Question

The Sleeping-Barber Problem:

Answer 1

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);

}