• Installation

 
• Running the demo
• Features
• Keys and actions
• Configuration parameters

 
• Structure of the application
• JavaGroups
• RMI concept
• View Change
• Virtual synchrony problem

 
• Javadoc documentation.

[1] Installation

1. Having sun's jdk1.1.7 installed.
2. Having downloaded javagroups.jar 0.6.6. and swing.jar 1.0.3 and placed in the mud/jar folder.

1. Download the tar gziped file mud.tar.gz.
2. gunzip mud.tar.gz ; tar -xvf mud.tar ( winzip should know how to handle this ).
3. Move the javagroups.jar and the swing.jar to the mud/jar folder
4. cd mud/src
5. Add the JavaGroups and the Swing to your classpath and compile. For example ( in Unix ) :

1. setenv CLASSPATH .:/usr/lib/jdk-1.1.7/lib/classes.zip:/home/mud/jar/swing.jar:/home/mud/jar/JavaGroups.jar
2. gmake

6. To run the program : java Mud

[2] Running the demo

[a] Features

• Monsters - represented by a capital M letter with red color.
• Items - represented by their first letter. Currently there are a : Shield , Potion and Gold.
  The gold doesn't actually give anything.
  The potion raises the health of the player.
  The shield can be used to fight a monster. When armed the hit of the monster is less painful. A drawback is that when the user is armed he can not move to a different spot.
• Other users - users can interact by stealing items from one another and by limiting the movement of another use

[b] Keys and actions

• The user can move around and each move reveals only the area which the user has stepped on to all the users. The movement is done by keypad arrows or by pressing the mouse at the desired location. A player can not make more then one action per 1 second.
• Taking items : a user can take an item by clicking on it and the choosing the action 'take' from the pop up menu.
• Handling items : By clicking on the items on the board / on the items panel the user can activate an action on the item. For example to drink the potion.
• Fight a monster : This action is done automatically when the user is close enough to the monster but only after a certain timeout which gives the player some time to try to escape.

[c] Configuration parameters

    public  static final boolean  DEBUG        = false;
    private static final String   d_mazeFile   = "board.txt";
    public  static final String   GROUP_NAME   = "MUD";  
    public  static final int      CHANNEL_PORT = 9000;
    public  static final int      RMI_TIMEOUT  = 3000;
    public  static final String   PROPS        = "UDP:PING:FD:GMS";
    public  static final int      INITIAL_PLAYER_POWER = 12;    
    public  static final int      INITIAL_MONSTER_POWER = 3;    
  

1. DEBUG : when false no debug print outs will be printed to stderr.
2. d_mazeFile: The maze file is represented by a text file with the first line containing how many lines / rows and the rest is 0/1 separated by new line for each row.
3. PROPS : the layer stack for JavaGroups

[3] Structure of the application

[a] JavaGroups

[b] RMI concept

• d_disp = new Dispatcher ( new JChannelFactory() , props );    // props is the java stack
• d_disp.SetMembershipListener( MudUtil.GROUP_NAME , this );    // enables receiving view changes
• d_disp.Join ( MudUtil.GROUP_NAME , this );    // Joins the group
• d_disp.SendGetN ( MudUtil.GROUP_NAME , parameters , 0 /* number of responses to wait for */ , MudUtil.RMI_TIMEOUT );    // Sends a remote method to be invoked on all members of the group

[c] View change

• JavaGroups triggers ViewAccepted
• ViewAccepted calls rmiGetUserStat for all members. Each member send to all others it's viewId , it's age (round) and it's address.
• After rmiGetUserStat is called for each member the leader is chosen in each node. The leader is chosen to be the one which has the bigger age then all others ( ensuring the correct state ) and in case of equality then there is a lexicographic comparison of urls and ports.
• Leader calls processMasterInit on it's node and saves a new state.
• The state is sent it to all other nodes using rmiStateTransfer
• rmiStateTransfer transfers all the board state + players + monsters + items ... and finally calls board initialization.

[d] Virtual synchrony problem