Operating System
Q221.
Given below is a program which when executed spawns two concurrent processes : semaphore X : = 0 ; /* Process now forks into concurrent processes P1 & P2 */ \begin{array}{|l|l|}\hline \text{$P1$} & \text{$P2$} \\\hline \text{repeat forever } & \text{repeat forever} \\ \text{$V (X) ;$ } & \text{$ P(X) ;$} \\ \text{Compute; } & \text{Compute;}\\ \text{$P(X) ;$ } & \text{$V(X) ;$} \\\hline \end{array} Consider the following statements about processes P1 and P2: I.It is possible for process P1 to starve. II.It is possible for process P2 to starve. Which of the following holds?Q222.
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?Q223.
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?Q224.
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.Which one of the following rectifies the problem in the implementation?Q225.
Processes P1 and P2 use critical_flag in the following routine to achieve mutual exclusion. Assume that critical_flag is initialized to FALSE in the main program. get_exclusive_access ( ) { if (critical _flag == FALSE) { critical_flag = TRUE ; critical_region () ; critical_flag = FALSE; } } Consider the following statements. i.It is possible for both P1 and P2 to access critical_region concurrently. ii.This may lead to a deadlock. Which of the following holds?Q226.
Consider the solution to the bounded buffer producer/consumer problem by using general semaphores S, F, and E. The semaphore S is the mutual exclusion semaphore initialized to 1. The semaphore F corresponds to the number of free slots in the buffer and is initialized to N. The semaphore E corresponds to the number of elements in the buffer and is initialized to 0. \begin{array}{|l|l|}\hline \textbf{Producer Process} & \textbf{Consumer Process} \\\hline \text{Produce an item;} & \text{Wait(E);} \\ \text{Wait(F);} & \text{Wait(S);} \\ \text{Wait(S);} & \text{Remove an item from the buffer;} \\\text{Append the item to the buffer;} & \text{Signal(S);} \\ \text{Signal(S);} & \text{Signal(F);} \\ \text{Signal(E);} & \text{Consume the item;} \\\hline \end{array} Which of the following interchange operations may result in a deadlock? I. Interchanging Wait (F) and Wait (S) in the Producer process II. Interchanging Signal (S) and Signal (F) in the Consumer processQ227.
The following C program: { fork(); fork(); printf("yes"); }If we execute this core segment, how many times the string yes will be printed?Q228.
Which one or more of the following options guarantee that a computer system will transition from user mode to kernel mode?Q230.
The following C program is executed on a Unix / Linux system: #include < unistd.h > int main() { int i; for (i = 0; i < 10; i++) if (i % 2 == 0) fork(); return 0; } The total number of child process created is __________ .