Replica management and Consistency

This system consists of a server and multiple client processes. Each client process will connect to the server over a socket connection and register a user name at the server.

The server and the client are managed with a simple GUI. The messages exchanged between server and client use HTTP format.

Each client implements a simple four-function calculator to handle below operations:

• Addition
• Subtraction
• Multiplication
• Division
• Negative numbers
• Decimals to four digits, rounding up

The required actions are summarized as follows:

Client

The client will execute the following sequence of steps:

1. Initialize a local copy of the shared value.
2. Connect to the server via a socket.
3. Provide the server with a unique user name.
4. Wait to be polled by server. While waiting:
   • Allow users to input and execute operations on the four-function calculator.
   • Log user-input in persistent storage.
5. When polled by the server, upload all user-input (sequence of operations) logged since previous poll.
6. Overwrite local copy of shared value with server copy.
7. Notify user local copy has been updated.
8. Repeat at step 4 until the process is killed by the user.

Server

The server will execute the following sequence of steps:

1. Initialize server copy of shared value.
2. Startup and listen for incoming connections.
3. Print that a client has connected and fork a thread to handle that client.
4. When instructed by the user, poll clients for user-input sequence.
5. Display received input sequences from clients on GUI.
6. Apply user-input sequence to server copy of shared value.
7. Push updated copy of shared value to clients.
8. Begin at step 4 until server is closed by the user.

Classes

1. ServerGUI extends javafx.application.Application
2. HTTPServer extends java.lang.Thread
3. ServerThread extends java.lang.Thread
4. ClientGUI extends javafx.application.Application
5. Client extends java.lang.Thread

Compilation

• javac HTTPServer.java
• javac ServerGUI.java
• javac ClientGUI.java

Execution

• java ServerGUI
• java ClientGUI

References

1. JavaFX: Working with the JavaFX Scene Graph – https://docs.oracle.com/javase/8/javafx/scene-graph-tutorial/scenegraph.htm
2. Interface ObservableList<E> – https://docs.oracle.com/javase/8/javafx/api/javafx/collections/ObservableList.html
3. Introducing Threads in Socket Programming in Java – https://www.geeksforgeeks.org/introducing-threads-socket-programming-java/

Note

This code was submitted as part of Distributed Systems course assignment at The University of Texas at Arlington to Prof. Chance Eary (https://mentis.uta.edu/explore/profile/chance-eary)