GATE - 2001 | OS | Consider Peterson’s algorithm for mutual exclusion between two

GATE - 2001 | OS | Consider Peterson’s algorithm for mutual exclusion between two
Posted on 25-02-2022

GATE - 2001 [Operating System]

Questions:

Consider Peterson’s algorithm for mutual exclusion between two concurrent processes i and j. The program executed by process is shown below.

   repeat  

      flag [i] = true;

      turn = j;

      while ( P ) do no-op;

      Enter critical section, perform actions, then exit critical

      section

      flag [ i ] = false;

      Perform other non-critical section actions.

   until false;

For the program to guarantee mutual exclusion, the predicate P in the while loop should be.
(A) flag[j] = true and turn = i
(B) flag[j] = true and turn = j
(C) flag[i] = true and turn = j
(D) flag[i] = true and turn = i

Solution:

Option (B) is Correct.

To ensure the mutual exclusion, we have to take care that ‘turn’ value which is ‘j’ so we should not allow that process in CS which is having flag[j] = true.

 

Thank You

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