Multiplayer Game Programming 2/26

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Martha Parker
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1 Multiplayer Game Programming 2/26 1. Turn off Windows Firewall 2. Download and install Python and Notepad++ a. Python.org downloads/python/install b. Notepad-plus-plus.org download/install 3. Download and run TCPView. a. Go to the web page b. Click Downloads, click Networking Utilities, and click TCPView. c. Download the zip file and unzip. d. Create a new folder named sysinternals. e. Unzip the TCPView program and copy it into the sysinternals folder. f. Run TCPView. 4. TCP and UDP Connections TCP slower but guarantees delivery UDP faster but no guarantee of delivery 5. Clients and Servers find each other by IP addresses 6. Applications work on Port numbers Connect to Address using Port Web uses port Well known ports Registered Ports Basic Client and Server program logic: a. Server i. Start and listen on port for incoming connection - loop ii. Client sends request to talk to server iii. Server opens connection and starts sending/receiving to client based on protocol b. Client i. Send request packet to Server on specified port ii. Waits for server to respond with port connection (packet level) iii. Starts talking to server based on protocol

2 8. Problems with basic program logic a. Maintaining multiple client connections to Server b. Blocking Port Server opens and then blocks the port from other connections while it waits for the client to send/receive data. 9. One way to solve the blocking operation is to use Threads. Each connection is started on its own thread and the server operations handle a multi-threaded conversation. (Threads are lightweight Processes) Threads share memory/storage while Processes are operating system based and do not (by default) share memory and interrupt space. (Pipelines can be created between processes). There are several problems with multithreading in large games. Creating and maintaining threads is expensive in terms of resources and parallel threads must be kept in sync. 10. Another way is using the socket non-blocking mode. When a socket is set to non-blocking mode the socket returns an error code if there is nothing to be done and returns the data when there is something there. In this way the server program and store the connections to a data structure (array) and then inside each game loop look at the socket and see if there is incoming data.

11. Using Eclipse a. Eclipse is a project oriented development environment. b. Click File/New/Project c. Choose Java/Java Project d. Click next. e. In the Project 12. Adding Python to Eclipse a.

3 11. Using Eclipse a. Eclipse is a project oriented development environment. b. Click File/New/Project c. Choose Java/Java Project d. Click next. e. In the Project 12. Adding Python to Eclipse a. Click Help and choose Install New Software b. In Works with type c. Click PyDev check box and install. You may be asked for accept various options. d. Click Window/ Preferences. e. Set the following settings

4 You need to make sure that the Python Interpreter points to python.

5 13. Basic Java Project a. Start Eclipse and close Welcome Window b. Click File/New/Project. You see the project window. c. Click Next. You see the Project setting dialog box d. For the Project Name type JavaTestOne and click the Finish button. This creates a folder in the Eclipse workspace area with this project name. e. Don t create a Java Module. f. If asked, switch to the Java Perspective g. In the left window you see the Package Explorer and the project just created.

6 h. Right click the Project icon, select New, and select Class

i. In the Window dialog enter the class name JavaTestClass and click the main check box j. Click Finish to create the class. You now have a basic main class in your project. 14. Importing Libraries a.

7 i. In the Window dialog enter the class name JavaTestClass and click the main check box j. Click Finish to create the class. You now have a basic main class in your project. 14. Importing Libraries a. Java has a set of Java Libraries that provide basic functionality. When writing code you want to import and use these libraries. This can be done automatically in Eclipse. b. Create a new Java Project and add a basic Java Class with a main(). c. Above the line with public static void main and below the line with public class type: Scanner kbd; d. You see the word Scanner underlined in red. This means that this library has not been imported.

Java Exceptions (https://docs.oracle.com/javase/tutorial/essential/exceptions/index.html) a. Java uses and Exception handling architecture to manage errors in code.

8 e. Move the mouse over the word Scanner. You see a popup f. Click the Import Scanner (java.util) link to automatically import this library. g. Below the line with public static void main type: kbd = new Scanner(System.in) notice that kbd is underlined. h. Move the mouse over the underlined kbd and click change kbd to static. 15. Java Exceptions ( a. Java uses and Exception handling architecture to manage errors in code. The purpose of Exceptions is to jump out of loops when an error happens and not to try and cascade errors down through a block of code. Exceptions will jump to the catch part of the exception or (if not caught) jump to the operating system and have it handle the exception. b. Edit your new Java project so it looks like: c. Move the mouse over the File and FileReader words and add the library files. You now have the new FileReader(file) text underlined.

Try/Catch block: f. A try/catch block is now enclosing you code.

9 d. Using the mouse select the two lines of text you just typed: e. Right click the selected text and choose Surround With and then choose Try/Catch block: f. A try/catch block is now enclosing you code. To check what kind of exception the statement will generate you can move the mouse over the command.

10 The Surround With command looks at the methods being used and automatically figures out what Exception will be thrown. g. Move the mouse over the second FileReader() function. You see the Java documentation for this command: h. Notice that the Throws: option tells you what exception will be thrown.

i. Select the try/catch block and remove the File and FileReader lines of code so all you have is: 16. Java Threading a. One way to handle client connections is with a Java Threading server.

11 i. Select the try/catch block and remove the File and FileReader lines of code so all you have is: 16. Java Threading a. One way to handle client connections is with a Java Threading server. This will create a new thread for each client connection. The thread will handle input and output with the client. 17. Java Threading Example: a. Edit your project code so it looks like: import java.util.scanner; public class JavaTestClass { static Scanner kbd; public static void main(string[] args) { // TODO Auto-generated method stub kbd = new Scanner(System.in); MyThreadClass c1 = new MyThreadClass("Frank", 5000); MyThreadClass c2 = new MyThreadClass("Donna", 8000); c1.start(); c2.start(); while (true) { if( c1.getnumlives() == 0 && c2.getnumlives()==0) break;

12 System.out.println("What is your name?"); String n = kbd.next(); System.out.println("Hello "+n); System.out.println("All done"); class MyThreadClass extends Thread { private String name; private int pausenum; private int numlives; public MyThreadClass(String n, int p) { name = n; pausenum = p; numlives = 10; public int getnumlives() { return numlives; public void run() { while (numlives > 0) { System.out.println("Hello: I am " + name); numlives--; try { Thread.sleep(pausenum); catch (InterruptedException e) { e.printstacktrace();

13 b. Run the program. 18. Java Networking Client a. Create a new Java Project named JNetProject. b. Create a new class named myjavaclient. c. Enter the following code: import java.io.*; import java.net.*; import java.util.scanner; public class myjavaclient { private static Scanner kbd; public static void main(string[] args) { // TODO Auto-generated method stub kbd = new Scanner(System.in); if(args.length!=2) { System.out.println("Error: must supply host ip and port"); System.out.println("Example:java -jar myjavaclient<host><port>"); System.exit(0); String hostname = args[0]; String portstr = args[1]; int port = Integer.parseInt(portstr); Socket clientsock=null; try { InetAddress addr = InetAddress.getByName(hostname); System.out.println("Connecting..."); clientsock = new Socket(addr,port); // wait for connection System.out.println("Connected"); // get buffers PrintWriter out = new PrintWriter(clientsock.getOutputStream(),true); BufferedReader in = new BufferedReader(new InputStreamReader(clientsock.getInputStream())); // go into write loop boolean stoptalking = false; while(stoptalking==false) { String msgin; String msout; System.out.print("==> "); msgin = kbd.next(); if( msgin.equalsignorecase("stop")) { stoptalking=true; out.println("bye");

14 else { clientsock.close(); continue; out.println(msgin); catch (UnknownHostException e) { // TODO Auto-generated catch block e.printstacktrace(); catch (IOException e) { // TODO Auto-generated catch block e.printstacktrace(); 19. Viewing Socket Connections netstat -an Python Server a. In Eclipse, choose File, choose New, and choose Other.

15 b. In the project window choose PyDev and choose PyDev Project c. Click Next.

16 d. In the PyDev project window set the project name and the interpreter (you must have preciously set the location of the python.exe file). e. Click Finish and change to the python development perspective. f. Right click the pydevserver project, choose New and choose File. g. In the project window make sure you have selected the parent folder (pydevserver). h. For the file name type pydevsrv.py and click Finish. In the Python editor window enter the following code: import socket import sys

17 # check arguments if len(sys.argv)<2: print("must give me IP address and port") host = input("enter your IP address ") port = input("enter your port number ") else: host = sys.argv[1] port = sys.argv[2] try: socket.inet_aton(host) print("ip address looks ok") except socket.error: print("strange IP address "+host+"??? ") sys.exit() try: int(port) print("port looks good") except: print("strange port") sys.exit() # Create a TCP/IP socket sock = socket.socket(socket.af_inet, socket.sock_stream) p = int(port) # Bind the socket to the port sock.bind((host, p)) # Listen for incoming connections sock.listen(1) # Wait for a connection print( "waiting for a connection") connection, client = sock.accept() print (client, "connected") # Receive the data in small chunks and retransmit it

18 cflag=true while(cflag==true): print(cflag) data=connection.recv(1024) d = data.decode('utf-8').strip() if(data): print(d) if(d == "bye"): cflag=false connection.close() sys.exit(1) # Close the connection connection.close() i. Run your program (click the green Run button) j. Enter your computer s IP address and the port number k. Change over to your Java client program and run it. l. Enter the same IP address and the same port number.

Concurrency and Java Programming

Concurrency and Java Programming What is Concurrent Programming? Concurrent programming involves using features of the Java VM that allow parts of your program to run in parallel with each other. This