source: trunk/gcc/libjava/java/lang/VMThrowable.java

/* java.lang.VMThrowable -- VM support methods for Throwable.
   Copyright (C) 1998, 1999, 2002 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GNU Classpath is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Classpath; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
conditions of the GNU General Public License cover the whole
combination.

As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
modules, and to copy and distribute the resulting executable under
terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
module.  An independent module is a module which is not derived from
or based on this library.  If you modify this library, you may extend
this exception to your version of the library, but you are not
obligated to do so.  If you do not wish to do so, delete this
exception statement from your version. */

package java.lang;

import gnu.gcj.runtime.NameFinder;
import gnu.gcj.runtime.StackTrace;

/**
 * VM dependent state and support methods Throwable.
 * It is deliberately package local and final and should only be accessed
 * by the Throwable class.
 * <p>
 * This is the version used by libgcj (http://gcc.gnu.org/java/).
 *
 * @author Mark Wielaard (mark@klomp.org)
 */
final class VMThrowable
{
  private gnu.gcj.runtime.StackTrace trace;

  /**
   * Private contructor, create VMThrowables with fillInStackTrace();
   */
  private VMThrowable() { }

  /**
   * Fill in the stack trace with the current execution stack.
   * Called by <code>Throwable.fillInStackTrace()</code> to get the state of
   * the VM. Can return null when the VM does not support caputing the VM
   * execution state.
   *
   * @return a new VMThrowable containing the current execution stack trace.
   * @see Throwable#fillInStackTrace()
   */
  static VMThrowable fillInStackTrace(Throwable t)
  {
    VMThrowable state = null;
    
    /* FIXME: size of the stack trace is limited to 128 elements.
       It's undoubtedly sensible to limit the stack trace, but 128 is
       rather arbitrary.  It may be better to configure this.  */
    if (trace_enabled)
      {
        state = new VMThrowable ();
        state.trace = new gnu.gcj.runtime.StackTrace(128);
      }
    return state;
  }

  /**
   * Returns an <code>StackTraceElement</code> array based on the execution
   * state of the VM as captured by <code>fillInStackTrace</code>.
   * Called by <code>Throwable.getStackTrace()</code>.
   *
   * @return a non-null but possible zero length array of StackTraceElement.
   * @see Throwable#getStackTrace()
   */
  StackTraceElement[] getStackTrace(Throwable t)
  {
    StackTraceElement[] result;
    if (trace != null)
      {
        NameFinder nameFinder = new NameFinder();
        result = nameFinder.lookup(t, trace.stackTraceAddrs(), 
                                   trace.length());
        nameFinder.close();
      }
    else
      result = new StackTraceElement[0];

    return result;
  }

  // Setting this flag to false prevents fillInStackTrace() from running.
  static boolean trace_enabled = true;
}