Question

Assume a bus has 25 passenger capacity and has two doors. Add semaphores to the following two functions to ensure that (a) the bus will never be overloaded and (b) passengers will not collide with each other when getting on or getting off the bus. (Hints: Use P operation to decrement the semaphore and V operation to increment the semaphore, specifically you will be using only the following operations: P(&bus), P(&door), V(&bus), V(&door))

semaphore bus = ______;

semaphore door = _____;

getting_off()

{

_________________________________________;

walk_out();

_________________________________________;

} //getting off

getting_on()

{

_________________________________________;

walk_in();

_________________________________________; } //getting on

Answer 1

semaphore bus = 25;

semaphore door = 2;

getting_off()

{

V(&bus);
P(&door);

walk_out();

V(&door);

} //getting off

getting_on()

{

P(&door);

walk_in();

V(&door);
P(&bus); } //getting on