Assume the binary variable lock is initialized to be 0, which of the following can be an implementation of the entry section to solve the critical-section problem?
A) while (compare and swap(&lock, 0, 1) != 0), do nothing;
B) while (test and set(&lock)), do nothing;
C) both A and B
D) none of the above

Question

Quizplus · Accepted Answer

Both option A and B are implementations of entry section that solve the critical-section problem. They both use atomic operations to ensure mutual exclusion. Option A uses a compare-and-swap operation to atomically set lock to 1 if it is currently 0, and returns the previous value of lock. The while loop will continue as long as the previous value of lock was not 0, indicating that another process has already entered the critical section. Option B uses a test-and-set operation to atomically set lock to 1 and return its previous value. The while loop will continue as long as the previous value of lock was 1, indicating that another process has already entered the critical section. Both options ensure that only one process can enter the critical section at a time.

Assume the Binary Variable Lock Is Initialized to Be 0