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jdb: JavaTM Debugger
The jdb tool helps you find and fix bugs in JavaTM programs. For a complete description of the tool and its use, see the
Sun Microsystems documentation for jdb.
Synopsis
jdb [ options ]
Compaq Specifics
The Compaq implementation of the Java Debugger, jdb, differs slightly from the Sun Microsystems implementation. One
difference is in the way you start a jdb session. There are also some additional jdb commands, described under Compaq
Command Extensions.
Starting a jdb Session
There are two ways to use jdb for debugging. The most frequently used way is to have jdb start the java interpreter
with the class to be debugged. You do this by substituting the command jdb for the command java in the command line.
For example, to start a sample class named MyClass under jdb, use the following command:
# jdb MyClass
When started this way, jdb invokes a second Java interpreter with any specified parameters, loads the specified class, and
stops the interpreter before executing the first instruction of that class.
The second way to use jdb is to attach it to a Java interpreter that is already running. For security reasons, Java interpreters
can be debugged only if they have been started with the -Xdebug option. When started with the -Xdebug option, the
Java interpreter prints a password for use by jdb. In addition, the debugged interpreter must not be run with a JIT
compiler. Use the java option -Djava.compiler=NONE to disable the loading of any JIT compiler.
Special debugger classes must be available to the debugged interpreter. These classes are not part of the default run-time
class libraries. Use the java option
-Xbootclasspath:$INSTALL_DIR/jre/lib/tandemvm.jar:$INSTALL_DIR/jre/lib/rt.jar: \
$INSTALL_DIR/lib/tdmtools.jar:$INSTALL_DIR/lib/tools.jar
to allow the debugged interpreter to locate all necessary classes. It is important that tandemvm.jar appear before
rt.jar and that tdmtools.jar appear before tools.jar. $INSTALL_DIR is the directory where java has been
installed. To summarize, launch the Java interpreter as follows:
# java -Xdebug -XDjava.compiler=NONE
-Xbootclasspath:$INSTALL_DIR/jre/lib/tandemvm.jar: \
$INSTALL_DIR/jre/lib/rt.jar:$INSTALL_DIR/lib/tdmtools.jar:$INSTALL_DIR/lib/tools.jar
To attach jdb to a running Java interpreter (when the session password is known), invoke it as follows:
# jdb -host hostname -password password
For jdb to be attached to the running Java interpreter, the code in your Java class must relinquish control occasionally (at
least). This is because the threads in NonStopTM Server for Java are not preemptive; that is, a thread runs until it explicitly
gives up control. A call to Thread.sleep or Thread.yield causes the thread to relinquish control, as does an I/O
operation to another process (such as a Pathsend call or a socket call), but a SQL call by means of JDBC does not
relinquish control of the thread.
The jdb tool cannot be used to debug Java code that reads input from the terminal.
Compaq Command Extensions
The following are Compaq extensions to the basic jdb commands. The Java Debugger supports other commands that you
can list with the jdb help command.
obey filename
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