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Towards Automating the Redesign of the Synchronization Skeletons of UPC Programs

Towards Automating the Redesign of the Synchronization Skeletons of UPC Programs. Presenter: Amin Alipour Adviser: Ali Ebnenasir. Motivations. Help developers in automated behavioral debugging, and

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Towards Automating the Redesign of the Synchronization Skeletons of UPC Programs

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  1. Towards Automating the Redesign of the Synchronization Skeletons of UPC Programs Presenter: Amin Alipour Adviser: Ali Ebnenasir

  2. Motivations • Help developers in • automated behavioral debugging, and • design of synchronization mechanisms of multithreaded programs, i.e., synchronization skeleton

  3. Example: A UPC Program

  4. Problem • Deadlock • Need deadlock-freedom

  5. Outline • Problem Statement • Proposed Solution • Case Study

  6. Problem Statement • Input: • A UPC program P • A desired mutual exclusion (e.g., lack of data race) or progress property (e.g., deadlock-freedom), denoted L • P does not meet L • Output: • A revised version of P, denoted P_r • Constraints: • P_r meets L • P_r does not violate other properties of P

  7. Proposed Solution UPC Program Revised UPC Program

  8. Synchronization Skeleton of the UPC Program Synch. Skeleton of thread i // Generate an array element index 0/1 TS_i: { upc_lock(lk[i]); upc_lock(lk[s]); } CS_i: { // Swap ... } // Dont forget to unlock upc_unlock(lk[i]); upc_unlock(lk[s]);

  9. Transforming Synchronization Skeleton to Guarded Commands

  10. Guarded Commands • State: snapshot valuation to program variables • Guarded command: • <grd_1>  stmt_1; • [] <grd_2>  stmt_2; • [] … • [] <grd_n>  stmt_n; • Example: • (x > y)  x := x - y; • [] (y > x)  y := y - x; • A set of transitions (s0, s1)‏ • grd is true in s0, and • s1 is reach by atomic execution of stmt

  11. Canonical UPC Programs • For simplicity, we consider a canonical version of the program with • 2 threads • An array with size 2

  12. Case Study-State TSi Trying Section Thread i CSi Critical SectionThread i LKi Lock of Thread i GLKi Lock for Intra-thread Serialization Thread i Si random value selected by Thread i SSi Whether Thread i has selected a random value

  13. Translation of Synchronization Skeleton to Guarded Commands Initial state values: TS_i := true; CS_i := false; sSet_i = false; Ai1: (sSet_i = false) -> s_i := 0|1; sSet_i := true; Ai2: (sSet_i = true) /\ (TS_i = true) /\ (lk[i] = true) /\ (gotLock_i = false) -> lk[i] := false; gotLock_i := true; Ai3: (sSet_i = true) /\ (TS_i = true) /\ (lk[s_i] = true) /\ gotLock_i = true -> lk[s_i] := false; gotLock_i :=false; TS_i := false; CS_i := true; Ai4: (sSet_i = true) /\ (CS_i = true) /\ (lk[i] = false) /\ (lk[s_i] = false) -> lk[i] := true; lk[s_i] := true; CS_i := false;TS_i := true; sSet_i := false;

  14. Generating Reachability Graph for the program

  15. Reachability Graph Generation • Start with initial states • Check applicable commands • Generate new reachable states • run Steps 1 and 2 until no new state is generated

  16. Finite Model

  17. Finite Model

  18. Finite Model

  19. Finite Model

  20. Automatic Revision

  21. Revised Model

  22. Revised Thread 1 Thread 1 { A11: (!SS1  !S2)  (!SS2 || !S1) ->S1=1; SS1 = true; A12: (TS1 !CS1  LK[0] !GLK1 (S1)  SS1)->LK[0] = false;GLK1 = true; A13: (TS1 !CS1 !LK[0]  GLK1 (S1)  SS1)->LK[1] = false; GLK1=false;TS1 = false;CS1 = true; A14: (!TS1  CS1 !LK[0] !GLK1 (S1)  SS1  SS2)->LK[0] = true; LK[1] = true; CS1 = false;TS1 = true;SS1= false; } Avoid s Deadlock Ai1: (sSet_i = false) -> s_i := 0|1; sSet_i := true; Ai2: (sSet_i = true)  (TS_i = true)  (lk[i] = true)  (gotLock_i = false) -> lk[i] := false; gotLock_i := true; Ai3: (sSet_i = true)  (TS_i = true)  (lk[s_i] = true)  gotLock_i = true -> lk[s_i] := false; gotLock_i :=false;TS_i := false;CS_i := true; Ai4: (sSet_i = true)  (CS_i = true)  (lk[i] = false)  (lk[s_i] = false) -> lk[i] := true; lk[s_i] := true; CS_i := false;TS_i := true; sSet_i := false;

  23. Avoids Deadlock Thread 2‏ { A21: !SS2 ->S2=0; SS2 = true; A22: TS2  !CS2  LK[1]  !GLK2  !(S2)  S1  SS2  !SS1 ->LK[1] = false;GLK2 = true; A23: TS2  !CS2  !LK[1]  GLK2  !(S2)  SS2 ->LK[0] = false; GLK2=false;TS2 = false;CS2 = true; A24: !TS2  CS2  !LK[1]  !GLK2  !(S2)  SS2 ->LK[0] = true; LK[1] = true; CS2 = false;TS2 = true;SS2= false; } Imposes sequential execution Ai1: (sSet_i = false) -> s_i := 0|1; sSet_i := true; Ai2: (sSet_i = true)  (TS_i = true)  (lk[i] = true)  (gotLock_i = false) -> lk[i] := false; gotLock_i := true; Ai3: (sSet_i = true)  (TS_i = true)  (lk[s_i] = true)  gotLock_i = true -> lk[s_i] := false; gotLock_i :=false;TS_i := false; CS_i := true; Ai4: (sSet_i = true)  (CS_i = true)  (lk[i] = false)  (lk[s_i] = false) -> lk[i] := true; lk[s_i] := true; CS_i := false;TS_i := true; sSet_i := false;

  24. Questions

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