Steering and its prototype implementation

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Steeringandits prototype implementation
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The concept of steering

• Monitoring allows the user to have precise
  information about the behavior of the running
  system and detect requirement violations as soon
  as possible
• In addition, this information can be used to
  diagnose the problem and suggest a remedy
• Steering provides feedback into the system,
  allowing the user to utilize this information to
  correct the system behavior

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Steering actions

• The runtime checker performs steering by invoking
  a steering action, which is executed within the
  system
• The purpose of a steering action is to restore
  the system to a good state

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Requirements for steering

• Steering must be conservative
• unless a steering action is invoked, there is no
  effect on the system
• Steering must be effective
• each steering action has an effect on the
  systems behavior

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Steering Scripts

• Steering is described using a script
• The script defines
• objects of the system affected by steering
• actions performed when steering is invoked
• It may be unsafe to execute an action at an
  arbitrary point. The steering script must give
  information about the placement of steering
  actions

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Placement of steering actions

• The invocation of a steering action is delayed
  until a condition associated with the action is
  satisfied
• Steering conditions delegate the problem of
  effectiveness to the user
• Dynamic vs. static conditions
• dynamic conditions depend on run-time state of
  the system
• may allow more precise placement

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Dynamic vs. static conditions

• Dynamic conditions
• depend on run-time state of the system
• may allow more precise placement
• require more evaluation effort may compromise
  conservativeness
• Static conditions
• statically identify a safe region in the code
• easy to check

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Steering Action Definition Language (SADL)
steering script mav steered objects Air
MAVair java.awt.geom.Point2D
MAVposition steering action collapse
call (MAVair).setRepulse(false) after write
MAVposition end
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Prototype implementation of steering

• The existing MaC prototype is extended to
  incorporate steering
• instrumentation adds code to test for a steering
  action and to execute it if necessary at the
  specified placement locations
• an Injector class is added to the system to
  communicate with the checker and accept action
  invocations
• MEDL is extended to include action invocations in
  response to events

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MaC Prototype with steering
Program (Java byte code)
Monitoring Script (PEDL)
Steering Script (SADL)
Requirements (MEDL)
SADL Compiler
MEDL Compiler
PEDL Compiler
Instrumentation Information
Filter Generator (JTREK)
Compiled MEDL
Compiled PEDL
Instrumented
Code
Event Recognizer
Checker