1
GATE CSE 2007
MCQ (Single Correct Answer)
+2
-0.6
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?
/* P1 */
while(true){
want s1=true;
while(wants2 == true){
/* Critical Section */
wants1 = false;
}
/* Reminder Section */
}
/* P2 */
while(true){
want s2=true;
while(wants1 == true){
/* Critical Section */
Wants2 = false;
}
/* Reminder Section */
}
2
GATE CSE 2006
MCQ (Single Correct Answer)
+2
-0.6
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.
The above implementation of barrier is incorrect. Which one of the following is true?
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?
3
GATE CSE 2006
MCQ (Single Correct Answer)
+2
-0.6
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.
Which one of the following rectifies the problem in the implementation?
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?
4
GATE CSE 2006
MCQ (Single Correct Answer)
+2
-0.6
The atomic fetch-and-set x, y instruction unconditionally sets the memory location x to 1 and fetches the old value of x n y without allowing any intervening access to the memory location x. consider the following implementation of P and V functions on a binary semaphore S.
void P (binary_semaphore *s) {
unsigned y;
unsigned *x = &(s->value);
do {
fetch-and-set x, y;
} while (y);
}
void V (binary_semaphore *s) {
S->value = 0;
}
Which one of the following is true? Questions Asked from Synchronization and Concurrency (Marks 2)
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