li tak sing comps311f. case study: consumers and producers a fixed size buffer which can hold at...

Li Tak Sing

COMPS311F

Case study: consumers and producersA fixed size buffer which can hold at most

certain integers.A number of producers which generate

integers randomly at random intervals. The integers will then be put into the buffer.

A number of consumers which get integers from the buffer at random intervals.

File locationThe application can be accessed at:

http://plbpc001.ouhk.edu.hk/~mt311f/examples/mt3112010/build/classes/CP.html

The source file can be obtained at:http://plbpc001.ouhk.edu.hk/~mt311f/

examples/mt3112010/src/CP.java

Colour codingblack: The thread is trying to lock the bufferblue: The thread has release the lock

because it cannot process.green: The thread is sleeping.red: The thread has finished the current

task.orange: The thread has acquired the lock of

the buffer.

Attributesprivate int size = 3;private Producer[] p;private Consumer[] c;private javax.swing.JButton stack[] = new

javax.swing.JButton[size];private int no = 0;

The put method private synchronized void put(int i, Producer p) {

p.setStatus("locking " + i);

try {Thread.sleep(1000);} catch (Exception e) {};

while (no == size) {

try {

p.setStatus("waiting to put " + i);

wait();

} catch (Exception e) {

}

}

notifyAll();

stack[size-(++no)].setText(Integer.toString(i));

p.setStatus("put "+i);

try {Thread.sleep(1000);} catch (Exception e) {};

}

The get method private synchronized int get(Consumer p) {

p.setStatus("locking");

try {Thread.sleep(1000);} catch (Exception e) {};

while (no == 0) {

try {

p.setStatus("waiting to get ");

wait();

} catch (Exception e) {

}

}

notifyAll();

The get method int i = 0;

try {

i = Integer.parseInt(stack[size-(no)].getText());

stack[size-no].setText("");

no--;

} catch (Exception e) {

}

notifyAll();

p.setStatus("got "+i);

try {Thread.sleep(1000);} catch (Exception e) {};

return i;

}

CPButtonThis is the class of both Producer and

Consumer. It is a JButton and has implemented the

Runnable interface.

Producer public void run() {

while (true) {

try {

int number = (int) (Math.random() * 10);

setStatus("putting "+number);

put(number,this);

int interval = ((int) (Math.random() * 10000));

this.setStatus("sleeping "+(interval/1000)+"secs");

Thread.sleep(interval);

} catch (Exception e) {

}

}

}

Consumer public void run() {

while (true) {

try {

setStatus("getting");

int number=get(this);

int interval = ((int) (Math.random() * 10000));

this.setStatus("sleeping "+(interval/1000)+"secs");

Thread.sleep(interval);

} catch (Exception e) {

}

}

}

NetworkingThere are two modes: connection oriented

and connectionless.The connection oriented mode works like

telephone lines. Before you can talk to another person over the phone, you need to establish a circuit connecting you and the other person. Then, you can use this circuit to transmit voice signal. The signal will always arrive in the same order as they are sent.

Connectionless modeThe connectionless mode works like the

post office. When you send a letter to another person, the post office will deliver the letter to that person. However, if you send many letters to the same person, there is no guarantee that the letter will arrive at the same order as they are sent.

IP address and PortBefore we can communicate with a

computer, we need to know how to locate that computer first.

Computers are identified by its IP address in the internet.

An IP address consists of four bytes and are usually expressed in the form of: xxx.xxx.xxx.xxx

Since IP address is difficult to remember, we usually use host name instead.

Host name and domain name serverNote that IP addresses and host names do

not form a one to one relation. An IP address can map to zero, one or even

more host names.Similarly, a host name can also map to

zero, one or even more IP addresses.

port A computer can have many services. For

example, a server would usually provide services like http, ftp, telnet etc. So when you want to talk to a computer, you need to specify which service you want to use.

This is done by specifying the port number corresponding to the service.

portA port number is a 2 bytes integers starting

from 1. Some common services use pre-defined

port: ftp: 21, telnet: 23, http: 80 etc.So when two computers are connected

using the connection oriented mode, the connection is identified uniquely by the ip addresses and the ports used by the two computer.

IP: 123.3.24.22 IP: 202.40.219.235

port 3334 port 234

A connection is uniquely identified by the IP addresses and port numbers at the two ends.

ServerThe ip address and port number work like a

telephone with some extension. So you want to be a server, it is similar to one who is wait for others to call. So the first thing he/she needs to do is to let others to know the telephone number and the extension number.

ServerHowever, when other people want to talk to

the server, there is no need to use a particular telephone and extension. You can use any one that is available.

ServerIf the server is a multithreaded server, then

the server can be talking to a number of clients at a time.

IP: 123.3.24.22 IP: 202.40.219.235

port 3334 port 234

A connection is uniquely identified by the IP addresses and port numbers at the two ends.

IP: 223.33.44.103

port 8242

ServerSo, even though a server is waiting for

requests at one port only, it is possible for it to entertain many requests at the same time.

SocketSocket is the term used to describe one

end of a connection. So to create a connection between two

computers, you first need to have two sockets at the two ends.

SocketsThere are two kinds of sockets, one on the

server and one on the client.As mentioned earlier, when you need to

specify the port to be used on the server side.

In Java, ServerSocket is used to model sockets on the server side.

ServerSocketthe constructor

public ServerSocket(int port)throws IOException

can be used to create a socket on the server side with the given port. The constructor will throw IOException if there is a problem in creating the server socket.

SocketAfter the ServerSocket is created, then we

can make the server listen to the port by invoking the accept method of ServerSocket:

ServerSocket sSocket=new ServerSocket(4444);Socket socket=sSocket.accept();

When the accept method is invoked, the thread is blocked until there is a request from a client for this service.

SocketThen, a Socket will be returned.As said earlier, a socket is one end of a

network connection. To start the communication, you need to get an input stream and an output stream by using the method:

InputStream getInputStream() throws IOExceptionOutputStream getOutputStream() throws IOException

A single threaded serverSo a single threaded server would do

something like this:

ServerSocket sSocket=new ServerSocket(11111);

while (true) {

Socket socket=sSocket.accept();

OutputStream outputStream=socket.getOutputStream();

InputStream inputStream=socket.getInputStream();

.... // we can do something about the input and output.

}

The clientOn the client side, there is no need to

create a ServerSocket. Instead, we would use a constructor of Socket:

public Socket(String host, int port) throws UnknownHostException, IOException

Note that we need to specify the host and the port number here. To specify the host, you can either use the IP address or the host name.

localhostIf you have two computers, you can use

one computer as the server and the other as the client to test your network program.

However, if you only has one computer, how can you test a network program?

You can do that by using the loopback address: 127.0.0.1 which refers to your computer.

A simple serverLet's write a simple single threaded server

which accepts two integers from a client and then returns the sum of the two integers to the client.

public class MyServer {

static public void main(String st[]) {

try {

java.net.ServerSocket sSocket=new java.net.ServerSocket(11111);

while (true) {

java.net.Socket socket=sSocket.accept();

java.io.OutputStream output=socket.getOutputStream();

java.io.InputStream input=socket.getInputStream();

java.io.DataOutputStream dout=new java.io.DataOutputStream(output);

java.io.DataInputStream din=new java.io.DataInputStream(input);

int a1=din.readInt();

int a2=din.readInt();

dout.writeInt(a1+a2);

dout.close();

din.close();

socket.close();

}

}

catch (Exception e) {

}

}

}

public class MyClient {

public static void main(String st[]) {

try {

java.net.Socket socket=new java.net.Socket("127.0.0.1",11111);

java.io.OutputStream output=socket.getOutputStream();

java.io.InputStream input=socket.getInputStream();

java.io.DataOutputStream dout=new java.io.DataOutputStream(output);

java.io.DataInputStream din=new java.io.DataInputStream(input);

dout.writeInt(3);

dout.writeInt(4);

int result=din.readInt();

System.out.println("the result is "+result);

} catch (Exception e) {

}

}

}

A multithreaded serverThe previous server can only handle one

request at a time. This does not seem to be a problem as each request does not last for too long.

However, if a server needs to provide some computationally intensive service, there is a need to have a multithreaded server or else a client may have to wait for a long time before it is served.

Multithreaded serverIn a multithreaded server, when there is an

incoming request, we would create a thread to handle the request.

Now, lets rewrite the last simple server to be a multithreaded server.

Multithreaded serverFirst we create a class MyThread which is

used to handle a request. In our design, the constructor of MyThread has a parameter of type Socket which is the socket returned from the accept method of ServerSocket.

Then the run method of MyThread would perform the necessary operations.

public class MyThread extends Thread {

private java.net.Socket socket;

/** Creates a new instance of MyThread */

public MyThread(java.net.Socket socket) {

this.socket=socket;

}

public void run() {

try {

java.io.OutputStream output=socket.getOutputStream();

java.io.InputStream input=socket.getInputStream();

java.io.DataOutputStream dout=new java.io.DataOutputStream(output);

java.io.DataInputStream din=new java.io.DataInputStream(input);

int a1=din.readInt();

int a2=din.readInt();

dout.writeInt(a1+a2);

dout.close();

din.close();

socket.close();

} catch (Exception e) {}

}

}

public class MultiThreadedServer {

static public void main(String st[]) {

try {

java.net.ServerSocket sSocket=new java.net.ServerSocket(11111);

while (true) {

java.net.Socket socket=sSocket.accept();

MyThread thread=new MyThread(socket);

thread.start();

}

}

catch (Exception e) {

}

}

}