Disable TraceClassUnloading in Java 6

I recently discovered logs filling up with log messages for classes being unloaded during garbage collection. After a little research, I found that the TraceClassUnloading switch gets turned on by the Xloggc switch. After a little testing, I found that this can be resolved by adding the argument -XX:-TraceClassUnloading after the -Xloggc argument.

This problem occurs with the Sun Java 6 JDK but appears resolved in the Java 7 JDK. Other JDKs may use different flags and may not have the same behavior.

I have included my test class and script if you want to run your own tests. The final option resolves the problem.

Test Class

To test the settings I created a minimal Java program that sleeps 15 seconds. This allows time to examine the final Java flags. Any program which runs for several seconds could be used.

public class Sleep15 {
    /** Sleeps 15 seconds and exits.
     */
    public static void main(String[] args) {
        try {
            Thread. sleep(15 * 1000);
        } catch (InterruptedException e) {
            // e.printStackTrace();
        }
    }
}

Test Script

The following test script checks the above program with three sets of arguments.  The JAVA_HOME variable is used to determine the JDK to test.

#!/bin/bash
echo "Java_home: ${JAVA_HOME}"

for OPTS in ' '  '-XX:-TraceClassUnloading -Xloggc:gc.log' \
               '-Xloggc:gc.log -XX:-TraceClassUnloading'; do
     echo -e "\nOPTS: ${OPTS}"
     ${JAVA_HOME}/bin/java ${OPTS} Sleep15 &
     sleep 5
     ${JAVA_HOME}/bin/jinfo -flag TraceClassUnloading $!
     kill $!
done