Building the Safety Net: Global Message Monitoring and Exception Handling in CLLE

Have you…,

Ever faced a critical error in your IBM i system that halted your operations?

Then…,

Discover how global message monitoring in CLLE can keep your applications running smoothly.

Introduction

Exception handling is more than just technical – it’s about gracefully navigating unexpected situations. It is crucial to create user-friendly CLLE programs. In this blog, we discuss the fundamentals of global message monitoring, enabling you to create resilient and informative apps.

In CLLE (Control Language for AS/400), global monitors are common for robust error management. We’ll explore key points, followed by a sample program and its results.

Steps in Implementing a Global Monitor in CLLE for Message Handling:

1. Monitor Message Command

• Use a standardized template for your CLLE programs, including error handling and global message monitoring.
• To ensure consistent and reliable error management practices, include error-handling commands across all CLLE programs within your organization.
• Use the `MONMSG` (Monitor Message) command in CLLE to trap specific or generic messages that may occur during program execution.
• By placing the `MONMSG` command after the last declare statement in your program you can create a global monitor that captures unhandled messages.

1. Error Routine

• In your program, define an error routine that is triggered when an unexpected error occurs.
• Handle the captured messages appropriately within the error routine, such as sending diagnostic messages back to the calling program or taking necessary steps based on the error type.
• We can send the message in 2 ways:

1. Sending a User customized message to the calling program.
2. Receive an actual exception message and send it to the calling program.

3. Handling Unexpected Errors

• Ensure that your error routine can handle unexpected errors gracefully to prevent program crashes and provide meaningful feedback to users.
• Use the `SNDPGMMSG` (Send Program Message) command to send messages back to the calling program indicating abnormal program termination or diagnostic information.

4. Avoiding Infinite Loops

• Set flags or conditions in your error routine to prevent infinite loops in case of recurring errors.

5. Documentation and Comments

• It is important to document your code effectively, including comments that explain the purpose and functionality of your global monitor and error-handling functions.
• Ensure that IBM i developers can easily understand and maintain the error-handling logic within your CLLE programs.

Sample program

The following is a simple CLLE program that includes message monitoring at the program level.

Line 13 – 14: Global MONMSG to capture all the listed Message IDs.

Line 16 – 18: Main processing Body of the CL.

Line 23 – 37: Global monitoring error routine triggered while any unexpected errors occurred in the program.

Here we receive the type of error through RCVMSG (which will retrieve the message from the message queue).

RCVMSG usually consists of multiple parameters, and we used the 3 most important parms out of them.

MSGTYPE(*LAST) – The last message currently on the message queue or program queue is received.

MSG(&GLOBALMSG) – Contains the message when it is received by the program.

RMV(*NO) – The message is not removed from the message queue and Specifies whether the exception is to be handled. No – Not handled.

Line 26 – 29: Merges the system exception message with our custom message and sends it to the calling program.

Line 33 – 36: This is the logic to prevent infinite loops in case of recurring errors. ERRCNT (Line 23) will be increased by one value whenever the Global error handling routine has hit. It also helps to send a customized message to the calling program when the count value crosses 1.

Output:

1. We have a sample program that contains two numeric parameters. When I called it without parameters, I received the following error message.

2. When called with junk values.

3. CPYTOIMPF fails when called with the correct parameters. This is a generic error letting users know without throwing hard errors.

4. To test how ERRCNT avoids an infinite loop of recurring errors, I copied the CPYTOIMPF command into the error handling routine.

Conclusion

Exception handling and global message monitoring are core components of robust CLLE programs on IBM i systems. CLLE applications can be made more reliable, maintainable, and quality by proactively monitoring messages and implementing structured exception handling. By following the outlined steps and best practices, you can ensure that your programs handle errors gracefully and continue to operate smoothly in the face of unexpected challenges.

To further enhance the security and stability of your CLLE programs, consider leveraging IBM i Security Support services. Our expert team can:

• Conduct security audits and vulnerability assessments.
• Implement and manage security controls.
• Provide guidance on secure coding practices.
• Assist with incident response and recovery.

These strategies will not only improve application stability but also improve the user experience for both administrators and end users. Happy coding!