Sometimes it may seem hard to get a simple thread stack dump from your JRockit. You may for instance have started it using the -Xnohup (-Xrs) option, or as a service. I’ll list three different ways of looking at your threads in such situations.

The first way of getting your thread dump is to use jrcmd. My previous blog shows some basic jrcmd usage, so I’ll just mention the command name: print_threads. Basic usage is jrcmd <PID> print_threads, for example jrcmd 780 print_threads.

The second way is to simply start the management console on the JRockit you want to monitor. After connecting the console to the JVM and switching to the threads view, you should be looking at something similar to the screen shot below.

The third way is to use the MBean Browser’s capability to invoke arbitrary operations on MBeans (also described in the last blog). Go to the MBean Browser in the JRockit Management Console. Select the DiagnosticCommand MBean, and switch to the operations tab. Select the execute operation that takes a String argument and returns a String. Click the String button, and fill in the argument print_threads.

When you execute the operation you should see something like this:

There are also ways of doing this programmatically, for example by using the JRockit JMAPI, or by invoking the execute operation programmatically as described in another old blog.

Exception profiling is the business of finding out what exceptions are being thrown within your application and from where. In JRockit Mission Control you can find out how many exceptions have been thrown using JRA, and you can count the exceptions using the JRockit Management Console. Sadly there is no way of doing powerful exception profiling (i.e. looking at the stack traces for the exceptions, aggregating them and visualizing them directly in the JRockit Mission Control Client) just yet. This will be incorporated in a future version of Mission Control.

There is fortunately a way to do exception profiling with JRockit today. There are exception related verbose flags available in JRockit. These are examples on how to use them:

java -Xverbose:exceptions=debug …

java -Xverbose:exceptions=trace …

For a list of valid verbose options, please see http://e-docs.bea.com/jrockit/jrdocs/refman/optionX.html#wp999543.

Sometimes you really just want to enable this profiling for a little while, for example to avoid cluttering your log files. Then there is a nifty tool for JRockit called jrcmd you can use to turn on/off the exception profiling. It can be found under JROCKIT_HOME\bin\.

First use jrcmd to list all running java processes. Here is an example of what it may look like:

>jrcmd

10984 jrockit.tools.jrcmd.JrCmd

9396 C:\Java\eclipse3.3.1.1\plugins\org.eclipse.equinox.launcher_1.0.1.R33x_v200
70828.jar -data D:\Data\workspaces\workspace_3.3_facade -os win32 -ws win32 -arc
h x86 -showsplash -launcher C:\Java\eclipse3.3.1.1\eclipse.exe -name Eclipse –l
auncher.library C:\Java\eclipse3.3.1.1\plugins\org.eclipse.equinox.launcher.win3
2.win32.x86_1.0.2.R331_v20071019\eclipse_1021.dll -startup C:\Java\eclipse3.3.1.
1\plugins\org.eclipse.equinox.launcher_1.0.1.R33x_v20070828.jar -exitdata 1908_7
c -vm D:\jrockits\R27.4.0_R27.4.0-90_1.5.0\bin\javaw.exe -vmargs -Xms256m -Xmx51
2m -XgcPrio:deterministic -XpauseTarget:40 -Dosgi.bundlefile.limit=100 -jar C:\J
ava\eclipse3.3.1.1\plugins\org.eclipse.equinox.launcher_1.0.1.R33x_v20070828.jar

10976 Gegga

The numbers are the PIDs of the processes, and are used as the first argument to jrcmd to specify on what JRockit to address. You can use jrcmd to check what commands are available. Here is an example:

>jrcmd 10976 help
10976:
The following commands are available:
        kill_rmp_server
        start_rmp_server
        kill_management_server
        start_management_server
        checkjrarecording
        stopjrarecording
        startjrarecording
        print_object_summary
        memleakserver
        print_codegenlist
        print_class_summary
        run_optfile
        dump_codelayout
        dump_codelist
        dump_codemap
        print_utf8pool
        print_properties
        print_threads
        datadump_request
        runsystemgc
        runfinalization
        heap_diagnostics
        oom_diagnostics
        print_exceptions
        version
        timestamp
        command_line
        memprof
        sanity
        verbosity
        set_filename
        help
        print_memusage
For more information about a specific command use ‘help <command>’.
Parameters to commands are optional unless otherwise stated.

Let’s get more information about the print_exceptions command:

>jrcmd 10976 help print_exceptions

10976:
Enable printing of Java exceptions thrown in the VM.
To turn exception printing off completely you need to set exceptions = false
even if it was turned on by stacktraces = true. NOTE: This handler is
deprecated. The preferred way of displaying exceptions is to use the
‘exceptions’ logging module: -Xverbose:exceptions.
Values for the parameters can be "true|all|false"
true  – print all exception except java/util/EmptyStackException,
java/lang/ClassNotFoundException and
java/security/PrivilegedActionException
all   – print all exception
false – don’t print exceptions
        exceptions  – print exceptions (string, false)
        stacktraces – print stacktrace (string, false)

Never mind that it is using an old handler in R27.6. The functionality will be the same. Let’s enable the exception profiling:

>jrcmd 10976 print_exceptions stacktraces=true

If your application is throwing exceptions, you should now be seeing traces being logged to the console of that application. To turn off the exception logging, we do as the help suggests:

>jrcmd 10976 print_exceptions exceptions=false

Now, an even easier way to access the jrockit diagnostic commands is to use the JRockit Management Console. Simply connect the JRockit Management Console to the JRockit you wish to enable exception profiling on (from JRockit Mission Control). (Click the images to look at them in full size.)

Once the console is started, open the MBean Browser tab and move to the DiagnosticCommand MBean under bea.jrockit.management:

Double clicking on the ArrayList value of AllCommands will open up a list of all the available commands:

 
Now, select the operations tab and the executeDefault method that takes a String argument and press invoke. This will provide you with a dialog with push buttons for the arguments. In this case a single button with the label String. Press the String button and fill out the command. For example, print_exceptions stacktraces=true.

Press Ok on both of the dialogs and exception profiling should now be enabled. To turn it off again, just invoke the operation again and enter print_exceptions exceptions=false, analogously with how you would use jrcmd.

An even easier way for Oracle employees is to pick up a recent internal build of JRockit and use the Diagnostic Command tab in the JRockit Management Console. 🙂 Soon coming to a JRockit near you!

Here is an interesting blog entry regarding the Oracle acquisition of BEA:

http://theabstracttruth.wordpress.com/2008/06/12/t3server-tengah-bea-wls-and-now-oracle-weblogic/

The next version of JRockit Mission Control just went live! Feature-wise it is only a minor upgrade, I will go into detail about the most exciting one in a bit, but there are some other changes to this release that are quite profound.

The, in my humble opinion, greatest change is that all JRockit Mission Control features are available by default. There is no need to dabble with licenses. Everything is free to use for evaluation, which among other things means that you can now try out the latency analyzer properly.

JRockit Mission Control has also been relocated to a new homepage at OTN, located at http://www.oracle.com/technology/products/jrockit/missioncontrol/index.html. The next few days a lot of new JRockit Mission Control related material will be posted there.

The update site has moved as well, and can now be found at http://www.oracle.com/technology/software/products/jrockit/missioncontrol/updates/eclipse-3.3/jrmc/.

As you will undoubtedly notice, everything has also been re-branded.

Now, the cool new feature is actually a JRockit JVM side upgrade, that will be automatically picked up by the JRockit Mission Control client. It is now possible to do very cheap memory allocation profiling using the JRockit Latency Analyzer.

There is a new type of latency events available in the latency recordings. They are triggered whenever the JRockit JVM needs to acquire a new Thread Local Area or whenever the JRockit JVM needs to allocate a new large object. These events provides a good approximation to what is causing the most pressure on the memory system. This means that it is quite easy to find out where to start optimizing allocation behaviour using JRMC LAT.

Here is an example:

1. First select the JVM you wish to start a JRA recording on.
   
2. In the JRA recording wizard, ensure that you start a JRA recording with latency information in it.
   You can for example use the Latency Recording Template.
   
3. Then open the Latency Log tab and open a histogram over the events.
   Make the histogram over the Object Allocation – Class Name property by selecting it in the second combo box.
    
   Note: since the allocation events aren’t recognized yet as being from the standard producer, you may need to enable them in the event palette to the left.As you can see, most of the pressure on the memory system seems to be from the allocations of Strings. This is not uncommon. Together with arrays of primitive types, Strings are quite commonly high ranking here.
4. Now right click on the String row in the table, and set the operative set to the events corresponding to that row.
   The selected event property will unfortunately be reset, which will cause the histogram to be reset as well, but never mind that.
5. Move over to the Latency Traces view and check that you only want to see the events in the operative set.
    
   You can now clearly see exactly where you need to reduce the amount of String allocation to reduce the pressure on the memory system.

Reducing the pressure on the memory system leads to less frequent garbage collections and thus a more responsive system.

For more information on the JRockit JVM R27.6 release, please have a look at the release notes.

Just stumbled across this article on the common ground and differences between DSDM and Scrum:

http://www.dsdm.org/timebox/issue32/DSDM&Scrum.asp

I’ve always held DSDM close at heart, as DSDM was my very first contact with the ideas that sparked the agile revolution.

As most seasoned Agile practitioners, I tend to practice neither DSMD nor Scrum but rather whatever blend of the different Agile methods or frameworks that happens to suit the current situation. Still, DSDM contains a lot of good material and white papers for using the approach in less common situations, as well as good tips on how to manage risks when using agile approaches in difficult situations, such a geographically disparate teams.

Recommended reading! 🙂

The people over at eclipseusers.se have put together a meeting. The meeting will take place the 17th of June, 16:00 at Cinnober Financial Technology. For more information:  http://www.eclipseusers.se/forum/showthread.php?p=29