Dynamic software reconfiguration using control supervisors Ugo Buy 13 June 2005

Background Concurrent, distributed applications are commonplace –Often subject to real-time constraints Possibility of concurrency errors (e.g., mutex violations, deadlocks) and real-time errors (e.g., missed deadlines) Difficult errors to detect through traditional testing –Non-deterministic behavior –Non-repeatable errors Solution: Model relevant aspects of software behavior; analyze with formal methods and simulation

Analysis strategies Formal verification: Automatically check whether a system model satisfies desired concurrency and timing properties –Can exhaustively detect all potential defects –High computational complexity; difficult to scale –Widely explored, mature technologies –Applied to real-world design problems (both hardware and software) with increasing frequency –Typically work on finite state automata or Petri nets

Analysis strategies Supervisory control of discrete event systems Given system model, add controller enforcing desired concurrency and timing properties to model –Often more tractable than verification –Support dynamic reconfiguration through automatic supervisor synthesis –Similar models to verification (e.g., finite state automata and Petri nets)

Current project Dynamic reconfiguration of discrete manufacturing systems Funding from NIST in collaboration with Starthis, Inc. Rationale: –Control programs are hard to write and maintain –Flexible manufacturing demands rapid reconfiguration –Possibility of deadlock, mutex violations, deadline violations in manufacturing plants –Disastrous consequences sometimes possible

Approach Avoid verification complexity with supervisory control Petri nets vs. finite state automata Synthesis of deadline-enforcing supervisors using net unfolding Compositional methods (e.g., hierarchical control)

Flow of supervisory synthesis GUI Translator Supervisor generator SFCs Plant spec ConstraintsTPNs Refined TPNs Code generator Control code 1.Specify plant behavior and correctness properties 2.Generate Petri net 3.Synthesize control supervisor 4.Generate target code

Achievements to date System for enforcing deadlines on transition firing in time Petri nets Integration of methods for enforcing mutual exclusion and freedom from deadlock Framework for compositional analysis (hierarchical control)

Additional research Decision support for emergency response during mass casualty situations –Collaboration with Prof. Houshang Darabi and his group in Industrial Engineering –Model healthcare, transportation and communication systems needed for emergency response –Work local government agencies involved in emergency response

Potential collaborations Strong software engineering group at UIC –Tadao Murata –Sol Shatz –Jeffrey Tsai –Prasad Sistla –Lenore Zuck Additional strengths in computer security, transportation systems