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Snap-Stabilizing Committee Coordination

Snap-Stabilizing Committee Coordination. Borzoo Bonakdarpour , Stéphane Devismes , and Frank Petit. Committee Coordination. Committee Coordination. Wait. Wait. Wait. Synchronization. Wait. Committee Coordination. Exclusion. Committee Coordination. Wait. Wait. Wait. Progress.

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Snap-Stabilizing Committee Coordination

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  1. Snap-Stabilizing Committee Coordination BorzooBonakdarpour, Stéphane Devismes, and Frank Petit

  2. Committee Coordination Cap Estérel, mardi 24 mai 2011, ALGOTEL'2011

  3. Committee Coordination Wait Wait Wait Synchronization Wait Cap Estérel, mardi 24 mai 2011, ALGOTEL'2011

  4. Committee Coordination Exclusion Cap Estérel, mardi 24 mai 2011, ALGOTEL'2011

  5. Committee Coordination Wait Wait Wait Progress Cap Estérel, mardi 24 mai 2011, ALGOTEL'2011

  6. Snap-Stabilization Cap Estérel, mardi 24 mai 2011, ALGOTEL'2011

  7. Related property: Self-Stabilization Cap Estérel, mardi 24 mai 2011, ALGOTEL'2011

  8. Other properties • Maximal Concurrency • Fairness • 2-phase discussion time Cap Estérel, mardi 24 mai 2011, ALGOTEL'2011

  9. Maximal Concurrency Wait Wait Wait Wait Wait Cap Estérel, mardi 24 mai 2011, ALGOTEL'2011

  10. (Professor) Fairness Fairness Every professor eventually participates in a committee meeting that it is a member of. • Assumption • (otherwise, impossible[2]) Every professor wants to participate in a committee meeting infinitely often. [2] Y.-K. Tsay and R. Bagrodia. Some impossibility results in interprocesssynchronization. Distributed Computing, 6(4):221–231, 1993. IEEE International Parallel and Distributed Processing Symposium (IPDPS'11)

  11. Impossibility of Fairness and Maximal Concurrency We design an algorithm for each property Wait Wait Wait Wait Wait Cap Estérel, mardi 24 mai 2011, ALGOTEL'2011

  12. 2-Phase Discussion Time • Before: atomic event assumption • All members start and finished the meeting simultaneously • 2-Phase discussion: • Phase 1 (essential discussion) : all participants must discuss • Phase 2 (voluntary discussion) : participants discuss freely • The meeting ends when any participant decide to leave the meeting Cap Estérel, mardi 24 mai 2011, ALGOTEL'2011

  13. Algorithms • Snap-stabilizing 2-Phase Committee Coordination with Maximal Concurrency • Snap-stabilizing 2-Phase Fair Committee Coordination Cap Estérel, mardi 24 mai 2011, ALGOTEL'2011

  14. Snap-stabilizing 2-Phase Committee Coordination with Maximal Concurrency Step 1: Looking for a committee to participate L L L L L L L Cap Estérel, mardi 24 mai 2011, ALGOTEL'2011

  15. Snap-stabilizing 2-Phase Committee Coordination with Maximal Concurrency Step 2: Choosing a committee where all members are also looking L L L L L L L Cap Estérel, mardi 24 mai 2011, ALGOTEL'2011

  16. Snap-stabilizing 2-Phase Committee Coordination with Maximal Concurrency Step 3: Getting ready to participate in a meeting L Ok L Ok L L Ok L L Ok L Cap Estérel, mardi 24 mai 2011, ALGOTEL'2011

  17. Snap-stabilizing 2-Phase Committee Coordination with Maximal Concurrency Step 4: Committee meeting convenes Ok Ok L L Ok Ok L Cap Estérel, mardi 24 mai 2011, ALGOTEL'2011

  18. Snap-stabilizing 2-Phase Committee Coordination with Maximal Concurrency Step 5: After essential discussion, professors leave the meeting Ok D Ok D L L Ok D Ok D L Cap Estérel, mardi 24 mai 2011, ALGOTEL'2011 18

  19. Snap-stabilizing 2-Phase Fair CCSelection of the committee: ID ? 2 6 5 L D Ok Ok D L 3 4 7 L D L 1 Ok L Ok D L Cap Estérel, mardi 24 mai 2011, ALGOTEL'2011

  20. Snap-stabilizing 2-Phase Fair CCSelection of the committee: Token-Based Priority (1/2) • Let P, Q be processes • If P hold a token, but not Q, then • P has a higher than Q • Otherwise • Priorities are given by the IDs Cap Estérel, mardi 24 mai 2011, ALGOTEL'2011

  21. Snap-stabilizing 2-Phase Fair CCSelection of the committee: Token-Based Priority (1/2) 2 6 T 5 L D Ok Ok D L 3 4 7 L T D L L 1 Ok L Ok D Cap Estérel, mardi 24 mai 2011, ALGOTEL'2011

  22. When release the token ? 2 6 5 If the token holder has no guarantee to eventually convene a meeting, it releases the token L L 3 4 7 L T L 1 L Cap Estérel, mardi 24 mai 2011, ALGOTEL'2011

  23. Snap-stabilizing 2-Phase Fair Committee Coordination • Recall: Every professor wants to participate in a committee meeting infinitely often. (required assumption) • Mainly differ by the way the token is handled: • The token holder only releases the token at the end a meeting Cap Estérel, mardi 24 mai 2011, ALGOTEL'2011

  24. Locked Professors 6 5 2 Ok L L Locked T L 3 4 1 L Ok Cap Estérel, mardi 24 mai 2011, ALGOTEL'2011

  25. Concurrency: Algo 1 vs.Algo 2 • Algo 1: Maximal matching • Algo 2: almost… 5 2 Ok Locked L L T 4 3 L 1 Ok Cap Estérel, mardi 24 mai 2011, ALGOTEL'2011

  26. Conclusion • Summary • Weconsidered the distributedcommittee coordination problem • Weshowedthatsatisfyingfairnessandmaximal concurrencyisimpossibleeven if professorsdesire to participate in meetings infinitelyoften • Weproposed a snap-stabilizingalgorithms for eachconflictingproperty. • Future work • Dynamic join / leave of professor • Priorities on committee Cap Estérel, mardi 24 mai 2011, ALGOTEL'2011

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