struct semaphore {
enum value(0, 1);
// q contains all Process Control Blocks (PCBs)
// corresponding to processes got blocked
// while performing down operation.
Queue<process> q;
} P(semaphore s)
{
if (s.value == 1) {
s.value = 0;
}
else {
// add the process to the waiting queue
q.push(P) sleep();
}
}
V(Semaphore s)
{
if (s.q is empty) {
s.value = 1;
}
else {
// select a process from waiting queue
Process p = q.front();
// remove the process from wating as it has been
// sent for CS
q.pop();
wakeup(p);
}
}
