Respuesta :
Answer:
Explanation:
Following are the Semaphores:
Customers: Counts waiting customers;
Barbers: Number of idle barbers (0 or 1)
mutex: Used for mutual exclusion.
Cutting: Ensures that the barber won’t cut another customer’s hair before the previous customer leaves
Shared data variable:
count_cust: Counts waiting customers. ------------copy of customers. As value of semaphores can’t access directly.
// shared data
semaphore customers = 0; semaphore barbers = 0; semaphore cutting = 0; semaphore mutex = 1;
int count_cust= 0;
void barber() {
while(true) { //shop is always open
wait(customers); //sleep when there are no waiting customers
wait(mutex); //mutex for accessing customers1
count_cust= count_cust-1; //customer left
signal(barbers);
signal(mutex);
cut_hair();
}
}
void customer() {
wait(mutex); //mutex for accessing count_cust
if (count_cust< n) {
count_cust= count_cust+1; //new customer
signal(customers); signal(mutex);
wait(barbers); //wait for available barbers get_haircut();
}
else { //do nothing (leave) when all chairs are used. signal(mutex);
}
}
cut_hair(){ waiting(cutting);
}
get_haircut(){
get hair cut for some time; signal(cutting);
}
