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TechTip: WRKJVMJOB: Who's Been Running Java in My Shop?

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More and more Java is running under the covers on IBM i shops, and this command helps you see where.

 

Even as more and more shops embrace Java, they find that Java doesn't quite fit into the work management framework we've become familiar with on the IBM midrange platform. Specifically, WRKACTJOB just doesn't work the way we need it to. But as of version 6.1, we now have a new tool, WRKJVMJOB.

Java Is a Little Different

If you try to look at a Java job using the traditional WRKACTJOB tools, you won't see much. If you submit a job that calls Java (for example, by using the RUNJVA command), its job log will end with the call to the RUNJVA command and its call stack will be sitting on a call to the program QP0LLIB1, which is a service program that waits on a socket.

 

Socket? What's that all about? Well, what happened is that your program doesn't actually run the Java code. Instead, your job submits another job that actually runs the Java code. If you execute WRKUSRJOB, you can probably find it; the job will be of type BATCHI, and the function will begin with the characters JVM.

 

But even if you find the job, traditional i5/OS work management won't give you a lot of information. The job log will have a few messages about starting the JVM, and that's typically about it. The call stack will be similarly cryptic, with calls to PASE programs and lots of UNIX-y stuff like .so files.

Enter WRKJVMJOB

So, in V6.1, IBM introduced a set of tools that makes it easier for Java developers to monitor Java jobs. Foremost among these is the WRKJVMJOB command. Just hit WRKJVMJOB, and you'll see a list of all the JVM jobs running on your machine:

                               Work with JVM Jobs                      MYI 

                                                             02/05/12  11:42:24

 Active JVMs on system:   5                                                    

                                                                                

 Type options, press Enter.                                                    

   5=Work with   7=Display job log   8=Work with spooled files                 

   9=Display GC information          11=Display threads   12=Dump   13=Print   

 Opt  Job Name    User        Number  Function          Status                 

  _   QSRVMON     QSYS        343115  JVM-ServiceMon     THDW                  

  _   QYPSJSVR    QYPSJSVR    343148  PGM-jvmStartPa     SIGW                  

  _   QJVACMDSRV  JOHNDOE     424242  JVM-MyJavaCls      THDW                  

  _   SERVER1     QEJBSVR     425212  PGM-jvmStartPa     THDW                  

  _   SERVER2     QEJBSVR     425341  PGM-jvmStartPa     THDW                  

                                                                                

                                                                         Bottom

 Parameters or command                                                         

 ===>__________________________________________________________________________

 F3=Exit   F4=Prompt   F5=Refresh    F6=Print     F9=Retrieve                  

 F11=Display subsystem information   F12=Cancel   F16=Resequence               

 

Among the first things you might notice are the system jobs. For instance, QSRVMON is a service monitor job that keeps an eye on the rest of the system, and QYPSJSVR is the support server for Management Central. IBM uses a lot of Java. Next on the list, you see a job running QJVACMDSRV; that's an example of a user job running Java. User JOHNDOE has executed the RUNJVA command, and this is the job that was submitted under the covers. Finally, you'll see a couple of server jobs. They're running under the QEJBSVR user profile, which means they're probably WebSphere server jobs. If you select one of these jobs with option 5, you'll get the Work With Java Virtual Machine display, which has a lot of Java-specific options.

 

                         Work with Java Virtual Machine                        

                                                             System:   MYI

   Job  . . . . . . :   QSRVMON             PID  . . . . . . :   11            

   User . . . . . . :   QSYS                JDK  . . . . . . :   1.6.0         

   Number . . . . . :   343115              Bits . . . . . . :   32            

                                                                               

 Select One of the following:                                                  

                                                                                

      1. Display JVM arguments                                                 

      2. Display environment variables                                         

      3. Display PASE environment variables                                     

      4. Display Java lock information                                         

      5. Display garbage collection information                                

      6. Display initial Java system properties                                 

      7. Display current Java system properties                                

      8. Display Java threads                                                  

      9. Display job log                                                        

     10. Display GC Cycle Table                                                

                                                                               

                                                                        More...

 Selection or command                                                          

 ===> _________________________________________________________________________

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

 

You can see the arguments used to initiate the JVM. Take a look at the environment variables for Java and for PASE and see the system properties, both when the job was first submitted and as they are currently defined. This information is far more useful to a Java developer than what the normal i5/OS tools can provide. Another option on the second page of the menu allows you to generate a Java dump, which sometimes is the only way to diagnose a Java problem.

 

Note that you don't have to go through WRKJVMJOB to get to this screen. If you happen to see a Java job when you're running WRKACTJOB, just select option 5 to run WRKJOB, and then from that menu, select the new option 45 to bring up the Work with Java Virtual Machine display above.

So Hello to the New Tools

Java is a different development environment and, as such, it needs new tools. Hopefully, the WRKJVMJOB command will be one of those tools that makes your Java development job a little easier.

 

 

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

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WDSC: Step by Step WDSC: Step by Step
Discover incredibly powerful WDSC with this easy-to-understand yet thorough introduction.
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Eclipse: Step by Step Eclipse: Step by Step
Quickly get up to speed and productivity using Eclipse.
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