Snap-Stabilizing Committee Coordination Borzoo Bonakdarpour, Stéphane Devismes, and Frank Petit

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

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

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

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

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

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

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

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

(Professor) Fairness May 17, 2011 IEEE International Parallel and Distributed Processing Symposium (IPDPS'11) Every professor eventually participates in a committee meeting that it is a member of. Assumption [2]) (otherwise, impossible [2]) Fairness [2] Y.-K. Tsay and R. Bagrodia. Some impossibility results in interprocess synchronization. Distributed Computing, 6(4):221–231, Every professor wants to participate in a committee meeting infinitely often.

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

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'

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

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

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

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

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

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

Snap-stabilizing 2-Phase Fair CC Selection of the committee: ID ? Cap Estérel, mardi 24 mai 2011, ALGOTEL' L L L L L L OkD D D D

Snap-stabilizing 2-Phase Fair CC Selection 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'

Snap-stabilizing 2-Phase Fair CC Selection of the committee: Token-Based Priority (1/2) Cap Estérel, mardi 24 mai 2011, ALGOTEL' L L L L L OkD D D D T T L

When release the token ? Cap Estérel, mardi 24 mai 2011, ALGOTEL' L L L L L T If the token holder has no guarantee to eventually convene a meeting, it releases the token

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'

Locked Professors Cap Estérel, mardi 24 mai 2011, ALGOTEL' L L L Ok L T Locked

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

Conclusion Summary – We considered the distributed committee coordination problem – We showed that satisfying fairness and maximal concurrency is impossible even if professors desire to participate in meetings infinitely often – We proposed a snap-stabilizing algorithms for each conflicting property. Future work – Dynamic join / leave of professor – Priorities on committee Cap Estérel, mardi 24 mai 2011, ALGOTEL'