🚂 Multithreaded Train Schedule Server

📖 Overview

Multithreaded Train Server is a high-performance, concurrent Client-Server application designed to simulate a real-time railway management system. Developed in C on Linux, it serves as a central hub (Single Source of Truth) for managing train schedules, tracking real-time delays, and handling ticket bookings for multiple connected clients simultaneously.

The system is built upon a Thread Pool architecture (Pre-threading model), ensuring efficient resource utilization and low latency even under heavy network load.

🚀 Key Features

• Concurrency & Scalability: Utilizes a fixed Thread Pool of 50 worker threads to handle concurrent client connections, eliminating the overhead of dynamic thread creation.
• Data Integrity: Implements robust synchronization using Mutex locks (pthread_mutex) to protect shared resources (RAM data structures and file I/O) against race conditions.
• Real-Time Updates: Allows administrators to report train delays or early arrivals, which are instantly propagated to the system and visible to all clients.
• Data Persistence: Integrates Libxml2 to parse and persist schedule data and ticket availability to an XML database (database.xml).
• Role-Based Access Control: Features a secure login system with distinct roles for Admins (can modify schedules) and Regular Users (can view/book).
• Custom Protocol: Operates over a text-based TCP request-response protocol designed for reliability and ease of debugging.

🛠️ Tech Stack

• Language: C (C11 Standard)
• OS: Linux (POSIX Compliant)
• Networking: TCP/IP Sockets (<sys/socket.h>, <netinet/in.h>)
• Concurrency: POSIX Threads (<pthread.h>)
• XML Parsing: Libxml2 (<libxml/parser.h>)
• Build System: GNU Make

🏗️ Architecture

The application follows a Pre-threaded Server model:

1. Initialization: The Main Thread sets up the TCP socket, loads the database.xml into memory, and spawns a pool of Worker Threads.
2. Connection Handling: Worker threads compete to accept() incoming connections from a shared queue, protected by synchronization primitives.
3. Session Management: Once connected, a dedicated thread handles the client's session until disconnection, processing commands like login, buy_ticket, or get_schedule.
4. Shared Memory: Critical data (train delays, seats) resides in RAM for fast access, with periodic or event-driven writes to the XML file for persistence.

⚙️ Installation & Build

Prerequisites

Ensure you have the GCC compiler and Libxml2 development libraries installed.

On Ubuntu/Debian:

sudo apt-get update
sudo apt-get install build-essential libxml2-dev

Compilation

Clone the repository and compile the source code using make:

git clone [https://github.com/cataCatau/Multithreaded-Train-Server.git](https://github.com/cataCatau/Multithreaded-Train-Server.git)
cd Multithreaded-Train-Server
make

This will generate two executables: server and client.

💻 Usage

1. Start the Server

Run the server first. It listens on port 3010 by default.

./server

2. Start the Client

Open a new terminal window to simulate a user:

./client

Note: To connect from a different machine, update the IP address in client.c before compiling.

🔐 Authentication

The system comes with pre-configured users in users.txt:

Role	Username	Password	Permissions
Admin	admin	admin	Report delays, View schedules
User	catau	Alorap9*	Buy tickets, View schedules

📡 Command Reference

Once connected via the client, use the following commands:

General Commands (No Login Required)

help - Display the list of available commands.

login [username] [password] - Authenticate into the system.

register [username] [password] - Create a new user account.

exit - Disconnect from the server.

Information Commands

get_schedule - Display the complete train schedule.

get_schedule [station] - List trains departing from a specific station.

get_schedule [station] [station] - List trains departing from a specific station and heading to a specific station.

get_train_info [ID] - Show detailed route and status for a train ID.

get_departures [station] - List trains leaving a station in the next hour.

get_arrivals [station] - List trains arriving at a station in the next hour.

get_delays - Show all trains currently delayed.

get_earlys - Show all trains running ahead of schedule.

User Actions (Login Required)

logout - Sign out of the current session.

buy_ticket [TrainID] - Purchase a ticket (decrements available seat count).

Admin Actions (Admin Only)

report_delay [TrainID] [minutes] - Report a delay (updates system & XML).

report_early [TrainID] [minutes] - Report an early arrival.

📂 Project Structure

├── server.c         # Entry point: Server initialization & Thread Pool
├── client.c         # Entry point: Client application
├── commands.c       # Business logic: Command processing & User actions
├── xml_handler.c    # Data Layer: XML parsing (Libxml2) & Persistence
├── shared.h         # Header: Shared data structures (struct tren, constants)
├── database.xml     # Database: Train schedules, routes, and seat counts
├── users.txt        # Database: User credentials
└── Makefile         # Build script for automation

👤 Author

Catalin Tarca

University: Alexandru Ioan Cuza University, Faculty of Computer Science

GitHub: cataCatau