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BankTellerSimulation.java
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218 lines (211 loc) · 6.61 KB
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// threads/BankTellerSimulation.java
// (c)2016 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://mindviewinc.com/Books/OnJava/ for more book information.
// Using queues and multithreading
// {java BankTellerSimulation 5}
import java.util.concurrent.*;
import java.util.*;
// Read-only objects don't require synchronization:
class Customer {
private final int serviceTime;
public Customer(int tm) { serviceTime = tm; }
public int getServiceTime() { return serviceTime; }
public String toString() {
return "[" + serviceTime + "]";
}
}
// Teach the customer line to display itself:
class CustomerLine extends ArrayBlockingQueue<Customer> {
public CustomerLine(int maxLineSize) {
super(maxLineSize);
}
@Override
public String toString() {
if(this.size() == 0)
return "[Empty]";
StringBuilder result = new StringBuilder();
for(Customer customer : this)
result.append(customer);
return result.toString();
}
}
// Randomly add customers to a queue:
class CustomerSupplier implements Runnable {
private CustomerLine customers;
private static SplittableRandom rand = new SplittableRandom(47);
public CustomerSupplier(CustomerLine cq) {
customers = cq;
}
@Override
public void run() {
try {
while(!Thread.interrupted()) {
TimeUnit.MILLISECONDS.sleep(rand.nextInt(300));
customers.put(new Customer(rand.nextInt(1000)));
}
} catch(InterruptedException e) {
System.out.println("CustomerSupplier interrupted");
}
System.out.println("CustomerSupplier terminating");
}
}
class Teller implements Runnable, Comparable<Teller> {
private static int counter = 0;
private final int id = counter++;
// Customers served during this shift:
private int customersServed = 0;
private CustomerLine customers;
private boolean servingCustomerLine = true;
public Teller(CustomerLine cq) { customers = cq; }
public void run() {
try {
while(!Thread.interrupted()) {
Customer customer = customers.take();
TimeUnit.MILLISECONDS.sleep(
customer.getServiceTime());
synchronized(this) {
customersServed++;
while(!servingCustomerLine)
wait();
}
}
} catch(InterruptedException e) {
System.out.println(this + "interrupted");
}
System.out.println(this + "terminating");
}
public synchronized void doSomethingElse() {
customersServed = 0;
servingCustomerLine = false;
}
public synchronized void serveCustomerLine() {
assert !servingCustomerLine:
"already serving: " + this;
servingCustomerLine = true;
notifyAll();
}
public String toString() {
return "Teller " + id + " ";
}
public String shortString() { return "T" + id; }
// Used by priority queue:
public synchronized int compareTo(Teller other) {
return customersServed < other.customersServed ? -1 :
(customersServed == other.customersServed ? 0 : 1);
}
}
class TellerManager implements Runnable {
private ExecutorService exec;
private CustomerLine customers;
private PriorityQueue<Teller> workingTellers =
new PriorityQueue<>();
private Queue<Teller> tellersDoingOtherThings =
new LinkedList<>();
private int adjustmentPeriod;
public TellerManager(ExecutorService e,
CustomerLine customers, int adjustmentPeriod) {
exec = e;
this.customers = customers;
this.adjustmentPeriod = adjustmentPeriod;
// Start with a single teller:
Teller teller = new Teller(customers);
exec.execute(teller);
workingTellers.add(teller);
}
public void adjustTellerNumber() {
// This is actually a control system. By adjusting
// the numbers, you can reveal stability issues in
// the control mechanism.
// If line is too long, add another teller:
if(customers.size() / workingTellers.size() > 2) {
// If tellers are on break or doing
// another job, bring one back:
if(tellersDoingOtherThings.size() > 0) {
Teller teller =
tellersDoingOtherThings.remove();
teller.serveCustomerLine();
workingTellers.offer(teller);
return;
}
// Else create (hire) a new teller
Teller teller = new Teller(customers);
exec.execute(teller);
workingTellers.add(teller);
return;
}
// If line is short enough, remove a teller:
if(workingTellers.size() > 1 &&
customers.size() / workingTellers.size() < 2)
reassignOneTeller();
// If there is no line, we only need one teller:
if(customers.size() == 0)
while(workingTellers.size() > 1)
reassignOneTeller();
}
// Give a teller a different job or a break:
private void reassignOneTeller() {
Teller teller = workingTellers.poll();
teller.doSomethingElse();
tellersDoingOtherThings.offer(teller);
}
@Override
public void run() {
try {
while(!Thread.interrupted()) {
TimeUnit.MILLISECONDS.sleep(adjustmentPeriod);
adjustTellerNumber();
System.out.print(customers + " { ");
for(Teller teller : workingTellers)
System.out.print(teller.shortString() + " ");
System.out.println("}");
}
} catch(InterruptedException e) {
System.out.println(this + "interrupted");
}
System.out.println(this + "terminating");
}
@Override
public String toString() { return "TellerManager "; }
}
public class BankTellerSimulation {
static final int MAX_LINE_SIZE = 50;
static final int ADJUSTMENT_PERIOD = 1000;
public static void
main(String[] args) throws Exception {
ExecutorService es = Executors.newCachedThreadPool();
// If line is too long, customers will leave:
CustomerLine customers =
new CustomerLine(MAX_LINE_SIZE);
es.execute(new CustomerSupplier(customers));
// Manager will add and remove tellers as necessary:
es.execute(new TellerManager(
es, customers, ADJUSTMENT_PERIOD));
if(args.length > 0) // Optional argument
TimeUnit.SECONDS.sleep(new Integer(args[0]));
else {
System.out.println("Press 'Enter' to quit");
System.in.read();
}
es.shutdownNow();
}
}
/* Output:
[768][193][807][125] { T1 T0 }
[125][634][682][267][954][506][639][213] { T2 T0 T1 }
[213][592][770][919][552][727][998][902] { T2 T0 T1 }
[552][727][998][902][769][373][313][683][177][526] { T3 T2
T1 T0 }
TellerManager interrupted
Teller 3 interrupted
CustomerSupplier interrupted
Teller 3 terminating
Teller 2 interrupted
Teller 2 terminating
TellerManager terminating
Teller 1 interrupted
Teller 0 interrupted
Teller 0 terminating
Teller 1 terminating
CustomerSupplier terminating
*/