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CW Concurrent Write

P=1 1 j M. P=N 1  i  N 1  j  M. ER Exclusive Read. EW Exclusive Write. CR Concurrent Read. CW Concurrent Write. P=1 1 j M. P=N 1  i  N 1  j  M. ER. P 1  m j. P i  m j. EW. P 1  m j. P i  m j. CR.  i , P i  m j. CW.  i , P i  m j. BSR-.

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CW Concurrent Write

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  1. P=1 1j M P=N 1  i  N 1  j  M ER Exclusive Read EW Exclusive Write CR Concurrent Read CW Concurrent Write

  2. P=1 1j M P=N 1  i  N 1  j  M ER P1 mj Pi mj EW P1 mj Pi mj CR i, Pi mj CW i, Pi mj

  3. BSR- • Broadcast. Each Pi broadcasts a datum & tag, di & gi, respectively, to all M memory locations. So, i j, Pi sends < di , gi > to Uj, 1  i  N , 1  j  M

  4. BSR- • Selection. Each Uj uses a “limit”, lj , with a selection rule,  , to test gi. • So, evaluate gi lj where  :  ,  ,  ,  ,  ,  • If gi lj is TRUE, then di is selected (accepted) for the reduction phase, else it is rejected by Uj.

  5. BSR- • Reduction. All di’s selected by Uj are combined (or reduced) into one datum using a binary associative reduction operator, R , with R being SUM, PRODUCT, AND, OR, XOR, MAX, MIN    V    • Result is stored in Uj.

  6. Always question, never blindly accept (things are not always what they seem!). Further, there are always implications... • If all memory accesses take log(M) time, is there any such thing as a constant time operation/algorithm? • Does this somehow imply that it is possible to break O(1)?

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