Customizing Startup of the JVM Software

You might need to customize startup of the JVM software from dbx to do the following:

• Specify a path name for the JVM software (see Specifying a Path Name for the JVM Software)

• Pass some run arguments to the JVM software (see Passing Run Arguments to the JVM Software)

• Specify a custom wrapper instead of the default Java wrapper for running Java applications (see Specifying a Custom Wrapper for Your Java Application)

• Specify 64-bit JVM software (see Specifying 64-bit JVM Software)

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 -Xdebug -Xnoagent -Xrundbx_agent:syncpid

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

Specifying a Path Name for the JVM Software

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 in the following example.

jvm_invocation="/myjava/java -Xdebug"

This setting causes dbx to start the JVM software as follows:

/myjava/java -Djava.compiler=NONE -Xdebug -Xnoagent -Xrundbx_agent:sync

Passing Run Arguments to the JVM Software

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 causes dbx to start the JVM software as follows:

java -Djava.compiler=NONE -Xdebug -Xnoagent -Xrundbx_agent:sync= -Xms512 -Xmx1024 -Xcheck:jni

Specifying a Custom Wrapper for Your Java Application

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 in the following example.

jvm_invocation="/export/siva-a/forte4j/bin/forte4j.sh -J-Xdebug"

This causes dbx to start the JVM software as follows:

/export/siva-a/forte4j/bin/forte4j.sh - -J-Xdebug -J-Xnoagent -J-Xrundbxagent:sync=process_id

Using a Custom Wrapper That Accepts Command-Line Options

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 -Jany other java options"
% dbx myclass.class -Dide=visual

Using a Custom Wrapper That Does Not Accept Command-Line Options

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:

• You could 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.

• You could 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 made 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

Specifying 64-bit JVM Software

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"