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.
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
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
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
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
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.