Java Locks Profiling

Java Locks Profiling

The information that is displayed under the Java Locks chart (Figure 13-2) shows the number of locks of the threads in your application. You see information on the number of fat uncontended and contended locks, thin uncontended and contended locks, thin and fat recursive locks, and fat sleeping locks. For more information on locks, please refer to About Thin, Fat, Recursive, and Contended Locks in BEA JRockit.

Use the filtering function to find the Java locks you are looking for, see Filtering Information.

Figure 13-2 Java Locks

Enabling Java Lock Profiling Data

To record Java lock profiling data, you need to enable it from the command line when you start JRockit. If your the Java Locks table is blank, it is not enabled.

To enable Java lock profiling data

Issue the command -Djrockit.lockprofiling at the JRockit command line.

For example:

java -Djrockit.lockprofiling=true -XXjra:<AnyJRAParam> -jar MyApplication.jar

Showing Classes Banned from Lazy Unlocking

You can show classes that have been banned from lazy unlocking in the Java Locks table; however, the Banned Classes column is hidden by default. This column shows that the class/type has been banned for lazy unlocking"

To unhide the Banned Classes column

Open the Filter Column drop-down list and select Lazy Banned, as shown in Figure 13-3.

Figure 13-3 Selecting Lazy Banned

Selecting Lazy Banned

Java Lock Profiling Overhead

If you enable Java Lock profiling with the system property -Djrockit.lockprofiling=true the overhead could be considerable greater, typically between 3% and 25% depending upon the application.