Changing a Module or Program - IBM - RPG

An ILE object may need to be changed for enhancements or for maintenance reasons. You can isolate what needs to be changed by using debugging information or the binder listing from the CRTPGM command. From this information you can determine what module needs to change, and often, what procedure or field needs to change.

In addition, you may want to change the optimization level or observability of a module or program. This often happens when you want to debug an program or module, or when you are ready to put a program into production. Such changes can be performed more quickly and use fewer system resources than re-creating the object in question.

Finally, you may want to reduce the program size once you have completed an application. ILE programs have additional data added to them which may make them larger than a similar OPM program.

Each of the above requires different data to make the change. The resources you need may not be available to you for an ILE program. The following sections tell you how to

  • Update a program
  • Change the optimization level
  • Change observability
  • Reduce the object size

Note: In the remainder of this section the term ’object’ will be used to refer to either an ILE module or ILE program.

Using the UPDPGM Command
In general, you can update a program by replacing modules as needed. For example, if you add a new procedure to a module, you recompile the module object, and then update the program. You do not have to re-create the program. This is helpful if you are supplying an application to other sites. You need only send the revised modules, and the receiving site can update the application using the UPDPGM or UPDSRVPGM command.

The UPDPGM command works with both program and module objects. The parameters on the command are very similar to those on the CRTPGM command. For example, to replace a module in a program, you would enter the module name for MODULE parameter and the library name. The UPDPGM command requires that the modules to be replaced be in the same libraries as when the program was created. You can specify that all modules are to be replaced, or some subset.

The UPDPGM command requires that the module object be present. Thus, it is easier to use the command when you have created the program using separate compile and bind steps. Since the module object already exists, you simply specify its name and library when issuing the command.

To update a program created by CRTBNDRPG command, you must ensure that the revised module is in the library QTEMP. This is because the temporary module used when the CRTBNDRPG command was issued, was created in QTEMP. Once the module is in QTEMP, you can issue the UPDPGM command to replace the module.

Changing the Optimization Level
Optimizing an object means looking at the compiled code, determining what can be done to make the run-time performance as fast as possible, and making the necessary changes. In general, the higher the optimizing request, the longer it takes to create an object. At run time the highly optimized program or service program should run faster than the corresponding nonoptimized program or service program.

However, at higher levels of optimization, the values of fields may not be accurate when displayed in a debug session, or after recovery from exception. In addition, optimized code may have altered breakpoints and step locations used by the source debugger, since the optimization changes may rearrange or eliminate some statements.

To ensure that the contents of a field reflect their most current value, especially after exception recovery, you can use the NOOPT keyword on the corresponding Definition specification. For more information, see “Optimization Considerations”.

To circumvent this problem while debugging, you can lower the optimization level of a module to display fields accurately as you debug a program, and then raise the level again afterwards to improve the program efficiency as you get the program ready for production.

To determine the current optimization level of a program object, use the DSPPGM command. Display 3 of this command indicates the current level. To change the optimization level of a program, use the CHGPGM command. On the Optimize program parameter you can specify one the following values: *FULL, *BASIC, *NONE. These are the same values which can be specified on the OPTIMIZE parameters of either create command. The program is automatically re-created when the command runs.

Similarly, to determine the current optimization level of a module, use the DSPMOD command. Display 1,of this command indicates the current level. To change the optimization level, use the CHGMOD command. You then need to re-create the program either using UPDPGM or CRTPGM.

Removing Observability
Observability involves the kinds of data that can be stored with an object, and that allow the object to be changed without recompiling the source. The addition of this data increases the size of the object. Consequently, you may want to remove the data in order to reduce object size. But once the data is removed, observability is also removed. You must recompile the source and recreate the program to replace the data. The types of data are:

Create Data
Represented by the *CRTDTA value. This data is necessary to translate the code to machine instructions. The object must have this data before you can change the optimization level.

Debug Data
Represented by the *DBGDTA value. This data is necessary to allow an object to be debugged.

Profiling Data
Represented by the *BLKORD and *PRCORD values. This data is necessary to allow the system to re-apply block order and procedure order profiling data.

Use the CHGPGM command or the CHGMOD command to remove some or all the data from a program or module respectively. Removing all observability reduces an object to its minimum size (without compression). It is not possible to change the object in any way unless you re-create it. Therefore, ensure that you have all source required to create the program or have a comparable program object with CRTDATA. To re-create it, you must have authorization to access the source code.

Reducing an Object’s Size
The create data (*CRTDTA) associated with an ILE program or module may make up more than half of the object’s size. By removing or compressing this data, you will reduce the secondary storage requirements for your programs significantly.

If you remove the data, ensure that you have all source required to create the program or have a comparable program object with CRTDATA. Otherwise you will not be able to change the object.

An alternative is to compress the object, using the Compress Object (CPROBJ) command. A compressed object takes up less system storage than an uncompressed one. If the compressed program is called, the part of the object containing the runnable code is automatically decompressed. You can also decompress a compressed object by using the Decompress Object (DCPOBJ) command.

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