Question

a)Given the following solution for the critical section problem for two processes (the code shown is for processes Pi), show why it does not satisfy the mutual exclusion requirement. Here,lock is a shared variable initialized to FALSE. (Hint: Indicate one scenario where the mutual exclusion requirement is violated.)

do {

           lock = FALSE;

          while (lock);

          lock = TRUE

        Critical section

          /Empty section

          

       Remainder section

}

(b)Does this satisfy the progress requirement? Justify your answer

Answer 1

a Ans)

In the code for every process, there is a local variable "lock" which is made as FALSE. so, irrespective of the shared lock value the lock is made FALSE and every process is entering into the critical section.

Example:

Let say P0 has entered into the critical section by making lock as TRUE and it is not yet left the critical section.

Now P1 is initiated and executes it's the first line of code and make lock as FALSE and enters into critical sections.

which results in the violation of the mutual exclusion principle.

b Ans)

No, it doesn't satisfy the progress requirement. when a process entered into the critical section it makes the lock as TRUE and while leaving the critical section it didn't change the lock value and not allowing other processes to enter into the critical section. so it is not satisfying the progress requirement. To satisfy the progress requirement for any critical section problem it changes the value of lock while it leaving the critical section.