02
Sat, Nov
2 New Articles

Practical RPG: Building Monitors with EOFDLY

RPG
Typography
  • Smaller Small Medium Big Bigger
  • Default Helvetica Segoe Georgia Times

 

Here's an alternative to data queues that works especially well when your primary input is a database file.

 

I've written two articles on how to use data queues. Data queues are especially practical when you're sending many messages with different layouts between multiple clients and servers. They're easy to create and don't require much in the way of initial design. Simply create the data queue and away you go!

 

The problem is that you do need extra objectstypically, externally described data structuresto define the layout of the different messages. It's not really a big deal with a complex architecture, but when you need a very directed type of communication, the data queue can be overkill. And that's when you can take advantage of a good old DB2 file.

 

The Simple Solution

 

Database tables make the most sense when you have a single-target fire-and-forget application. These usually appear in an inter-platform environment, where an event on one platform needs to be mirrored on another platform. This could be a high availability scenario or a migration environment where legacy events need to be posted to the new business solution (or vice versa). Let's take the simple case of a master file change (probably the best use of this design).

 

090314PluataImage1

Figure 1: Here's a simple master file synchronization application.

 

Whenever you have two different systems that need to share the same master data, you have to have some sort of synchronization process. In the old days, that might be done through nightly batch jobs, which simply shipped master files across the network. But in today's world, you often need a much more agile approach in which changes on one machine are mirrored almost automatically on the other machine. Figure 1 shows the simple outline of just such a business flow between a new system and the legacy system that it is communicating with. The new system is considered to be the system of record, meaning that all master file changes are done in the new system. Typically, in this environment, maintenance is disabled on the legacy system and the only way to get changes into the legacy database is by maintaining the corresponding data on the new system. With that methodology, changes clearly have to be transmitted to the legacy system immediately. In that case, the flow is simple: maintenance to the new database table is detected by the database monitor, which in turn uses some sort of interface (for example purposes, I chose a JDBC interface) to write a record to an interface file on the legacy system. In turn, a monitor on the legacy system senses the new record in the interface file and updates the appropriate legacy table. Each file has a different layout, with the interface file being the only table that the two systems have to agree upon. That file contains only those fields from the new system that are pertinent to the legacy system, and it's the only object for which changes need to be coordinated between the two systems. That's why I like using an interface file when the flow between the two processes is narrowly defined.

 

Where Does EOFDLY Come In?

 

This article, though, is not just about writing an interface; it's supposed to be about the EOFDLY keyword. Why would we use EOFDLY? Well, here's the main routine for a typical monitor program:

 

      dou %shtdn();

       read INTERFACE;

       if %eof(INTERFACE);

         DoDelay();

         iter;

       endif;

       Process();

      enddo;

 

Very simple and to the point. The primary loop is conditioned by the %shtdn BIF, which returns true when either the job or the subsystem is terminating. Using this technique, you can end the job or the subsystem using OPTION(*CNTRLD) and the monitor can end gracefully, performing any cleanup that might be necessary. This is a good habit to get into with monitor programs. This main routine calls two subprocedures: Process and DoDelay. Process is the part that edits the record and, if the data is valid, maintains the master file (you'll see later that this procedure stays constant regardless of whether we use EOFDLY or not). The piece that interests us here is the DoDelay procedure. I'm not going to go into detail on the routine; you've probably programmed these before. You can call a CL program to do a DLYJOB, or you can use the C libraries to call the sleep() function. Pick your favorite technique to delay the program for a few seconds (or minutes, depending on the application) and then try again. But here's the annoying piece: how do you debug this from the command line? Usually, you'd write a record to your interface and then call the program in debug mode and step through it. That's all fine and good up until the time that you finish processing. Then your program goes into a loop until you use System Request option 2 to cancel the program. Not my favorite technique since it doesn't do any cleanup.

 

Enter EOFDLY. It really simplifies the code. With EOFDLY, your program looks like this:

 

      dou %eof(INTERFACE);

       read INTERFACE;

       if not %eof(INTERFACE);

        Process();

       endif;

      enddo;

 

Notice that I don't use %shtdn. There's a reason for this: with EOFDLY, the operating system does not return control to your program until the RPG runtime senses a termination condition. Instead, when the data management routine senses EOF, it automatically delays the program for however long you indicated on the EOFDLY and then attempts another read. It's that simple. If you get an EOF, you know the job is shutting down, so you end the mainline routine and call your cleanup. So all you do is execute an OVRDBF file with an EOFDLY:

 

     OVRDBF     FILE(INTERFACE) EOFDLY(30)


So now, whenever there are no records in the file, the system waits 30 seconds and tries again. But how does this make it easier to debug? To understand that, look at the routine. What happens if you don't specify EOFDLY? As soon as the program sees EOF, it exits the loop. So to test, all you have to do is write one or more records to the interface file and call the RPG without doing the override. The program will process each record, and then when there are no more, it will end gracefully. I've found this simple technique to be really helpful in testing, especially for unit test scenarios: create a test program that writes specific record to the interface file and then call that program followed but the interface monitor to make sure that the records are processed correctly. It's a fantastic technique.

 

So that's EOFDLY in a nutshell. Like any technique, it's not universally applicable, but where it does make sense it's hard to beat.

 

Joe Pluta

Joe Pluta is the founder and chief architect of Pluta Brothers Design, Inc. He has been extending the IBM midrange since the days of the IBM System/3. Joe uses WebSphere extensively, especially as the base for PSC/400, the only product that can move your legacy systems to the Web using simple green-screen commands. He has written several books, including Developing Web 2.0 Applications with EGL for IBM i, E-Deployment: The Fastest Path to the Web, Eclipse: Step by Step, and WDSC: Step by Step. Joe performs onsite mentoring and speaks at user groups around the country. You can reach him at This email address is being protected from spambots. You need JavaScript enabled to view it..


MC Press books written by Joe Pluta available now on the MC Press Bookstore.

Developing Web 2.0 Applications with EGL for IBM i Developing Web 2.0 Applications with EGL for IBM i
Joe Pluta introduces you to EGL Rich UI and IBM’s Rational Developer for the IBM i platform.
List Price $39.95

Now On Sale

WDSC: Step by Step WDSC: Step by Step
Discover incredibly powerful WDSC with this easy-to-understand yet thorough introduction.
List Price $74.95

Now On Sale

Eclipse: Step by Step Eclipse: Step by Step
Quickly get up to speed and productivity using Eclipse.
List Price $59.00

Now On Sale

BLOG COMMENTS POWERED BY DISQUS

LATEST COMMENTS

Support MC Press Online

$

Book Reviews

Resource Center

  • SB Profound WC 5536 Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application. You can find Part 1 here. In Part 2 of our free Node.js Webinar Series, Brian May teaches you the different tooling options available for writing code, debugging, and using Git for version control. Brian will briefly discuss the different tools available, and demonstrate his preferred setup for Node development on IBM i or any platform. Attend this webinar to learn:

  • SB Profound WP 5539More than ever, there is a demand for IT to deliver innovation. Your IBM i has been an essential part of your business operations for years. However, your organization may struggle to maintain the current system and implement new projects. The thousands of customers we've worked with and surveyed state that expectations regarding the digital footprint and vision of the company are not aligned with the current IT environment.

  • SB HelpSystems ROBOT Generic IBM announced the E1080 servers using the latest Power10 processor in September 2021. The most powerful processor from IBM to date, Power10 is designed to handle the demands of doing business in today’s high-tech atmosphere, including running cloud applications, supporting big data, and managing AI workloads. But what does Power10 mean for your data center? In this recorded webinar, IBMers Dan Sundt and Dylan Boday join IBM Power Champion Tom Huntington for a discussion on why Power10 technology is the right strategic investment if you run IBM i, AIX, or Linux. In this action-packed hour, Tom will share trends from the IBM i and AIX user communities while Dan and Dylan dive into the tech specs for key hardware, including:

  • Magic MarkTRY the one package that solves all your document design and printing challenges on all your platforms. Produce bar code labels, electronic forms, ad hoc reports, and RFID tags – without programming! MarkMagic is the only document design and print solution that combines report writing, WYSIWYG label and forms design, and conditional printing in one integrated product. Make sure your data survives when catastrophe hits. Request your trial now!  Request Now.

  • SB HelpSystems ROBOT GenericForms of ransomware has been around for over 30 years, and with more and more organizations suffering attacks each year, it continues to endure. What has made ransomware such a durable threat and what is the best way to combat it? In order to prevent ransomware, organizations must first understand how it works.

  • SB HelpSystems ROBOT GenericIT security is a top priority for businesses around the world, but most IBM i pros don’t know where to begin—and most cybersecurity experts don’t know IBM i. In this session, Robin Tatam explores the business impact of lax IBM i security, the top vulnerabilities putting IBM i at risk, and the steps you can take to protect your organization. If you’re looking to avoid unexpected downtime or corrupted data, you don’t want to miss this session.

  • SB HelpSystems ROBOT GenericCan you trust all of your users all of the time? A typical end user receives 16 malicious emails each month, but only 17 percent of these phishing campaigns are reported to IT. Once an attack is underway, most organizations won’t discover the breach until six months later. A staggering amount of damage can occur in that time. Despite these risks, 93 percent of organizations are leaving their IBM i systems vulnerable to cybercrime. In this on-demand webinar, IBM i security experts Robin Tatam and Sandi Moore will reveal:

  • FORTRA Disaster protection is vital to every business. Yet, it often consists of patched together procedures that are prone to error. From automatic backups to data encryption to media management, Robot automates the routine (yet often complex) tasks of iSeries backup and recovery, saving you time and money and making the process safer and more reliable. Automate your backups with the Robot Backup and Recovery Solution. Key features include:

  • FORTRAManaging messages on your IBM i can be more than a full-time job if you have to do it manually. Messages need a response and resources must be monitored—often over multiple systems and across platforms. How can you be sure you won’t miss important system events? Automate your message center with the Robot Message Management Solution. Key features include:

  • FORTRAThe thought of printing, distributing, and storing iSeries reports manually may reduce you to tears. Paper and labor costs associated with report generation can spiral out of control. Mountains of paper threaten to swamp your files. Robot automates report bursting, distribution, bundling, and archiving, and offers secure, selective online report viewing. Manage your reports with the Robot Report Management Solution. Key features include:

  • FORTRAFor over 30 years, Robot has been a leader in systems management for IBM i. With batch job creation and scheduling at its core, the Robot Job Scheduling Solution reduces the opportunity for human error and helps you maintain service levels, automating even the biggest, most complex runbooks. Manage your job schedule with the Robot Job Scheduling Solution. Key features include:

  • LANSA Business users want new applications now. Market and regulatory pressures require faster application updates and delivery into production. Your IBM i developers may be approaching retirement, and you see no sure way to fill their positions with experienced developers. In addition, you may be caught between maintaining your existing applications and the uncertainty of moving to something new.

  • LANSAWhen it comes to creating your business applications, there are hundreds of coding platforms and programming languages to choose from. These options range from very complex traditional programming languages to Low-Code platforms where sometimes no traditional coding experience is needed. Download our whitepaper, The Power of Writing Code in a Low-Code Solution, and:

  • LANSASupply Chain is becoming increasingly complex and unpredictable. From raw materials for manufacturing to food supply chains, the journey from source to production to delivery to consumers is marred with inefficiencies, manual processes, shortages, recalls, counterfeits, and scandals. In this webinar, we discuss how:

  • The MC Resource Centers bring you the widest selection of white papers, trial software, and on-demand webcasts for you to choose from. >> Review the list of White Papers, Trial Software or On-Demand Webcast at the MC Press Resource Center. >> Add the items to yru Cart and complet he checkout process and submit

  • Profound Logic Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application.

  • SB Profound WC 5536Join us for this hour-long webcast that will explore:

  • Fortra IT managers hoping to find new IBM i talent are discovering that the pool of experienced RPG programmers and operators or administrators with intimate knowledge of the operating system and the applications that run on it is small. This begs the question: How will you manage the platform that supports such a big part of your business? This guide offers strategies and software suggestions to help you plan IT staffing and resources and smooth the transition after your AS/400 talent retires. Read on to learn: