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## Laws of Order: Expensive Synchronization in Concurrent Algorithms Cannot be

Circleville Bible College, US has reference to this Academic Journal, Laws of Order: Expensive Synchronization in Concurrent Algorithms Cannot be Eliminated1 Martin Vechev IBM T.J. Watson Research Center Joint work with: Hagit Attiya, Rachid Guerraoui, Danny Hendler, Petr Kuznetsov, Maged Michael Concurrency2?is about synchronization Synchronization3but how much ?

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Synchronization4we don?t know Synchronization5manual empirical process Synchronization6time consuming

Synchronization7too much is inefficient Synchronization8too little is incorrect Example: Set ADT9bool add(int key){ ???}bool remove(int key){ ???}bool contains(int key){ ???}

14: Intro so that Routing Algorithms Routing Routing Roadmap Global Dynamic Routing Link State Algorithm: Some Notation Preventing Oscillations

Our Result10Concurrent abstract data types (stacks, queues, sets, hash tables, counters ?)and mutual exclusion algorithms must use expensive synchronization Implications11concurrent programming: guidance on when avoiding expensive synchronization is futile12??although I hope that these shortcomings will be addressed, I hasten so that add that they are insignificant compared so that the huge step forward that this paper represents?.? Linux Weekly News, Jan 26, 2011 lwn /Articles/423994/ Implications

Implications13hardware design: motivation so that lower cost of specific synchronization Implications14API design:API specification affects synchronization Implications15program verification: – declare incorrect when synchronization is missing – simplify verification under weak memory models

What expensive synchronization? 16order: read-after-write17 . write X read Y .read Ywrite Xmodern architectures/languagesRead-after write reordering . write X fence read YFence: enforce order Example: Read-after-WriteWhat expensive synchronization? 18atomicity: atomic write-after-read

Atomic Write-after-Read . read X write Y . . read X write X . Examples:compare-and-swapfetch-and-addread-modify-write Which abstract data types ?20AtomicityDeterminismCommutativity Example: Set ADT21 bool add(v) add v bool remove(v) remove v bool contains(v) check if v is in the set

22 Example: Set ADT Example Histories: add(5): true; remove(5): true; ? add(5): true; add(5): false; ? add(5): true; contains(5): true; ?23specification of Set is deterministic Example: Set ADT24 commutativity: a way so that select methods

25 select non-commutative methods26method A is non-commutative if there exists another method B where: A influences B in addition to B influences A27bool add(v) is non-commutative: Example: Set ADT add(v) influences add(v)

28 Example: Set ADT {} add(5): true; add(5): false; (add influences add)29bool remove (v) is non-commutative: Example: Set ADT remove (v) influences remove(v)30 bool contains(v) is commutative: Example: Set ADT contains(v) does not influence add(v), remove(v) or contains(v)

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## Journal Ratings by Circleville Bible College

This Particular Journal got reviewed and rated by 25 select non-commutative methods26method A is non-commutative if there exists another method B where: A influences B in addition to B influences A27bool add(v) is non-commutative: Example: Set ADT add(v) influences add(v) and short form of this particular Institution is US and gave this Journal an Excellent Rating.