3. Sleeping Barber - code

Here are the programs for Semaphore, SleepingBarber and SleepingBarberD described before.
SleepingBarberD differs only by the addition of delay to the customers.



Semaphore.java-----------------------------------
// This count implements a classic counting Semaphore
// It has two synchronized operations which it can perform
// up - increments the count of the semaphore and wakes up
// waiting threads
// down - decrements the count of the semaphore or if zero
// suspends the thread


class Semaphore extends Object
{
private int count;

public Semaphore(int startingCount){
count = startingCount;
}

public void down(){
synchronized (this) {
while (count ‹= 0) {
// We must wait
try {
wait();
} catch (InterruptedException ex) {
// I was interupted, continue onwards
}
}

// We can decrement the count
count--;
}

}

public void up(){
synchronized (this) {
count++;
//notify a waiting thread to wakeup
if (count == 1 ) {
notify();
}
}
}
}
End of Semaphore.java





SleepingBarber.java-------------------------
//Figure 2-36

import Semaphore;

public class SleepingBarber extends Thread {

// Shared objects
// Number of customers waiting for service
public static Semaphore customers = new Semaphore(0);

// Number of barbers waiting for customers
public static Semaphore barbers = new Semaphore(0);

// For mutual exclusion
public static Semaphore mutex = new Semaphore(1);

// Customers are waiting (not being cut)
public static int waiting = 0;

// Chairs for waiting customers
public static final int CHAIRS = 5;

class Barber extends Thread {
private int myNumber; // Id for the Barber

public Barber(int i) { // Constructor for the Barber
myNumber = i;
}

public void run(){ // What a barber does
while(true) {
customers.down(); // Go to sleep if no customers
mutex.down(); // Acquire access to waiting
waiting = waiting - 1; // Decrement count of waiting
// customers
barbers.up(); // One barber is now ready to cut
// hair
mutex.up(); // Release waiting
cut_hair(); // Noncritical region
}
}

public void cut_hair(){
System.out.println("Barber " + myNumber + " is cutting hair");
try {
sleep(7500);
} catch (InterruptedException ex){ }
}
} //end of Barber Class

private class Customer extends Thread {
private int myNumber; // Id for the Customer

public Customer(int i) { // Constructor for the Customer
myNumber = i;
}

public void run(){ // What a customer does
mutex.down(); // Acquire access to waiting
if(waiting ‹ CHAIRS){
waiting = waiting + 1; // Increment count of waiting
// customers
customers.up(); // Wake up barber if needed
mutex.up(); // Release waiting
barbers.down(); // Go to sleep if number of free
// barbers is 0
get_haircut(); // Noncritical region
} else {
mutex.up(); // Shop is full do not wait
}
}


public void get_haircut(){
System.out.println("Customer " + myNumber
+ " is getting his hair cut");
try {
sleep(10000);
} catch (InterruptedException ex){ }
}
} //end of Customer Class


public static void main(String args[]) {

SleepingBarber holder = new SleepingBarber();

holder.start();

}

// This thread spins off a number of customers
public void run(){

final int BARBERS = 3;

Barber aBarber;
Customer aCustomer;

for(int i=0; i‹BARBERS; i++) {
// Create the barbers
aBarber = new Barber(i);

// Start the threads running
aBarber.start();
}

int customerNumber = 0;
while(true){
aCustomer = new Customer(customerNumber++);

// Start the customer running
aCustomer.start();

// Wait a bit and make another customer
try {
sleep(1000);
} catch(InterruptedException ex) {};
}
} //end of run method for SleepingBarber

}
End of SleepingBarber.java---------------------------------------






SleepingBarberD.java---------------------------------------------
//Figure 2-36

import Semaphore;

public class SleepingBarberD extends Thread {

// Shared objects
// Number of customers waiting for service
public static Semaphore customers = new Semaphore(0);

// Number of barbers waiting for customers
public static Semaphore barbers = new Semaphore(0);

// For mutual exclusion
public static Semaphore mutex = new Semaphore(1);

// Customers are waiting (not being cut)
public static int waiting = 0;

// Chairs for waiting customers
public static final int CHAIRS = 5;

class Barber extends Thread {
private int myNumber; // Id for the Barber

public Barber(int i) { // Constructor for the Barber
myNumber = i;
}

public void run(){ // What a barber does
while(true) {
customers.down(); // Go to sleep if no customers
mutex.down(); // Acquire access to waiting
waiting = waiting - 1; // Decrement count of waiting
// customers
barbers.up(); // One barber is now ready to cut
// hair
mutex.up(); // Release waiting
cut_hair(); // Noncritical region
}
}

public void cut_hair(){
System.out.println("Barber " + myNumber + " is cutting hair");
try {
sleep(7500);
} catch (InterruptedException ex){ }
}
} //end of Barber Class

private class Customer extends Thread {
private int myNumber; // Id for the Customer

public Customer(int i) { // Constructor for the Customer
myNumber = i;
}

public void run(){
// What a customer does
mutex.down(); // Acquire access to waiting
if(waiting ‹ CHAIRS){
waiting = waiting + 1; // Increment count of waiting
// customers
customers.up(); // Wake up barber if needed
mutex.up(); // Release waiting

//added section RFC Walters 9 December 2005
try { //random sleep
sleep(10000); //
} catch (InterruptedException e) {} //
try { //random sleep
sleep(10000); //
} catch (InterruptedException e) {} //
try { //random sleep
sleep(10000); //
} catch (InterruptedException e) {} //
//end of added section RFC Walters 9 December 2005




barbers.down(); // Go to sleep if number of free
// barbers is 0
get_haircut(); // Noncritical region
} else {
mutex.up(); // Shop is full do not wait
}
}


public void get_haircut(){
System.out.println("Customer " + myNumber
+ " is getting his hair cut");
try {
sleep(10000);
} catch (InterruptedException ex){ }
}
} //end of Customer Class


public static void main(String args[]) {

SleepingBarberD holder = new SleepingBarberD();

holder.start();

}

// This thread spins off a number of customers
public void run(){

final int BARBERS = 3;

Barber aBarber;
Customer aCustomer;

for(int i=0; i // Create the barbers
aBarber = new Barber(i);

// Start the threads running
aBarber.start();
}

int customerNumber = 0;
while(true){
aCustomer = new Customer(customerNumber++);

// Start the customer running
aCustomer.start();

// Wait a bit and make another customer
try {
sleep(1000);
} catch(InterruptedException ex) {};
}
} //end of run method for SleepingBarber

}

End of SleepingBarberD.java