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2025W Operating Systems (CS-3520-01)
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Which of the following tasks would have improved performance if the OS prefetches the next page along with the requested page from disk on page selections?
In the example code from class where we created two threads to update a shared counter, a race condition arose. Which of the following best describes the race condition?
Suppose it takes 50ns to access memory and 5000ns to access disk. To guarantee that Average Memory Access Time (AMAT) is at most 100ns, what must be true about the page-hit-rate H (the percent of pages accessed that are present in physical memory)?
Which page will be evicted?
Recall the code below from class where we used a condition variable to make sure the child runs before the parent prints. Why did we include the int variable done if signalling and waiting is done automatically with condition variables?
int done = 0;
pthread_mutex_t m = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t c = PTHREAD_COND_INITIALIZER;
void thr_exit() {
Pthread_mutex_lock(&m);
done = 1;
Pthread_cond_signal(&c);
Pthread_mutex_unlock(&m);
}
void *child(void *arg) {
printf("child");
thr_exit();
return NULL;
}
void thr_join() {
Pthread_mutex_lock(&m);
while (done == 0)
Pthread_cond_wait(&c, &m);
Pthread_mutex_unlock(&m);
}
int main(int argc, char *argv[]) {
printf("parent: begin");
pthread_t p;
Pthread_create(&p, NULL, child, NULL);
thr_join();
printf("parent: end");
return 0;
}