Fix & Continue – Design View

Introduction

There are two new actions added to the debugger core:

• Fix

• Pop Topmost Call,

and one action to JPDA debugger:

• Pop To Here.

Actions Fix and Pop Topmost Call can be used by multiple debugger engines (i.e. there is only one Fix action and one Pop Topmost Call action visible in GUI) but their functionality varies, depending on the current debugging session.

Action Pop To Here is available only in JPDA debugger.

The following classes are added to package org.netbeans.modules.debugger.support.actions:

FixAction
PopTopmostFrame

Two abstract methods are added to class AbstractDebugger:

public abstract void fix()
public abstract void popTopmostFrame()

These actions must be defined by debugger engines. When action FixAction is invoked, method fix() of the current debugging session (Debugger.getCurrentDebugger()) is called. Similarly, when PopTopmostFrame is invoked, method popTopmostFrame() of the current debugging session is called.

State enabled/disabled

Both actions Fix and Pop Topmost Frame are disabled when NetBeans is started. When a session is started or switched, a current debugging session is asked about the actions' state. To allow this, two methods are added to interface org.netbeans.modules.debugger.State:

boolean isFixEnabled()
boolean isPopTopmostFrameEnabled()

When the last session is finished, both actions become disabled.

JPDA Debugger

Each of the above actions (and action Pop To Here) may be unavailable (disabled) during a whole debugging session if:

• JDK used for running NetBeans does not support the action or

• JDK used for running a debuggee does not support the action

JDK used for running NetBeans supports the actions if the following methods are available:

boolean com.sun.jdi.VirtualMachine.redefineClasses(java.util.Map)
boolean com.sun.jdi.ThreadReference.popFrame(com.sun.jdi.StackFrame)

During session startup, JPDA debugger looks up the methods and remembers them if it finds some – the following fields are added to class JPDADebugger:

java.lang.reflect.Method redefineClasses
java.lang.reflect.Method popFrames

If some of the methods is null (i. e. not found), a corresponding action will never be enabled. (These fields are also used for invocation of the methods via reflection.)

JDK used for running a debuggee supports the actions if the following methods return true:

boolean com.sun.jdi.VirtualMachine.canRedefineClasses()
boolean com.sun.jdi.VirtualMachine.canPopFrames()

Summary:

• Action Fix is enabled if all of the following is true:
  – JPDADebugger.redefineClasses != null
  – exactly one node is selected
  – the selected node has a DataObject cookie and the cookie's primary file has MIME-type text/java.

• Action Pop Topmost Call is enabled if all of the following is true:
  – JPDADebugger.popFrames != null
– current thread is suspended
  – current thread has at least two frames
  Its state is updated on the following events:
  – session is switched
  – current session is started/stopped
  – thread is switched
  – current thread is suspended/resumed

• Action Pop To Here is enabled if all of the following is true:
  – JPDADebugger.popFrames != null
  – current thread is suspended
  – the action was invoked on a node that does not represent the most recent call

Implementation

Action Fix

Action Fix is invoked on a (selected) node:

1. If the node has a CompilerCookie, the node is compiled (the process will be almost the same as in method org.netbeans.modules.debugger.support.java.JavaDebugger.compile(DebuggerInfo)).

2. If the compilation fails, an error dialog is displayed and the whole action is aborted.

3. A set of files representing the node is gathered (the node has a DataObject and the DataObject has a set of files – both primary and secondary).

4. If the set of files does not contain any .class file, an error dialog is displayed and the whole action is aborted.

5. For each .class file, a corresponding ReferenceType is requested from the remote JVM and the pair (ReferenceType object, contents of the.class file) is put into a table (java.util.Map). If a ReferenceType object is not found in the JVM for any of the .class files, the class name is remembered (added to a list of unloaded classes). Finally, if all classes were loaded, a JDI command (redefineClasses(Map))is invoked to replace class definition(s). If at least one class were not loaded, a dialog is displayed: The following classes are not loaded in the remote JVM. Do you want to continue? - with options Continue and Cancel. If the user selects Cancel, the whole operation is aborted.

6. If an exception is thrown during call of redefineClasses(Map), an exception dialog is displayed.

Action Pop Topmost Call

1. Simply calls the JDI command:
   1) Get reference to the JDI thread (the current thread).
   2) Pop its topmost frame.

2. If some exception is thrown, displays an error dialog, otherwise updates UI parts of the debugger.

Action Pop To Here

Action Pop To Here is available only from a contextual menu of nodes representing JPDA call stack frames. A new class is added to represent these nodes – JPDACallStackFrameNode:

Method getActions() adds a new action Pop To Here to the default set of actions.

When the action is invoked, it pops the frame (represented by the node) from a call stack (JPDACallStackFrame.threadS).