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Debugging Batch Jobs

Contributed by Doug PenceFriday, 30 September 1994Last Updated Friday, 30 September 1994

Have you ever changed a batch program to run interactively just so you could use the debug feature on it? Have youever pondered buying a third-party debug tool just to find those errors that inevitably show up on job logs? Have you everstared at a program until your eyes glazed over trying to find the intermittent mystery error that keeps popping up whenthe third-shift operator runs the nightly batch run? If you an-swered yes to any of these questions, you should read thisarticle.

The system debugger that comes with your AS/400 may not have all the features of some of the third-party debuggers,but it has one great advantage the others cannot claim to have-it's free.

Most AS/400 programmers know the basics of starting debug, setting breakpoints, and displaying and changing programvariables. Let's skip the fundamentals and focus instead on debugging batch programs. Debugging batch jobs is not verydifferent from the debugging you're already familiar with.

Starting the Service Job

To run debug on a batch program, you need to use a feature called a service job. Before initiating the service job, youneed three components: the job name, the user, and the job number.

Finding the information is easy if the program happens to be at an error message or is already running (does the termlooping sound familiar?). You can use the Work with Active Jobs (WRKACTJOB) or Work with Submitted Jobs(WRKSBMJOB) command to find the job in question. When you select the Work with Job option, you will find the three

parameters you need displayed at the top of the screen as shown in 1.

Finding the information is easy if the program happens to be at an error message or is already running (does the termlooping sound familiar?). You can use the Work with Active Jobs (WRKACTJOB) or Work with Submitted Jobs(WRKSBMJOB) command to find the job in question. When you select the Work with Job option, you will find the threeparameters you need displayed at the top of the screen as shown in Figure 1.

If the job is already running, you need to put the job on hold using the WRKACTJOB or WRKSBMJOB panel.

On the other hand, if the job you want to debug is not already running, you need to go about it a little differently. You do

not want the job to begin running until you have initiated the service job. Place the job queue on hold using the Hold JobQueue (HLDJOBQ) command and then submit the job. Placing the job queue on hold does not stop existing programsfrom running, but it does keep new jobs in the queue from being initiated. Use the WRKSBMJOB command to get the jobidentification parameters, so you can start the service job.

By now, you should have written down the job name, user, and job number. You can run the Start Service Job(STRSRVJOB) command from any workstation. If you use F4 your screen will look like 2.

By now, you should have written down the job name, user, and job number. You can run the Start Service Job(STRSRVJOB) command from any workstation. If you use F4 your screen will look like Figure 2.

Starting Debug

Now that you have started the service job, you need to put the program into debug mode. You can use the Start Debug

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(STRDBG) command just as if you were putting an interactive program into debug mode. However, the system won't letyou add your breakpoints until the job begins.

Now it's time to release the job queue using the Release Job Queue (RLSJOBQ) command. If the job is already running,use the Release Job (RLSJOB) command. If the job has not yet started, a screen will be displayed letting you know thatthe serviced job is about to begin. You can expect a screen that looks something like 3.

Now it's time to release the job queue using the Release Job Queue (RLSJOBQ) command. If the job is already running,use the Release Job (RLSJOB) command. If the job has not yet started, a screen will be displayed letting you know thatthe serviced job is about to begin. You can expect a screen that looks something like Figure 3.

Defining Your Breakpoints

At this point, you must press F10 to get a command entry screen. You have put your program into debug, but you havenot told the system where you want it to break. Use the Add Breakpoint (ADDBKP) or Add Trace (ADDTRC) command todefine where you want your program to stop, just like you would if you were debugging an interactive job.

Perform the rest of the debug functions as if the program were running in an interactive job. That is all there is to it! Whenthe job completes, you receive another break message that tells you the job being serviced has ended. (Do not confusethis with ending the service job.)

Word of Caution

You will need to end both debug and the service job, or you may encounter problems later. Use the End Debug(ENDDBG) command followed by the End Service Job (ENDSRVJOB) command.

In Summary

Although it is a little clunky, debug on the AS/400 can be an extremely useful tool if you take the time to learn it. The CLProgrammer's Guide contains a useful chapter called "Testing Functions" that provides additional insights into debuggingboth interactive and batch jobs.

Doug Pence and Ron Hawkins have worked on IBM midrange systems for many years. Doug is the founder and Ron isthe research and development manager of Computer Processing Unlimited, Inc. in San Diego, California.

REFERENCE AS/400 CL Programmer's Guide (SC21-8077-2, CD-ROM QBKA7102).

Debugging Batch JobsFigure 1 The Work with Job Panel

Work with JobSystem: CPU

Job: ATBRPT User: QPGMR Number: 541492

Select one of the following:

1. Display job status attributes2. Display job definition attributes3. Display job run attributes, if active4. Work with spooled files

10. Display job log, if active or on job queue11. Display call stack, if active12. Work with locks, if active

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13. Display library list, if active14. Display open files, if active15. Display file overrides, if active16. Display commitment control status, if active

More...Selection or command===>

F3=Exit F4=Prompt F9=Retrieve F12=Cancel

Debugging Batch JobsFigure 2 Start Service Job Prompt

Start Service Job (STRSRVJOB)Type choices, press Enter.Job name . . . . . . . . . . . . JOB atbrpt

User . . . . . . . . . . . . . qpgmrNumber . . . . . . . . . . . . 541492

BottomF3=Exit F4=Prompt F5=Refresh F10=Additional parameters F12=CancelF13=How to use this display F24=More keys

Debugging Batch JobsFigure 3 The Released Serviced Job Screen

Start Serviced JobSystem: CPU

Job: ATBRPT User: QPGMR Number: 541492

The serviced job has been released from the job queue. Press Enter tostart the job or F10 to enter debug commands for that job.

Press Enter to continue.

F10=Command entry(C) COPYRIGHT IBM CORP. 1980, 1993.

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