Assignment 3(problem 1)

[Rahul Shah]

Is the whole shift function atomic or only the *A=*B part is atomic?

I think the whole function should be atomic because if not, suppose 2
process come at the same time.
Initially we consider *A=1;


//Considering *B as key for each process and *A as lock
1. P1 executes *B=*A; //key of P1 is set
2. P2 executes *B=*A; //key of P2 is set
3. P1 executes * A=0;// the Lock variable is 0
4. P2 executes *A=0; // the Lock variable is 0
5. Now if P1 check its key , it will enter into the critical section
6. P2 also check its key and find it set and enters into the critical
section //Mutual exclusion is violated

Instead if the whole SHIFT is atomic we wont have this problem

[Partha Dasgupta]

The whole shift function has to be atomic, for this to work -- both assignments are atomic (together).

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Partha Dasgupta,
School of Computing Informatics, Arizona State University
EMail: par...@asu.edu
http://cactus.eas.asu.edu/partha

[Rahul Shah]

ok cool. That clears my doubt.