ILE Programming › Service Program Design and Generation › Service Program Overview

Service Program Overview

Within the CA 2E product, external functions can be defined with an object attribute of either PGM or a MOD. When compiled, these functions become one of two i OS object types-respectively, a *PGM (executable program) or a *MODULE (non-executable module).

A *PGM object can be directly called, either from a command-line or from another program (assuming the correct parameters are passed). By contrast, a *MODULE object must first be 'bound' into an executable program.

Earlier releases of CA 2E provided the following ILE-specific functionality:

• An external function could be given an attribute of MOD (instead of PGM). This function would compile into a i OS *MODULE rather than a *PGM.
• All MOD functions are automatically added to the 2E model's default binding directory YBNDDIR during the compilation process.
• The default compilation command for ILE programs forces the compiler to search YBNDDIR for called bound modules.
• Calls to a MOD function would be generated (in RPG) as a CALLB (call-bound) rather than a CALL.

Note: Developers could then define certain external functions (typically ones that would never be called from a command line, such as SELRCD's) as modules. Any programs that called these functions (EDTFIL's, etc.) would include a copy of the module object. In ILE terms, this is known as bind-by-copy.

For example, the following diagram shows the use of three PGM functions calling two MOD functions and the resulting *PGM objects containing copies of the *MODULE objects:

This has a number of benefits:

• Fewer *PGM objects required at runtime can simplify application deployment.
• Calls to bound modules are typically quicker than calls to other programs, due to significantly reduced object pointer resolution overhead.

However, if a module is bound into a program and the code within the module function needs to be changed, the *MODULE must be recompiled and then any programs that bind that module must be changed to include the new copy of the module-typically this would be done by regenerating/recompiled the PGM function in a 2E model, although the i OS UPDPGM command can be run from outside the model environment.

Note: Although there are fewer *PGM objects, they are larger than if they did not contain a copy of the module.