3 Debugger

The user interface is divided in two integrated parts: the source browser, and the Valhalla Universe. The source browser enables browsing in the source code of the application being debugged (as well as other source files), and the Valhalla Universe enables the display of runtime objects and execution stacks of the actual execution during the execution of the application.

Figure 2: Debugger universe

The program execution may be controlled e.g. by setting breakpoints and single stepping at the BETA source level. Runtime errors are caught by Valhalla that will display the offending object and code. From there, program state can be browsed to locate the cause of error. The debugged program executes in a process of its own, being watched by Valhalla, but otherwise unaffected.

Using the Mjølner Debugger you may:

• Control and trace the execution of a BETA program by setting breakpoints and stepping at the level of single BETA source lines, stepping over procedure-calls and even single step at the level of machine code instructions.
• Simultaneously examine the state of any number of objects.
• Examine the execution stack and view code and objects on the stack.
• Examine the program heaps and view objects on the heaps.
• Simultaneously view any number of windows containing source code.

Figure 3: A breakpoint

Trace points

In order to make it easy to trace the execution of the application, Valhalla offers trace points. A trace point is a point in the source code, with an associated text string. Each time the execution passes a trace point, the text string is printed on the standard output. The text string is specified as part of the specification of the trace point.

Break points

In order to inspect the state of objects during the execution of the application, Valhalla offers break points. A break point is a point in the source code. Each time the execution passes a break point, control is passed back to Valhalla, enabling you to inspect the state of the execution, the state of runtime objects, etc.

Execution Control

Using Valhalla, you can control the execution of any BETA application. You can start and stop the execution, set break points and trace points, single step at the level of machine code instructions, at the level of BETA imperatives, step over procedure calls, etc.

Runtime Inspection

Valhalla offers extensive support for inspection of the runtime structure of the running application. You can examine the state of objects and runtime stacks. Using the easy-to-use graphical interface, you can navigate through the entire object structure, and locate any object in the application, inspecting its state.