MTech Advanced Operating Systems Lab(14SCS16) (1st sem)
Write a multi-class multithreaded program that simulates multiple
sleeping barbers, all in one barbershop that has a finite number of chairs in
the waiting room. Each customer is instantiated from a single customer class;
each barber is instantiated from a single Barber class.
import
java.util.concurrent.*;
public
class SleepingBarber extends Thread
{
public
static Semaphore customers = new Semaphore(0);
public static Semaphore barber = new
Semaphore(0);
public
static Semaphore accessSeats = new Semaphore(1);
/* the number of chairs in this barbershop is 5.
*/
public
static final int CHAIRS = 5;
public
static int numberOfFreeSeats = CHAIRS;
/* THE CUSTOMER THREAD */
class Customer extends Thread
{
int
iD;
boolean notCut = true;
/* Constructor for the Customer */
public Customer(int i)
{
iD = i;
}
public
void run()
{
while (notCut)
{
// as long as the customer is not cut
try
{
accessSeats.acquire();
if
(numberOfFreeSeats > 0)
{
System.out.println("Customer
"+this.iD+" just sat down.");
numberOfFreeSeats--; //sitting
down on a chair
customers.release(); //notify
the barber that there is a customer
accessSeats.release(); //
don't need to lock the chairs anymore
try
{
barber.acquire();
notCut = false;
this.get_haircut(); //cutting...
}
catch
(InterruptedException ex) {}
}
else
{
//
there are no free seats
System.out.println("There are no
free seats. Customer " + this.iD + "
has left the barbershop.");
accessSeats.release(); //release
the lock on the seats
notCut=false;
}
}
catch
(InterruptedException ex) {}
} //while ends
}
// public void run() ends
/* this
method will simulate getting a hair-cut */
public void get_haircut()
{
System.out.println("Customer
" + this.iD + " is getting his hair cut");
try
{
sleep(5050);
}
catch (InterruptedException ex) {}
}
} //customer class ends here
/* THE BARBER THREAD */
class Barber extends Thread
{
public Barber() {}
public void run()
{
while(true)
{ // runs in an infinite loop
try
{
customers.acquire();
//tries to acquire a customer, if none available,
he goes to sleep
accessSeats.release(); // at this time he has been woken up
numberOfFreeSeats++; //
one chair gets free
barber.release(); // the barber is ready to cut
accessSeats.release(); // no need of lock on the chairs anymore
this.cutHair(); //cutting...
}
catch (InterruptedException ex) {}
}
}
/*
this method will simulate cutting hair */
public void cutHair()
{
System.out.println("The
barber is cutting hair");
try
{
sleep(5000);
}
catch (InterruptedException ex){ }
}
} //barber
class ends here
/* main method */
public static void main(String
args[])
{
SleepingBarber
barberShop = new SleepingBarber(); //Creates a new barbershop
barberShop.start();
}
public void run()
{
Barber b = new
Barber();
b.start(); //Ready
for another day of work
/* This
method will create new customers for a while */
for
(int i=1; i<16; i++)
{
Customer aCustomer = new
Customer(i);
aCustomer.start();
try
{
sleep(2000);
}
catch(InterruptedException
ex) {};
}
}
}// program ends here
Output:
ubuntu@ubuntu-VirtualBox:~/lab$
gedit SleepingBarber.java
ubuntu@ubuntu-VirtualBox:~/lab$
javac SleepingBarber.java
ubuntu@ubuntu-VirtualBox:~/lab$ java SleepingBarber
Customer
1 just sat down.
The
barber is cutting hair
Customer
1 is getting his hair cut
Customer
2 just sat down.
Customer
3 just sat down.
Customer
2 is getting his hair cut
The
barber is cutting hair
Customer
4 just sat down.
Customer
5 just sat down.
The
barber is cutting hair
Customer
3 is getting his hair cut
Customer
6 just sat down.
Customer
7 just sat down.
Customer
8 just sat down.
Customer
4 is getting his hair cut
The
barber is cutting hair
Customer
9 just sat down.
There
are no free seats. Customer 10 has left the barbershop.
Customer
5 is getting his hair cut
The
barber is cutting hair
Customer
11 just sat down.
There
are no free seats. Customer 12 has left the barbershop.
There
are no free seats. Customer 13 has left the barbershop.
Customer
6 is getting his hair cut
The
barber is cutting hair
Customer
14 just sat down.
There
are no free seats. Customer 15 has left the barbershop.
Customer
7 is getting his hair cut
The
barber is cutting hair
Customer
8 is getting his hair cut
The
barber is cutting hair
Customer
9 is getting his hair cut
The
barber is cutting hair
Customer
11 is getting his hair cut
The
barber is cutting hair
Customer
14 is getting his hair cut
The
barber is cutting hair
