Barrier is a synchronization construct where a set of processes synchronizes…

Barrier is a synchronization construct where a set of processes synchronizes globally, i.e., each process in the set arrives at the barrier and waits for all others to arrive, and then all processes leave the barrier. Let the number of processes in the set be three, and let S be a binary semaphore with the usual P and V functions. Consider the following C implementation of a barrier with line numbers shown on the left.

void barrier (void) {
1: P(S);
2: process_arrived++;
3: V(S);
4: while (process_arrived != 3);
5: P(S);
6: process_left++;
7: if (process_left == 3) {
8:     process_arrived = 0;
9:     process_left = 0;
10: }
11: V(S);
}

The variables process_arrived and process_left are shared among all processes and are initialized to zero. In a concurrent program, all three processes call the barrier function when they need to synchronize globally.

The above implementation of the barrier is incorrect. Which one of the following is true?