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Service Program Overview

Chapter 8. Creating a Service Program

This chapter provides:

¹ An overview of the service program concept

¹ Strategies for creating service programs

¹ A brief description of the CRTSRVPGM command

¹ An example of a service program

Service Program Overview

A service program is a bound program (type *SRVPGM) consisting of a set of pro-

cedures that can be called by procedures in other bound programs.

Service programs are typically used for common functions that are frequently called

within an application and across applications. For example, the ILE compilers use

service programs to provide run-time services such as math functions and

input/output routines. Service programs enable reuse, simplify maintenance, and

reduce storage requirements.

A service program differs from a program in two ways:

¹ It does not contain a program entry procedure. This means that you cannot call

a service program using the CALL operation.

¹ A service program is bound into a program or other service programs using

binding by reference.

When you bind a service program to a program, the contents of the service

program are not copied into the bound program. Instead, linkage information of the

service program is bound into the program. This is called 'binding by reference' in

contrast to the static binding process used to bind modules into programs.

Because a service program is bound by reference to a program, you can call the

service program's exported procedures using bound procedure calls. The initial call

has a certain amount of overhead because the binding is not completed until the

service program is called. However, subsequent calls to any of its procedures are

faster than program calls.

The set of exports contained in a service program are the interface to the services

provided by it. You can use the Display Service Program (DSPSRVPGM) command

or the service program listing to see what variable and procedure names are avail-

able for use by the calling procedures. To see the exports associated with service

program PAYROLL, you would enter:

DSPSRVPGM PAYROLL DETAIL(*PROCEXP *DATAEXP)

1 2 ... 110 111 112 113 114 115 116 117 118 119 120 ... 488 489

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IBM AS/400 User Manual Page 115