Name: joT67522 Date: 08/26/97


sun.tools.debug.RemoteThread.getCurrentFrame does not reliably
return the correct stack frame information unless
RemoteThread.dumpStack has been called.

----- TEST CASE:
Run the following Java program, Mdbg:

-------
// Sample code to illustrate use of RemoteDebugger APIs
// Author: Malcom Zung 1997

import sun.tools.debug.*;
import java.io.*;

class Mdbg implements DebuggerCallback {

  // Data Members

  protected RemoteDebugger debugger_;
  protected RemoteThread currentThread_;
  private final String debuggeeName = "howdy";
  private final boolean consoleOutput = false;

  // Mdbg methods

  public Mdbg() {
  }

  protected synchronized void debug() {
    int i = 0;

    try {
      debugOutput("Creating new debugger...");
      debugger_ = new RemoteDebugger("", this, true);

      debugOutput("Looking up start class...");
      RemoteClass startClass = debugger_.findClass(debuggeeName);
      debugOutput("startClass = " + startClass);

      debugOutput("Looking up main method...");
      RemoteField mainMethod = startClass.getMethod("main");
      debugOutput("mainMethod = " + mainMethod);

      debugOutput("Set breakpoint in main method...");
      startClass.setBreakpointMethod(mainMethod);

      debugOutput("Go...");
      String[] parms = { debuggeeName, "parm1" };
      debugger_.run(1, parms);
      wait();
      printStackFrame(currentThread_);

      /*
      debugOutput("Getting threadgroups...");
      RemoteThreadGroup[] threadGroups = debugger_.listThreadGroups(null);
      for (i=0; i<threadGroups.length; ++i)
debugOutput("threadGroups[" + i + "] = " + threadGroups[i]);
      */

      debugOutput("Stepping over...");
      currentThread_.next();
      wait();
      printStackFrame(currentThread_);
      printStackFrame(currentThread_);


      debugOutput("Closing debugger...");
      debugger_.close();
    }
    catch(Exception excp) {
      handleException(excp);
    }
  }

  static public void main(String[] args) {
    Mdbg mdb = new Mdbg();
    mdb.debug();
  }

  protected void printStackFrame(RemoteThread thd) {
    try {
      debugOutput("Thread = " + thd);
      RemoteStackFrame currentStackFrame = thd.getCurrentFrame();
      debugOutput("StackFrame (getCurrentFrame) = " + currentStackFrame);

      RemoteStackFrame[] currentStackFrame1 = thd.dumpStack();
      debugOutput("StackFrame (dumpStack) = " + currentStackFrame1[0]);
    }
    catch(Exception excp) {
      handleException(excp);
    }
  }

  protected void handleException(Exception excp) {
    System.out.println("*** Error: exception thrown." + excp);
    System.out.println(excp.getMessage());
    excp.printStackTrace();
    debugger_.close();
    System.exit(1);
  }

  protected void debugOutput(String msg) {
    System.out.println("Mdbg> " + msg);
  }

  // Debugger Callback methods

  public void printToConsole(String msg) {
    if (consoleOutput)
      System.out.println("Console> " + msg);
  }

  public synchronized void breakpointEvent(RemoteThread thd) {
    debugOutput("breakpointEvent() called.");
    currentThread_ = thd;
    notify();
  }

  public void exceptionEvent(RemoteThread thd, String err) {
    debugOutput("exceptionEvent() called.");
  }

  public void threadDeathEvent(RemoteThread thd) {
    debugOutput("threadDeathEvent() called.");
  }

  public void quitEvent() {
    debugOutput("quitEvent() called.");
  }
}
-------

This program looks for a class called "howdy" to debug.
I used the following program:

------
class howdy
{
  public static void
  main( String argv[] )
  {
    int i = 0;
    ++i;
    ++i;

    System.out.println( "Howdy there yall!" );
    System.out.println( "The value of i is: " + i );
    System.out.println( "I don't have anything more to say!" );
  }
}

--------

When this is run, the following output is produced:

D:\java\dbgtest>java Mdbg
Mdbg> Creating new debugger...
[debugger: starting child: D:\JDK1.1.2\BIN\..\bin\java_g -debug sun.tools.debug
.EmptyApp]
[debugger: password returned: 5kf6mb]
Mdbg> Looking up start class...
Mdbg> startClass = 0xf709a0:class(howdy)
Mdbg> Looking up main method...
Mdbg> mainMethod = ([Ljava/lang/String;)V main
Mdbg> Set breakpoint in main method...
Mdbg> Go...
Mdbg> breakpointEvent() called.
Mdbg> Thread = Thread[main,5,howdy.main]
Mdbg> StackFrame (getCurrentFrame) = howdy.main (howdy:8)
Mdbg> StackFrame (dumpStack) = howdy.main (howdy:8)
Mdbg> Stepping over...
Mdbg> breakpointEvent() called.
Mdbg> Thread = Thread[main,5,howdy.main]
Mdbg> StackFrame (getCurrentFrame) = howdy.main (howdy:8) ***
Mdbg> StackFrame (dumpStack) = howdy.main (howdy:9)
Mdbg> Thread = Thread[main,5,howdy.main]
Mdbg> StackFrame (getCurrentFrame) = howdy.main (howdy:9)
Mdbg> StackFrame (dumpStack) = howdy.main (howdy:9)
Mdbg> Closing debugger...

Notice that the line number information on the line marked with
*** is not correct. getCurrentFrame does not return the correct
information until after dumpStack has been called.

company - IBM Canada , email - ###@###.###
======================================================================