How to Solve Client-Server Concurrent Programming Assignments Effectively

Identifying the Core Requirements

Every concurrent client-server programming assignment consists of fundamental building blocks. In this case, the requirements generally include:

• Establishing a Client-Server Architecture – A system where clients interact with a central server.
• Maintaining Shared Data Structures – Typically, a list (numList) to store randomly generated integers and a variable (total) that holds their cumulative sum.
• Implementing Concurrency – Multiple clients operating simultaneously without interference.
• Ensuring Synchronization – Managing access to shared resources to avoid race conditions.
• Defining a Termination Condition – A condition, such as reaching a specific sum (1 million in this case), to stop execution.

Choosing the Right Technology Stack

• Java RMI (Remote Method Invocation) – Allows method calls between distributed Java applications.
• WebSockets – Provides full-duplex communication over a single TCP connection.
• Thread Synchronization Mechanisms – Essential for managing concurrent access to shared data.
• Random Number Generation – Ensures unique values are processed efficiently by clients.

Understanding the Flow of Execution

• Clients connect to the server and register.
• Clients wait until at least five connections are active.
• Clients generate random numbers every 10ms and send them to the server.
• The server aggregates the numbers and updates the total.
• When the total reaches 1 million, the process halts, and the results are displayed.

Implementing the Solution Step by Step

Setting Up the Server

1. Creating the Server Class

The server must:

• Store and manage shared data.
• Accept multiple client connections.
• Ensure thread-safe updates to shared resources.

import java.rmi.RemoteException; import java.rmi.server.UnicastRemoteObject; import java.util.ArrayList; import java.util.List; public class Server extends UnicastRemoteObject implements ServerInterface { private List<Integer> numList = new ArrayList<>(); private int total = 0; private final Object lock = new Object(); public Server() throws RemoteException {} @Override public synchronized void addNumber(int num) throws RemoteException { synchronized (lock) { numList.add(num); total += num; } } @Override public int getTotal() throws RemoteException { return total; } }

2. Registering the Server

A server registry must be created to allow clients to connect remotely.

import java.rmi.Naming; import java.rmi.registry.LocateRegistry; public class ServerMain { public static void main(String[] args) { try { LocateRegistry.createRegistry(1099); Server server = new Server(); Naming.rebind("rmi://localhost/Server", server); System.out.println("Server is running..."); } catch (Exception e) { e.printStackTrace(); } } }

Implementing the Client

1. Creating the Client Class

The client performs the following tasks:

• Connects to the server.
• Generates random numbers.
• Sends the numbers to the server at regular intervals.

import java.rmi.Naming; import java.util.Random; public class Client { public static void main(String[] args) { try { ServerInterface server = (ServerInterface) Naming.lookup("rmi://localhost/Server"); Random rand = new Random(); int count = 0; while (server.getTotal() < 1000000) { int num = rand.nextInt(13); server.addNumber(num); count++; Thread.sleep(10); } System.out.println("Client finished execution."); } catch (Exception e) { e.printStackTrace(); } } }

Managing Concurrency and Synchronization

• Ensuring Thread Safety
• Using Synchronized Blocks – Prevents multiple threads from modifying shared variables simultaneously.
• Atomic Variables – Ensures atomic updates to shared counters.
• Thread Pools – Efficiently manages multiple client connections.
• Handling Client Connections
• Setting Connection Limits – Ensures that operations begin only when five clients are connected.
• Session Management – Keeps track of active client sessions and disconnections.

Alternative Approach: WebSockets Implementation

Setting Up a WebSocket Server

import javax.websocket.*; import javax.websocket.server.ServerEndpoint; import java.util.concurrent.CopyOnWriteArrayList; @ServerEndpoint("/server") public class WebSocketServer { private static List<Session> clients = new CopyOnWriteArrayList<>(); private static int total = 0; @OnOpen public void onOpen(Session session) { clients.add(session); } @OnMessage public void onMessage(String message, Session session) { synchronized (this) { total += Integer.parseInt(message); if (total >= 1000000) { for (Session client : clients) { client.getAsyncRemote().sendText("Process complete. Total: " + total); } } } } }

Testing, Debugging, and Optimization

Common Issues and Solutions

• Client Timeout Issues – Implement proper exception handling to prevent premature disconnections.
• Deadlocks – Use synchronized methods cautiously and avoid nested locks.
• Resource Cleanup – Ensure proper closure of connections to free up resources efficiently.

Performance Optimization Techniques

• Batch Processing – Instead of sending numbers one at a time, clients can send numbers in batches.
• Efficient Data Storage – Using optimized data structures such as concurrent hash maps.
• Load Balancing – Distributing client requests across multiple server instances for scalability.

Conclusion

Concurrent client-server programming assignments require a structured approach, careful synchronization, and efficient error handling. By implementing solutions using Java RMI or WebSockets, developers can manage multiple client connections effectively while ensuring data consistency and system efficiency. Applying the best practices outlined in this guide will help students successfully navigate such assignments and build robust distributed systems.