Component Composition for Embedded Systems Using Semantic Aspect-Oriented Programming

1. Component Composition for Embedded Systems Using Semantic Aspect-Oriented Programming Martin Rinard Laboratory for Computer Science Massachusetts Institute of Technology F33615-00-C-1692

2. Problem Description How can we improve flexibility, reliability, and predictability of software for embedded and real-time systems? • Need for better support for distributed computations • Need to easily compose components on different platforms • Need for implementations that survive partial failures • Need for better understanding of distributed implementations • Understand communication patterns and their implications • Support for fault propagation analysis • Exploit information to transform software • Lack of real-time support in standard languages and systems • Lack of real-time memory management support in Java • Lack of real-time scheduling support in Java

3. Objective Technical Approach Role Analysis • Capture changing roles objects play in computation • Points-to relationships determine roles • Role Specifications • Programmer supplied • Dynamically discovered • Statically verified Transformations • Specialized communication • Point-to-point • Targeted multicast • Request/response • Preemptively move or replicate objects to close windows of vulnerability Interaction Analysis • Match role changes with component movements • Match publishers and subscribers • Compute failure propagation information Support for Distributed Real-Time Systems Shared Object Communication • Shared reference system • Thread-based failure model Distributed Interaction System Event Notification • Publish/Subscribe Primitives Predictable Memory Management • Region-Based allocation primitives • Pointer and escape analysis • Validates correct region use • Eliminates dynamic checks • Role analysis enables safe explicit memory deallocation Real-Time Scheduling • Compiler-controlled scheduling • Preemptive thread scheduling • Asynchronous event dispatch Real Time Java

4. System Architecture Shared Object Space Shared Event Space Subscribe Publish Distributed RTJ Components

5. Objectives for Distributed Components • Understand how components interact • Event notification relationships • Communication patterns • Failure propagation • Replace pub/sub with specialized mechanisms • Point-to-point communication • Multicast communication • Request/response communication • Preemptively move or replicate objects to close windows of vulnerability to failures

6. Technical Approach Observations • Objects play different roles in computation • Role is conceptually similar to type • Capture important differences between objects • Useful constraints associated with roles (can’t apply stop operation to stationary tank) Stationary Tank Moving Tank Disabled Tank Roles

7. Technical Approach Observations • Role of object may change during computation • Even though identity stays the same Stationary Tank Moving Tank Disabled Tank Roles Role Transitions

8. Technical Approach Observations • In a standard type system • Object’s type corresponds to its class • Object’s class does not change • Type system does not capture object’s roles Tank Class Stationary Tank Moving Tank Disabled Tank Roles Role Transitions

9. Technical Approach Goal • Develop a formalism (role types) to capture changing roles that objects play in computation • Statically verify role constraints and transitions Tank Class Stationary Tank Moving Tank Disabled Tank Roles Role Transitions

10. Role Transitions StationaryTankList MovingTankList DisabledTankList

11. Role Transitions StationaryTankList MovingTankList DisabledTankList

12. Role Transitions StationaryTankList MovingTankList DisabledTankList

13. Role Classification • Relative Classification • Role determined by data structure membership • Role changes correspond to movements between data structures • Role depends on points-to relationships • Content-based Classification • Role determined by values of object’s fields • Role changes correspond to field assignments • History-based Classification • Role determined by operations applied to object • Role changes correspond to method executions

14. Relative Role View of Objects For Each Role • Set of incoming slots • Reference that fills each slot (role.field) Stationary Tank List Node Stationary Tank String Tank Model next Integer Top Speed item Current Speed Moving Tank List Node Moving Tank String Stationary Tank Role • One incoming slot • Filled by Stationary Tank List Node.item Reference Tank Model next Integer Top Speed item Current Speed Integer Moving Tank Role • One incoming slot • Filled by Moving Tank List Node.item Reference

15. Role Analysis • Role information at method boundaries • Programmer provided or • Dynamically discovered • Statically verified using generalized interprocedural shape analysis

16. Applications of Roles • Roles provide object referencing relationships • Object referencing determines interaction patterns • Interaction analysis leverages roles to statically extract interaction patterns • Match publishers with subscribers • Match role changes with movements of objects between components • Compute failure propagation information • Move or replicate objects to eliminate windows of failure vulnerability

17. More Benefits of Roles • Software Engineering Benefits • Enhanced implementation transparency • Role constraints = safety checks that take application semantics into account • Safe explicit memory deallocation

18. Real-Time Java

19. Real-Time Java Memory Management • Scoped Memories for Real-Time Memory Management • Implementation in MIT Flex System • Pointer and Escape Analysis • Verifies correct use of scoped memories • Eliminates dynamic scoped memory checks • Analysis of Multithreaded Programs (PPoPP ’01) • Computes interactions between threads • Capture objects accessed by multiple threads • Incrementalized Analysis (PLDI ’01)

20. Real-Time Java Scheduling Compiler-controlled scheduling • Start with lightweight user-level threads package • Compile scheduling checks into generated code • Check for: • Asynchronous event dispatch • Preemptive thread switch • Result: • Scheduler part of Java Run-Time (at user level) • Can be partially generated by compiler • Minimal demands on OS • Maximum flexibility in implementation

21. Contribution to PCES Goals What we provide: Automated understanding of distributed, embedded, and real-time software • Analyses • Pointer and escape analysis • Role analysis • Interaction analysis • Some envisioned uses: • Safe memory management alternatives for Real-Time Java • Verification of safe use of region-based allocation • Roles enable explicit deallocation instead of garbage collection • Interaction analysis • Understanding and validation of synchronization interactions • Understanding of communication patterns • Understanding of how failures propagate • Validations of ABSENCE of interactions • Transformations • Specialized, efficient communication implementations • Close windows of failure vulnerability

22. Contribution to Military Applications Basic Contribution: More Flexible, Reliable, Predictable Real-Time, Distributed, and Embedded Systems • Implementation technology to enable use of standard, widely used language (Java) in military applications • Compiler-controlled event and thread management • Memory management algorithms for real-time systems • Analyses and transformations for understanding and improving military software systems • Potential application areas • Real-time monitoring and control • Information collection and presentation • Integrating (distributed) systems of systems

23. Project Tasks and Schedule • Real-Time Java Implementation • Scoped Memories (Year 1) • Thread and Event Scheduling (Year 3) • Publish/Subscribe Implementation • Initial prototype (Year 2) • Final version (Year 4) • Pointer and Escape Analysis (Year 1) • Role Analysis • Initial design and implementation (Year 2.5) • Final design and implementation (Year 4) • Interaction Analysis and Transformations • Failure propagation analysis (Year 3) • Transformations to close windows of failurevulnerability (Year 4)

24. Technical Progress/Accomplishments • Implementation of Real-Time Java Scoped Memories • Scoped memory allocation primitives • Pointer and escape analysis for multithreaded programs (PPoPP ’01) • Verify correct use of scoped allocation • Eliminate dynamic checks • Incrementalized pointer and escape analysis (PLDI ’01) • Initial phases of distributed surveillance application • Initial JavaCar prototype – 1/6 scale car with • 233 MHz StrongARM, 32 Mbytes, running Java on Linux • Camera, wireless ethernet, USB, various sensors • Speed and steering control • Initial role design, specification language, analysis

25. Next Milestones Progress in Following Areas • Publish/Subscribe Design and Implementation • Realization in Java (Event class) • Event distribution mechanism • Shared object space mechanism • Real-Time Java Threads and Events • Role Design, Specification, and Analysis • JavaCar and Surveillance Applications

26. Collaborations • Washington University • Real-Time Java Memory Management • Dynamic Scope Generation (Washington) • Static Scope Verification (MIT) • Real-Time Event Service • Stanford, Kansas State University (Model Extraction) • Purdue, SUNY Oswego, Maryland (RT Java) • Utah (Analysis for Component Constraints) • Anyone else with Real-Time Java needs • We provide prototype open implementation • We provide analysis prototypes

27. Technology Transfer • Illustrations of Implementation Techniques for Real-Time Java • Implementation available under GNU GPL • Anyone can download it, use it, improve it • http://www.cag.lcs.mit.edu/~rinard/pces • Real-Time Java as Infection Vector • Integrated pointer and escape analysis • Correctness tool for region allocation • Enables stack allocation (reduces memory footprint) • Integrated role discovery and analysis • Dynamic discovery leads to easy initial experience • Roles become central abstraction for developer • Roles + publish/subscribe system = easy, effective distribution • Communication and failure propagation analysis • Useful transformations • Dynamic deployment • Our system serves as prototype • Illustrates key implementation techniques • Helps others evaluate suitability for their application

28. Program Issues

29. Example Roles Stationary Tank List Node Tank Object String Tank Model next Top Speed Integer item Current Speed

30. Moving Tank List Node Tank Object String Tank Model next Top Speed Integer item Current Speed Integer

31. Standard View of Object Incoming References Outgoing References Tank Object String Tank Model • Top Speed Integer • Current Speed • Integer Fields

32. Incrementalized Analysis Big Program

33. Incrementalized Analysis Object Allocation Sites to Capture

34. Incrementalized Analysis Standard Approach: Analyze Entire Program

35. Incrementalized Analysis Our Approach: Incrementally Analyze Region Surrounding Each Allocation Site

36. Incrementalized Analysis Our Approach: Incrementally Analyze Region Surrounding Each Allocation Site

37. Incrementalized Analysis Our Approach: Incrementally Analyze Region Surrounding Each Allocation Site

38. Incrementalized Analysis • Key Question: Where to invest analysis resources? • Obtain estimates of • Payoff of capturing allocation site • Likelihood of capturing site • If can capture site, cost of the capture • As invest resources in site, improve estimates • Invest resources in site with (current) best estimated return on invested resources • Results show can obtain almost all benefit of whole-program analysis at fraction of cost (PLDI ’01)