src/share/classes/com/sun/tools/jdi/StackFrameImpl.java - platform/external/oj-libjdwp - Git at Google

 /*
  * Copyright (c) 1998, 2008, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 only, as
  * published by the Free Software Foundation.  Oracle designates this
  * particular file as subject to the "Classpath" exception as provided
  * by Oracle in the LICENSE file that accompanied this code.
  *
  * This code 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
  * version 2 for more details (a copy is included in the LICENSE file that
  * accompanied this code).
  *
  * You should have received a copy of the GNU General Public License version
  * 2 along with this work; if not, write to the Free Software Foundation,
  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  *
  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  * or visit www.oracle.com if you need additional information or have any
  * questions.
  */

 package com.sun.tools.jdi;

 import com.sun.jdi.*;

 import java.util.List;
 import java.util.Map;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashMap;
 import java.util.Iterator;
 import java.util.Collections;

 public class StackFrameImpl extends MirrorImpl
                             implements StackFrame, ThreadListener
 {
     /* Once false, frame should not be used.
      * access synchronized on (vm.state())
      */
     private boolean isValid = true;

     private final ThreadReferenceImpl thread;
     private final long id;
     private final Location location;
     private Map<String, LocalVariable> visibleVariables =  null;
     private ObjectReference thisObject = null;

     StackFrameImpl(VirtualMachine vm, ThreadReferenceImpl thread,
                    long id, Location location) {
         super(vm);
         this.thread = thread;
         this.id = id;
         this.location = location;
         thread.addListener(this);
     }

     /*
      * ThreadListener implementation
      * Must be synchronized since we must protect against
      * sending defunct (isValid == false) stack ids to the back-end.
      */
     public boolean threadResumable(ThreadAction action) {
         synchronized (vm.state()) {
             if (isValid) {
                 isValid = false;
                 return false;   /* remove this stack frame as a listener */
             } else {
                 throw new InternalException(
                                   "Invalid stack frame thread listener");
             }
         }
     }

     void validateStackFrame() {
         if (!isValid) {
             throw new InvalidStackFrameException("Thread has been resumed");
         }
     }

     /**
      * Return the frame location.
      * Need not be synchronized since it cannot be provably stale.
      */
     public Location location() {
         validateStackFrame();
         return location;
     }

     /**
      * Return the thread holding the frame.
      * Need not be synchronized since it cannot be provably stale.
      */
     public ThreadReference thread() {
         validateStackFrame();
         return thread;
     }

     public boolean equals(Object obj) {
         if ((obj != null) && (obj instanceof StackFrameImpl)) {
             StackFrameImpl other = (StackFrameImpl)obj;
             return (id == other.id) &&
                    (thread().equals(other.thread())) &&
                    (location().equals(other.location())) &&
                     super.equals(obj);
         } else {
             return false;
         }
     }

     public int hashCode() {
         return (thread().hashCode() << 4) + ((int)id);
     }

     public ObjectReference thisObject() {
         validateStackFrame();
         MethodImpl currentMethod = (MethodImpl)location.method();
         if (currentMethod.isStatic() || currentMethod.isNative()) {
             return null;
         } else {
             if (thisObject == null) {
                 PacketStream ps;

                 /* protect against defunct frame id */
                 synchronized (vm.state()) {
                     validateStackFrame();
                     ps = JDWP.StackFrame.ThisObject.
                                       enqueueCommand(vm, thread, id);
                 }

                 /* actually get it, now that order is guaranteed */
                 try {
                     thisObject = JDWP.StackFrame.ThisObject.
                                       waitForReply(vm, ps).objectThis;
                 } catch (JDWPException exc) {
                     switch (exc.errorCode()) {
                     case JDWP.Error.INVALID_FRAMEID:
                     case JDWP.Error.THREAD_NOT_SUSPENDED:
                     case JDWP.Error.INVALID_THREAD:
                         throw new InvalidStackFrameException();
                     default:
                         throw exc.toJDIException();
                     }
                 }
             }
         }
         return thisObject;
     }

     /**
      * Build the visible variable map.
      * Need not be synchronized since it cannot be provably stale.
      */
     private void createVisibleVariables() throws AbsentInformationException {
         if (visibleVariables == null) {
             List<LocalVariable> allVariables = location.method().variables();
             Map<String, LocalVariable> map = new HashMap<String, LocalVariable>(allVariables.size());

             for (LocalVariable variable : allVariables) {
                 String name = variable.name();
                 if (variable.isVisible(this)) {
                     LocalVariable existing = map.get(name);
                     if ((existing == null) ||
                         ((LocalVariableImpl)variable).hides(existing)) {
                         map.put(name, variable);
                     }
                 }
             }
             visibleVariables = map;
         }
     }

     /**
      * Return the list of visible variable in the frame.
      * Need not be synchronized since it cannot be provably stale.
      */
     public List<LocalVariable> visibleVariables() throws AbsentInformationException {
         validateStackFrame();
         createVisibleVariables();
         List<LocalVariable> mapAsList = new ArrayList<LocalVariable>(visibleVariables.values());
         Collections.sort(mapAsList);
         return mapAsList;
     }

     /**
      * Return a particular variable in the frame.
      * Need not be synchronized since it cannot be provably stale.
      */
     public LocalVariable visibleVariableByName(String name) throws AbsentInformationException  {
         validateStackFrame();
         createVisibleVariables();
         return visibleVariables.get(name);
     }

     public Value getValue(LocalVariable variable) {
         List<LocalVariable> list = new ArrayList<LocalVariable>(1);
         list.add(variable);
         return getValues(list).get(variable);
     }

     public Map<LocalVariable, Value> getValues(List<? extends LocalVariable> variables) {
         validateStackFrame();
         validateMirrors(variables);

         int count = variables.size();
         JDWP.StackFrame.GetValues.SlotInfo[] slots =
                            new JDWP.StackFrame.GetValues.SlotInfo[count];

         for (int i=0; i<count; ++i) {
             LocalVariableImpl variable = (LocalVariableImpl)variables.get(i);
             if (!variable.isVisible(this)) {
                 throw new IllegalArgumentException(variable.name() +
                                  " is not valid at this frame location");
             }
             slots[i] = new JDWP.StackFrame.GetValues.SlotInfo(variable.slot(),
                                       (byte)variable.signature().charAt(0));
         }

         PacketStream ps;

         /* protect against defunct frame id */
         synchronized (vm.state()) {
             validateStackFrame();
             ps = JDWP.StackFrame.GetValues.enqueueCommand(vm, thread, id, slots);
         }

         /* actually get it, now that order is guaranteed */
         ValueImpl[] values;
         try {
             values = JDWP.StackFrame.GetValues.waitForReply(vm, ps).values;
         } catch (JDWPException exc) {
             switch (exc.errorCode()) {
                 case JDWP.Error.INVALID_FRAMEID:
                 case JDWP.Error.THREAD_NOT_SUSPENDED:
                 case JDWP.Error.INVALID_THREAD:
                     throw new InvalidStackFrameException();
                 default:
                     throw exc.toJDIException();
             }
         }

         if (count != values.length) {
             throw new InternalException(
                       "Wrong number of values returned from target VM");
         }
         Map<LocalVariable, Value> map = new HashMap<LocalVariable, Value>(count);
         for (int i=0; i<count; ++i) {
             LocalVariableImpl variable = (LocalVariableImpl)variables.get(i);
             map.put(variable, values[i]);
         }
         return map;
     }

     public void setValue(LocalVariable variableIntf, Value valueIntf)
         throws InvalidTypeException, ClassNotLoadedException {

         validateStackFrame();
         validateMirror(variableIntf);
         validateMirrorOrNull(valueIntf);

         LocalVariableImpl variable = (LocalVariableImpl)variableIntf;
         ValueImpl value = (ValueImpl)valueIntf;

         if (!variable.isVisible(this)) {
             throw new IllegalArgumentException(variable.name() +
                              " is not valid at this frame location");
         }

         try {
             // Validate and convert value if necessary
             value = ValueImpl.prepareForAssignment(value, variable);

             JDWP.StackFrame.SetValues.SlotInfo[] slotVals =
                 new JDWP.StackFrame.SetValues.SlotInfo[1];
             slotVals[0] = new JDWP.StackFrame.SetValues.
                                        SlotInfo(variable.slot(), value);

             PacketStream ps;

             /* protect against defunct frame id */
             synchronized (vm.state()) {
                 validateStackFrame();
                 ps = JDWP.StackFrame.SetValues.
                                      enqueueCommand(vm, thread, id, slotVals);
             }

             /* actually set it, now that order is guaranteed */
             try {
                 JDWP.StackFrame.SetValues.waitForReply(vm, ps);
             } catch (JDWPException exc) {
                 switch (exc.errorCode()) {
                 case JDWP.Error.INVALID_FRAMEID:
                 case JDWP.Error.THREAD_NOT_SUSPENDED:
                 case JDWP.Error.INVALID_THREAD:
                     throw new InvalidStackFrameException();
                 default:
                     throw exc.toJDIException();
                 }
             }
         } catch (ClassNotLoadedException e) {
             /*
              * Since we got this exception,
              * the variable type must be a reference type. The value
              * we're trying to set is null, but if the variable's
              * class has not yet been loaded through the enclosing
              * class loader, then setting to null is essentially a
              * no-op, and we should allow it without an exception.
              */
             if (value != null) {
                 throw e;
             }
         }
     }

     public List<Value> getArgumentValues() {
         validateStackFrame();
         MethodImpl mmm = (MethodImpl)location.method();
         List<String> argSigs = mmm.argumentSignatures();
         int count = argSigs.size();
         JDWP.StackFrame.GetValues.SlotInfo[] slots =
                            new JDWP.StackFrame.GetValues.SlotInfo[count];

         int slot;
         if (mmm.isStatic()) {
             slot = 0;
         } else {
             slot = 1;
         }
         for (int ii = 0; ii < count; ++ii) {
             char sigChar = argSigs.get(ii).charAt(0);
             slots[ii] = new JDWP.StackFrame.GetValues.SlotInfo(slot++,(byte)sigChar);
             if (sigChar == 'J' || sigChar == 'D') {
                 slot++;
             }
         }

         PacketStream ps;

         /* protect against defunct frame id */
         synchronized (vm.state()) {
             validateStackFrame();
             ps = JDWP.StackFrame.GetValues.enqueueCommand(vm, thread, id, slots);
         }

         ValueImpl[] values;
         try {
             values = JDWP.StackFrame.GetValues.waitForReply(vm, ps).values;
         } catch (JDWPException exc) {
             switch (exc.errorCode()) {
                 case JDWP.Error.INVALID_FRAMEID:
                 case JDWP.Error.THREAD_NOT_SUSPENDED:
                 case JDWP.Error.INVALID_THREAD:
                     throw new InvalidStackFrameException();
                 default:
                     throw exc.toJDIException();
             }
         }

         if (count != values.length) {
             throw new InternalException(
                       "Wrong number of values returned from target VM");
         }
         return Arrays.asList((Value[])values);
     }

     void pop() throws IncompatibleThreadStateException {
         validateStackFrame();
         // flush caches and disable caching until command completion
         CommandSender sender =
             new CommandSender() {
                 public PacketStream send() {
                     return JDWP.StackFrame.PopFrames.enqueueCommand(vm,
                                  thread, id);
                 }
         };
         try {
             PacketStream stream = thread.sendResumingCommand(sender);
             JDWP.StackFrame.PopFrames.waitForReply(vm, stream);
         } catch (JDWPException exc) {
             switch (exc.errorCode()) {
             case JDWP.Error.THREAD_NOT_SUSPENDED:
                 throw new IncompatibleThreadStateException(
                          "Thread not current or suspended");
             case JDWP.Error.INVALID_THREAD:   /* zombie */
                 throw new IncompatibleThreadStateException("zombie");
             case JDWP.Error.NO_MORE_FRAMES:
                 throw new InvalidStackFrameException(
                          "No more frames on the stack");
             default:
                 throw exc.toJDIException();
             }
         }

         // enable caching - suspended again
         vm.state().freeze();
     }

     public String toString() {
        return location.toString() + " in thread " + thread.toString();
     }
 }
	/*
	* Copyright (c) 1998, 2008, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code 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
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package com.sun.tools.jdi;

	import com.sun.jdi.*;

	import java.util.List;
	import java.util.Map;
	import java.util.ArrayList;
	import java.util.Arrays;
	import java.util.HashMap;
	import java.util.Iterator;
	import java.util.Collections;

	public class StackFrameImpl extends MirrorImpl
	implements StackFrame, ThreadListener
	{
	/* Once false, frame should not be used.
	* access synchronized on (vm.state())
	*/
	private boolean isValid = true;

	private final ThreadReferenceImpl thread;
	private final long id;
	private final Location location;
	private Map<String, LocalVariable> visibleVariables = null;
	private ObjectReference thisObject = null;

	StackFrameImpl(VirtualMachine vm, ThreadReferenceImpl thread,
	long id, Location location) {
	super(vm);
	this.thread = thread;
	this.id = id;
	this.location = location;
	thread.addListener(this);
	}

	/*
	* ThreadListener implementation
	* Must be synchronized since we must protect against
	* sending defunct (isValid == false) stack ids to the back-end.
	*/
	public boolean threadResumable(ThreadAction action) {
	synchronized (vm.state()) {
	if (isValid) {
	isValid = false;
	return false; /* remove this stack frame as a listener */
	} else {
	throw new InternalException(
	"Invalid stack frame thread listener");
	}
	}
	}

	void validateStackFrame() {
	if (!isValid) {
	throw new InvalidStackFrameException("Thread has been resumed");
	}
	}

	/**
	* Return the frame location.
	* Need not be synchronized since it cannot be provably stale.
	*/
	public Location location() {
	validateStackFrame();
	return location;
	}

	/**
	* Return the thread holding the frame.
	* Need not be synchronized since it cannot be provably stale.
	*/
	public ThreadReference thread() {
	validateStackFrame();
	return thread;
	}

	public boolean equals(Object obj) {
	if ((obj != null) && (obj instanceof StackFrameImpl)) {
	StackFrameImpl other = (StackFrameImpl)obj;
	return (id == other.id) &&
	(thread().equals(other.thread())) &&
	(location().equals(other.location())) &&
	super.equals(obj);
	} else {
	return false;
	}
	}

	public int hashCode() {
	return (thread().hashCode() << 4) + ((int)id);
	}

	public ObjectReference thisObject() {
	validateStackFrame();
	MethodImpl currentMethod = (MethodImpl)location.method();
	if (currentMethod.isStatic() \|\| currentMethod.isNative()) {
	return null;
	} else {
	if (thisObject == null) {
	PacketStream ps;

	/* protect against defunct frame id */
	synchronized (vm.state()) {
	validateStackFrame();
	ps = JDWP.StackFrame.ThisObject.
	enqueueCommand(vm, thread, id);
	}

	/* actually get it, now that order is guaranteed */
	try {
	thisObject = JDWP.StackFrame.ThisObject.
	waitForReply(vm, ps).objectThis;
	} catch (JDWPException exc) {
	switch (exc.errorCode()) {
	case JDWP.Error.INVALID_FRAMEID:
	case JDWP.Error.THREAD_NOT_SUSPENDED:
	case JDWP.Error.INVALID_THREAD:
	throw new InvalidStackFrameException();
	default:
	throw exc.toJDIException();
	}
	}
	}
	}
	return thisObject;
	}

	/**
	* Build the visible variable map.
	* Need not be synchronized since it cannot be provably stale.
	*/
	private void createVisibleVariables() throws AbsentInformationException {
	if (visibleVariables == null) {
	List<LocalVariable> allVariables = location.method().variables();
	Map<String, LocalVariable> map = new HashMap<String, LocalVariable>(allVariables.size());

	for (LocalVariable variable : allVariables) {
	String name = variable.name();
	if (variable.isVisible(this)) {
	LocalVariable existing = map.get(name);
	if ((existing == null) \|\|
	((LocalVariableImpl)variable).hides(existing)) {
	map.put(name, variable);
	}
	}
	}
	visibleVariables = map;
	}
	}

	/**
	* Return the list of visible variable in the frame.
	* Need not be synchronized since it cannot be provably stale.
	*/
	public List<LocalVariable> visibleVariables() throws AbsentInformationException {
	validateStackFrame();
	createVisibleVariables();
	List<LocalVariable> mapAsList = new ArrayList<LocalVariable>(visibleVariables.values());
	Collections.sort(mapAsList);
	return mapAsList;
	}

	/**
	* Return a particular variable in the frame.
	* Need not be synchronized since it cannot be provably stale.
	*/
	public LocalVariable visibleVariableByName(String name) throws AbsentInformationException {
	validateStackFrame();
	createVisibleVariables();
	return visibleVariables.get(name);
	}

	public Value getValue(LocalVariable variable) {
	List<LocalVariable> list = new ArrayList<LocalVariable>(1);
	list.add(variable);
	return getValues(list).get(variable);
	}

	public Map<LocalVariable, Value> getValues(List<? extends LocalVariable> variables) {
	validateStackFrame();
	validateMirrors(variables);

	int count = variables.size();
	JDWP.StackFrame.GetValues.SlotInfo[] slots =
	new JDWP.StackFrame.GetValues.SlotInfo[count];

	for (int i=0; i<count; ++i) {
	LocalVariableImpl variable = (LocalVariableImpl)variables.get(i);
	if (!variable.isVisible(this)) {
	throw new IllegalArgumentException(variable.name() +
	" is not valid at this frame location");
	}
	slots[i] = new JDWP.StackFrame.GetValues.SlotInfo(variable.slot(),
	(byte)variable.signature().charAt(0));
	}

	PacketStream ps;

	/* protect against defunct frame id */
	synchronized (vm.state()) {
	validateStackFrame();
	ps = JDWP.StackFrame.GetValues.enqueueCommand(vm, thread, id, slots);
	}

	/* actually get it, now that order is guaranteed */
	ValueImpl[] values;
	try {
	values = JDWP.StackFrame.GetValues.waitForReply(vm, ps).values;
	} catch (JDWPException exc) {
	switch (exc.errorCode()) {
	case JDWP.Error.INVALID_FRAMEID:
	case JDWP.Error.THREAD_NOT_SUSPENDED:
	case JDWP.Error.INVALID_THREAD:
	throw new InvalidStackFrameException();
	default:
	throw exc.toJDIException();
	}
	}

	if (count != values.length) {
	throw new InternalException(
	"Wrong number of values returned from target VM");
	}
	Map<LocalVariable, Value> map = new HashMap<LocalVariable, Value>(count);
	for (int i=0; i<count; ++i) {
	LocalVariableImpl variable = (LocalVariableImpl)variables.get(i);
	map.put(variable, values[i]);
	}
	return map;
	}

	public void setValue(LocalVariable variableIntf, Value valueIntf)
	throws InvalidTypeException, ClassNotLoadedException {

	validateStackFrame();
	validateMirror(variableIntf);
	validateMirrorOrNull(valueIntf);

	LocalVariableImpl variable = (LocalVariableImpl)variableIntf;
	ValueImpl value = (ValueImpl)valueIntf;

	if (!variable.isVisible(this)) {
	throw new IllegalArgumentException(variable.name() +
	" is not valid at this frame location");
	}

	try {
	// Validate and convert value if necessary
	value = ValueImpl.prepareForAssignment(value, variable);

	JDWP.StackFrame.SetValues.SlotInfo[] slotVals =
	new JDWP.StackFrame.SetValues.SlotInfo[1];
	slotVals[0] = new JDWP.StackFrame.SetValues.
	SlotInfo(variable.slot(), value);

	PacketStream ps;

	/* protect against defunct frame id */
	synchronized (vm.state()) {
	validateStackFrame();
	ps = JDWP.StackFrame.SetValues.
	enqueueCommand(vm, thread, id, slotVals);
	}

	/* actually set it, now that order is guaranteed */
	try {
	JDWP.StackFrame.SetValues.waitForReply(vm, ps);
	} catch (JDWPException exc) {
	switch (exc.errorCode()) {
	case JDWP.Error.INVALID_FRAMEID:
	case JDWP.Error.THREAD_NOT_SUSPENDED:
	case JDWP.Error.INVALID_THREAD:
	throw new InvalidStackFrameException();
	default:
	throw exc.toJDIException();
	}
	}
	} catch (ClassNotLoadedException e) {
	/*
	* Since we got this exception,
	* the variable type must be a reference type. The value
	* we're trying to set is null, but if the variable's
	* class has not yet been loaded through the enclosing
	* class loader, then setting to null is essentially a
	* no-op, and we should allow it without an exception.
	*/
	if (value != null) {
	throw e;
	}
	}
	}

	public List<Value> getArgumentValues() {
	validateStackFrame();
	MethodImpl mmm = (MethodImpl)location.method();
	List<String> argSigs = mmm.argumentSignatures();
	int count = argSigs.size();
	JDWP.StackFrame.GetValues.SlotInfo[] slots =
	new JDWP.StackFrame.GetValues.SlotInfo[count];

	int slot;
	if (mmm.isStatic()) {
	slot = 0;
	} else {
	slot = 1;
	}
	for (int ii = 0; ii < count; ++ii) {
	char sigChar = argSigs.get(ii).charAt(0);
	slots[ii] = new JDWP.StackFrame.GetValues.SlotInfo(slot++,(byte)sigChar);
	if (sigChar == 'J' \|\| sigChar == 'D') {
	slot++;
	}
	}

	PacketStream ps;

	/* protect against defunct frame id */
	synchronized (vm.state()) {
	validateStackFrame();
	ps = JDWP.StackFrame.GetValues.enqueueCommand(vm, thread, id, slots);
	}

	ValueImpl[] values;
	try {
	values = JDWP.StackFrame.GetValues.waitForReply(vm, ps).values;
	} catch (JDWPException exc) {
	switch (exc.errorCode()) {
	case JDWP.Error.INVALID_FRAMEID:
	case JDWP.Error.THREAD_NOT_SUSPENDED:
	case JDWP.Error.INVALID_THREAD:
	throw new InvalidStackFrameException();
	default:
	throw exc.toJDIException();
	}
	}

	if (count != values.length) {
	throw new InternalException(
	"Wrong number of values returned from target VM");
	}
	return Arrays.asList((Value[])values);
	}

	void pop() throws IncompatibleThreadStateException {
	validateStackFrame();
	// flush caches and disable caching until command completion
	CommandSender sender =
	new CommandSender() {
	public PacketStream send() {
	return JDWP.StackFrame.PopFrames.enqueueCommand(vm,
	thread, id);
	}
	};
	try {
	PacketStream stream = thread.sendResumingCommand(sender);
	JDWP.StackFrame.PopFrames.waitForReply(vm, stream);
	} catch (JDWPException exc) {
	switch (exc.errorCode()) {
	case JDWP.Error.THREAD_NOT_SUSPENDED:
	throw new IncompatibleThreadStateException(
	"Thread not current or suspended");
	case JDWP.Error.INVALID_THREAD: /* zombie */
	throw new IncompatibleThreadStateException("zombie");
	case JDWP.Error.NO_MORE_FRAMES:
	throw new InvalidStackFrameException(
	"No more frames on the stack");
	default:
	throw exc.toJDIException();
	}
	}

	// enable caching - suspended again
	vm.state().freeze();
	}

	public String toString() {
	return location.toString() + " in thread " + thread.toString();
	}
	}