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Two processes X and Y need to access a critical section. Consider the following synchronization construct used by both the processes
Process X
/* other code for process X */
while (true)
{
varP = true;
while (varQ == true)
{
/* critical section */
varP = false;
}
}
/* other code for process X */
Process Y
/* other code for process Y */ while (true)
{
varQ = true;
while (varP == true)
{
/* critical section */
varQ = false;
}
}
/* other code for process Y */
Here, varP and varQ are shared variables and both are initialized to false. Which one of the following statements is true?
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- The proposed solution prevents deadlock but fails to guarantee mutual exclusion
- The proposed solution guarantees mutual exclusion but fails to prevent deadlock
- The proposed solution guarantees mutual exclusion and prevents deadlock
- The proposed solution fails to prevent deadlock and fails to guarantee mutual exclusion
- The proposed solution prevents deadlock but fails to guarantee mutual exclusion
Correct Option: A
varP = varQ = FALSE Initially.
Assume that, process X is willing to enter into critical section. So it makes varP = True, then if processor switches to process Y, then process Y can enter into critical section.
After entering into the critical section, then if processor switches to process X, then process X also can enter into the critical section. It is clearly showing that both are in critical section at a time which leads to “failing to guarantee material exclusion”
To enter into the critical section process X is not waiting for process Y and vice versa. So we can “Prevent Deadlock” so, overall, option (a) is correct.
