1. Hints for Building Self-. Systems Vijay K
Hints for Building Self-* Systems Vijay K. Garg The University of Texas at Austin Austin, TX

2. Talk Outline Overview Hints for Self-* Systems Paradise
Specify: Know your goals
Observe: Know your state
Keep choices: Know multiple ways
Plan: Know your strategy
Control: reconfigure, reset, reorganize, adapt
Paradise

3. Specify: Know your goals
Biological Systems: goals at multiple levels
Survival, happiness, money, job
Computer Systems are not aware of their goals
At best, we have specs of the programs
Need
Specs at multiple levels
Using Specs for Runtime Verification
Adapting to the environment

4. Observe: Know your state
Self-awareness: is the state consistent with goals?
Monitoring for system properties
Stable Properties e.g. [Chandy,Lamport 85]
Unstable Properties
Single State based e.g. Linear Predicates [Chase, Garg 95], Relational Predicates [Tomlinson, Garg 96]
Temporal Logic based e.g. Regular CTL [Sen, Garg 04]
Need:
Integration with runtime environments

5. Choices: Know multiple ways
Determinism considered dangerous
Nondeterminism allows the system to deal with
Faults
Uncertainty
Changing environment
Need
Nondeterministic choice in general prog. Languages (e.g. Dijkstra’s Guarded Command Language)
Support for selective communication (e.g. CSP)
Support for family of modules

6. Plan: Know your strategy
Know your state space
Exploit what computers are good at
View program as two parts
Finite state part: computer analyzable
Infinite part: trust humans
Lookahead Execution
Computation slicing [Garg, Mittal 2001]
Need
Support for systems with lookahead
Support for on-the-fly model checking

7. Control: Controlled Execution
Use nondeterminism to your advantage
Try different order of message processing
Impose additional synchronization [Tarafdar, Garg 04]
Supervisory Control of Discrete Event Systems [Ramadge and Wonham 89, Kumar and Garg 95]
Tunable parameters (adaptive control)
Need
execution environments with control
Programming languages that support feedback

8. Paradise Project Key Abstraction: Global Properties
Model Checking and Verification: Check global properties against model of the program (Promela)
Simulation and Debugging: Global breakpoints, Trace analysis
Fault-Tolerance: Monitoring for global properties, Controlled Re-execution
methodology => fusion of some of the best ideas from the digital hardware and software engineering worlds
Development => model-centric
System model => executable
Monitoring for global properties => Online property checking

9. Paradise Environment
Predicate
Slicer
Observe
Program
Monitor
Control

10. Paradise Tools
Trace Cover SPIN (Model Checker): alleviating state explosion
Visual Dashboard
Partial Order Trace Analysis (POTA): slicing
Paradise Library: tracking dependency, global snapshot, global properties
Paradise Execution Engine: control

11. Conclusions
Current execution engines are too primitive to build self-* systems
Need more knowledge
Goals, multiple choices, current state
Research at PDSLAB
Restricted predicates ?