it by copy:
Maintaining Service Programs

Instead of recreating the entire service program, though, you can use the UPDSRVPGM (Update Service Program) command to complete an abbreviated binding step. The UPDSRVPGM command lets you list just the module (or modules) that you want to remove from the original service program, replacing its code with the new version that now resides in the newly recompiled module. The UPDSRVPGM command performs the same functions as the CRTSRVPGM command, except that it replaces only the changed modules (i.
Exporting Data Items

In a modular programming environment, you can also use Export to define a variable or a data structure whose contents are available across modules. If a data item is used across several modules, you must define it within each relevant module. But only one module actually allocates storage for that data item.

Activation Groups

Understanding Activation Groups

The resources include the storage a program uses, certain error-handling routines, and temporary data management resources. Each job has its own activation groups, separate from other jobs. Within a job, a program can run in its own activation group, independent of other programs in the same job.
Activation Groups and File Overrides

Sometimes you need to make minor changes in how a program functions without recompiling the program. Maybe it’s necessary for a program to redirect a file declaration to process a file in a specific library, a file of another name, or a specific file member. Or perhaps the program must change some other attribute of a file.

Lab Exercise

Lab Exercise: Service Program

This lab teaches you how to create/update an ILE service program and use it with IBM i client programs; use a binding directory and binder language.