Consider how an operating system might implement classical semaphores. Semaphores have two methods P and V

void P ( ) {

if (counter == 0) suspend thread;

counter -- ;

}

void V ( ) {

counter++;

activate one suspended thread if there are any;

}

If these are implemented in the operating system, the OS has access to the scheduling queues.

how the operating system can implement semaphores paying particular attention to the concepts of "suspend" and "activate.