The enter_CS() and leave_CS() functions to implement critical section of a process are realized using test-and-set instruction as follows:

void enter_CS(X) { 
   while test-and-set(X) ; 
} 

void leave_CS(X) { 
  X=0; 
}

In the above solution, X is a memory location associated with the CS and is initialized to 0. Now consider the following statements:

I. The above solution to CS problem is deadlock-free
II. The solution is starvation free.
III. The processes enter CS in FIFO order.
IV More than one process can enter CS at the same time.

Which of the above statements is TRUE?

The P and V operations on counting semaphores, where s is a counting semaphore, are defined as follows:

P(s): s = s-1; 
if s < 0 then wait; 
V(s) : s = s-1; 
ifs <= 0 then wakeup a process waiting on s;

Assume that P_b and V_b the wait and signal operations on binary semaphores are provided. Two binary semaphores X_b and Y_b are used to implement the semaphore operations P(s) and V(s) as follows:

  P(s): Pb (Xb);
        S = s - 1;
        if(s < 0){
          Vb(Xb);
          Pb(Yb);
        }
        Else Vb (Xb);
  V(s): Pb (Xb);
        S = s + 1;
        if(s <= 0) Vb(Yb);
        Vb(Xb);

The initial values of X_b and Y_b are respectively

Two processes, P1 and P2, need to access a critical section of code. Consider the following synchronization construct used by the processes: Here wants1 and wants2 are shared variables, which are initialized to false. Which one of the following statements is TRUE about the above construct?

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 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 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 the three processes call the barrier function when they need to synchronize globally.
The above implementation of barrier is incorrect. Which one of the following is true?