Consider two processes, P$1$ and P$2,$ that need to access a shared resource. To ensure mutual exclusion, a

binary semaphore $S$ is used with an initial value of $1.$ The processes follow the given code structure:

a$.$ Explain how the semaphore $S$ ensures mutual exclusion in this scenario.

b$.$ What will happen if the wait$($S$)$ operation is called when $S=0?$