1. DOLCLAN Middleware Support for Peer-to-Peer Distributed Shared Objects Jakob E. Bardram and Martin Mogensen University of Aarhus, Denmark [Center for Pervasive Healthcare] http://pervasivehealthcare.com

2. DAIS '07DOLCLAN - Middleware Support for Peer-to-Peer Distributed Shared Objects2 Background Motivation –Pervasive Computing –Mobility, pervasiveness, changing environments, … –Transient infrastructure –Heterogeneous devices, incl. Sensors –Increasing demand for dependability of such systems –Termed by Laprie [1] as the "dependability gap" Goal –Pervasive Computing infrastructure –Development framework –Integrated language support [1] Jean-Claude Laprie Resilience for the Scalability of Dependability In: Proceedings of the IEEE International Symposium on Network Computing and Applications

3. DAIS '07DOLCLAN - Middleware Support for Peer-to-Peer Distributed Shared Objects3 Main Problem RPC Paradigm –Remote objects accessed by procedure calls –Assumes reliable infrastructure –Assumes stable host machine –Synchronous blocking procedure calls Pervasive Environments –Intermitted network connections –Heterogeneous devices –More or less (un)stable devices => RPC does not fit in this environment !

4. DAIS '07DOLCLAN - Middleware Support for Peer-to-Peer Distributed Shared Objects4 Approach Peer-to-Peer Distributed Shared Objects –Physically distributed replicas –Peer-to-Peer updates Advantages –Heightens application responsiveness –Support disconnected work –Distributes computational and network load –Resilient network joining Drawbacks –Increased complexity managing data –Increased complexity managing network topology –DOLCLAN handles these

5. DAIS '07DOLCLAN - Middleware Support for Peer-to-Peer Distributed Shared Objects5 Concept PDSO Peer-to-Peer Distributed Shared Objects –Physical distribution –Synchronized objects –Peer-to-Peer updates –Responsive optimistic concurrency protocol –Distribution-aware programming

6. DAIS '07DOLCLAN - Middleware Support for Peer-to-Peer Distributed Shared Objects6 Concept PDSO

7. DAIS '07DOLCLAN - Middleware Support for Peer-to-Peer Distributed Shared Objects7 Terms PDSO Terms used –OID : Object Identifier Names a single local replica E.g. A –PDSO : Peer-to-Peer Distributed Shared Object Set of local replicas named by the same OID E.g. PDSO(A) –Group : Set of PDSOs Defined by the transitive closure of a specified PDSO I.e. There is a path in the object graph E.g. Group(PDSO(A))

8. DAIS '07DOLCLAN - Middleware Support for Peer-to-Peer Distributed Shared Objects8 Concept PDSO

9. DAIS '07DOLCLAN - Middleware Support for Peer-to-Peer Distributed Shared Objects9 Distribution Awareness Key differentiation between what we [2] have termed –accountable events Crucial events, long lived Affects the state of the system in long time The system needs to account for the events TCP or reliable multicast –ephemeral events Transient events, short lived Collaboration awareness events Tele-pointers, voice links, etc... UDP or unreliable multicast [2] Bardram, J.E., Bunde-Pedersen, J., Mogensen, M.: Differentiating between Accountable and Ephemeral Events in the ABC Hybrid Architecture for Activity-Based Collaboration. In: Proceedings of the IEEE International Conference on Collaborative Computing 2005

10. DAIS '07DOLCLAN - Middleware Support for Peer-to-Peer Distributed Shared Objects10 DOLCLAN Proof-of-PDSO-concept implemented –Service discovery –Peer joining –Synchronous object state replication –Data management –Network management –Language support

11. DAIS '07DOLCLAN - Middleware Support for Peer-to-Peer Distributed Shared Objects11 A simple example Let’s create a distributed Pacman game

12. DAIS '07DOLCLAN - Middleware Support for Peer-to-Peer Distributed Shared Objects12 A simple example A model for a distributed Pacman game

13. DAIS '07DOLCLAN - Middleware Support for Peer-to-Peer Distributed Shared Objects13 C# Language Support New keywords distributed classes and fields accountable and ephemeral modifiers

14. DAIS '07DOLCLAN - Middleware Support for Peer-to-Peer Distributed Shared Objects14 C# Language Support New keywords distributed properties accountable and ephemeral modifiers

15. DAIS '07DOLCLAN - Middleware Support for Peer-to-Peer Distributed Shared Objects15 C# Language Support Object creation and joining Create PDSOs with the new keyword Join PDSO groups with the join keyword

16. DAIS '07DOLCLAN - Middleware Support for Peer-to-Peer Distributed Shared Objects16 C# Language Support Domain specific conflict resolution Override public void merge(object)

17. DAIS '07DOLCLAN - Middleware Support for Peer-to-Peer Distributed Shared Objects17 C# Language Support The complete EaterModel You are not supposed to read this ;-)

18. DAIS '07DOLCLAN - Middleware Support for Peer-to-Peer Distributed Shared Objects18 Evaluation - Language Support A simple programming task Create a distributed tree-view application

19. DAIS '07DOLCLAN - Middleware Support for Peer-to-Peer Distributed Shared Objects19 Evaluation - Performance Time to push state changes into the net Does not say anything about time to deliver Stresses the need for ephemeral and accountable modifiers

20. DAIS '07DOLCLAN - Middleware Support for Peer-to-Peer Distributed Shared Objects20 Evaluation - Utility Can pervasive applications be created? –We have used DOLCLAN for the ABC framework –Adds support for ad-hoc collaboration –Re-coding took few days –Shows that more complex applications can be created

21. DAIS '07DOLCLAN - Middleware Support for Peer-to-Peer Distributed Shared Objects21 On-going Work Technical work –Support outside LANs –Support for sensor networks –.NET Compact Framework library Applications –Integration with real EHR (Electronic Health Record) –Enable collaborative sessions (Between surgeons in the operating theater and second level experts) –Integration with PACS system (Picture, Archiving, and Communication System) Deployment –Horsens hospital, Denmark –Surgical department

22. DAIS '07DOLCLAN - Middleware Support for Peer-to-Peer Distributed Shared Objects22 Summary Challenges –RPC paradigm is imperfect in a pervasive environment Peer-to-Peer Distributed Shared Objects –Pervasive Computing infrastructure –Development framework –Integrated language support On-going work –Extending support and infrastructure –Creating pervasive applications –Deploying applications in hospitals

23. DAIS '07DOLCLAN - Middleware Support for Peer-to-Peer Distributed Shared Objects23 More Information [Martin Mogensen - spider@daimi.au.dk] Thank you for listening ! [Center for Pervasive Healthcare] www.pervasivehealthcare.com [iHospital research project at Horsens Hospital, Denmark] www.ihospital.dk [Activity Based Computing and the ABC framework] www.activity-based-computing.org