Logging Messages and Debugging Delegates

Overview

As when writing any custom code, when writing your delegates you will likely want to have them log messages and to debug them in your Integrated Development Environment (IDE). Behavior Execution Engine makes both of these tasks more convenient by providing a built-in simulation logger. In this section, you will debug an exception using log messages.

This section covers the following concepts:

• The Behavior Execution Engine SimulationLogger

mSimulationLogger.info("currentPowerDraw=" + currentPowerDrawProperty.getValue());
mSimulationLogger.info("powerRequest=" + powerRequestProperty.getValue());
mSimulationLogger.info("maxPowerDraw=" + maxPowerDrawProperty.getValue());

Figure A1: Logging property values in a delegate

Prerequisites

Instructions

Examine the error log

1. Open the UAVMission.mdzip project from the previous section.
2. Execute the simulation and observe that the simulation fails with the following exception:

   ERROR: java.lang.Exception:
   com.agi.moxie.uml.infrastructure.expressions.JexlExpressionParser.parseBooleanExpression:35
   variable 'powerRequest' is undefined within guard source text:
   currentPowerDraw + powerRequest < maxPowerDraw

   This indicates that the powerRequest property used in the currentPowerDraw + powerRequest < maxPowerDraw guard is null when the guard is evaluated.

Log the property values

After you include the SimulationLogger dependency from the analysis tool controller in your delegates, you can use it to log messages to the simulation log file and console.

1. In the state history trace for the PowerSystem State Machine, notice that the providePower() operation executes immediately before the guard that is throwing the exception. Unlike the guard, this operation has corresponding delegate code in which you can log the values of the properties used in the guard.
2. In the PowerSystemDelegate class, add the following import statement:

   import com.agi.moxie.api.SimulationLogger;

3. Add the following private field:

   private SimulationLogger mSimulationLogger;

4. Add the following dependency injection and field initialization in the constructor:

   public PowerSystemDelegate( ...
           @InjectByName("simulationLogger") SimulationLogger simulationLogger,
            ... ) {
       mSimulationLogger = simulationLogger;
        ...
   }

5. Add the following logging statements for the SysML property values in the providePower() method:

   mSimulationLogger.info("currentPowerDraw=" + currentPowerDrawProperty.getValue());
   mSimulationLogger.info("powerRequest=" + powerRequestProperty.getValue());
   mSimulationLogger.info("maxPowerDraw=" + maxPowerDrawProperty.getValue());

6. Save your work and reinstall the delegate module.
7. Execute the simulation again and observe that the simulation now reports the following information before the exception:

   INFO: currentPowerDraw=3.0
   INFO: powerRequest=null
   INFO: maxPowerDraw=100.0

Set the null property value

In the SysML model, the computer requests that the power system providePower() for specific subsystems, so the power system should store the value that the computer requests in the powerRequest property.

1. Add the following code before the logging statements in the providePower() method to set the property:

   powerRequestProperty.setValue(request);

2. Save your work and reinstall the delegate module.
3. Execute the simulation again and observe that the simulation no longer throws the exception for null operands in the guard and that it completes successfully.

Debugging State Machines

Regardless of whether the "Debug Mode" is active, the SysML Client also supports setting breakpoints inside the SysML state machines to pause execution. When using STK, this allows you to pause execution to run additional reports, graphs, and perform ad-hoc analysis to diagnose potential issues occurring at specific moments in the flow of SysML behaviors.

Figure A2: Color Legend for debugging SysML state machines

For more details, see the section on debugging in the Debugging with State Machines overview.