You might need to customize startup of the JVM software from dbx to do certain tasks. Common tasks involving customization include the following::
You can customize startup of the JVM software using the jvm_invocation environment variable. By default, when the jvm_invocation environment variable is not defined, dbx starts the JVM software as follows
java -agentlib:dbx_agent=sync=process-ID
When the jvm_invocation environment variable is defined, dbx uses the value of the variable to start the JVM software.
You must include the -Xdebug option in the definition of the jvm_invocation environment variable. dbx expands -Xdebug into the internal options -Xdebug- Xnoagent -Xrundbxagent:sync.
If you do not include the -Xdebug option in the definition, as in the following example, dbx issues an error message.
jvm_invocation="/set/java/javasoft/sparc-S2/jdk1.2/bin/java"
dbx: Value of `$jvm_invocation’ must include an option to invoke the VM in debug mode
By default, dbx starts the JVM software in your path if you do not specify a path name for the JVM software.
To specify a path name for the JVM software, set the jvm_invocation environment variable to the appropriate path name, as shown in the following example.
jvm_invocation="/myjava/java -Xdebug"
This setting causes dbx to start the JVM software as follows:
/myjava/java –agentlib:dbx_agent=sync
To pass run arguments to the JVM software, set the jvm_invocation environment variable to start the JVM software with those arguments, as in the following example.
jvm_invocation="java -Xdebug -Xms512 -Xmx1024 -Xcheck:jni"
This example causes dbx to start the JVM software as follows:
java –agentlib:dbx_agent=sync= -Xms512 -Xmx1024 -Xcheck:jni
A Java application can use a custom wrapper for startup. If your application uses a custom wrapper, you can use the jvm_invocation environment variable to specify the wrapper to be used, as shown in the following example.
jvm_invocation="/export/siva-a/forte4j/bin/forte4j.sh -J-Xdebug"
This example causes dbx to start the JVM software as follows:
/export/siva-a/forte4j/bin/forte4j.sh - –agentlib:dbx_agent=sync=process-ID
The following wrapper script (xyz) sets a few environment variables and accepts command line options.
#!/bin/sh
CPATH=/mydir/myclass:/mydir/myjar.jar; export CPATH
JARGS="-verbose:gc -verbose:jni -DXYZ=/mydir/xyz"
ARGS=
while [ $# -gt 0 ] ; do
case "$1" in
-userdir) shift; if [ $# -gt 0 ]
; then userdir=$1; fi;;
-J*) jopt=`expr $1 : ’-J<.*>’`
; JARGS="$JARGS ’$jopt’";;
*) ARGS="$ARGS ’$1’" ;;
esac
shift
done
java $JARGS -cp $CPATH $ARGS
This script accepts some command-line options for the JVM software and the user application. For wrapper scripts of this form, you would set the jvm_invocation environment variable and start dbx as follows:
% jvm_invocation="xyz -J-Xdebug -J other-java-options" % dbx myclass.class -Dide=visual
The following wrapper script (xyz) sets a few environment variables and starts the JVM software, but does not accept any command-line options or a class name.
#!/bin/sh CLASSPATH=/mydir/myclass:/mydir/myjar.jar; export CLASSPATH ABC=/mydir/abc; export ABC java <options> myclass
You could use such a script to debug a wrapper using dbx in one of two ways:
Modify the script to start dbx from inside the wrapper script itself by adding the definition of the jvm_invocation variable to the script and starting dbx.
#!/bin/sh CLASSPATH=/mydir/myclass:/mydir/myjar.jar; export CLASSPATH ABC=/mydir/abc; export ABC jvm_invocation="java -Xdebug <options>"; export jvm_invocation dbx myclass.class
Once you have made this modification, you could start the debugging session by running the script.
Modify the script slightly to accept some command-line options as follows:
#!/bin/sh CLASSPATH=/mydir/myclass:/mydir/myjar.jar; export CLASSPATH ABC=/mydir/abc; export ABC JAVA_OPTIONS="$1 <options>" java $JAVA_OPTIONS $2
Once you make this modification, you would set the jvm_invocation environment variable and start dbx as follows:
% jvm_invocation="xyz -Xdebug"; export jvm_invocation % dbx myclass.class
If you want dbx to start 64-bit JVM software to debug an application that requires 64-bit object libraries, include the -d64 option when you set the jvm_invocation environment variable.
jvm_invocation="/myjava/java -Xdebug -d64"