CROSS - Centralized Order Book Exchange Service

Author: Matthew Bernardi
Academic Year: 2024/2025
Course: Reti e Laboratorio (LAB2425)

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📌 Project Overview

CROSS (an exChange oRder bOokS Service) is a simplified centralized exchange system for cryptocurrency trading, focusing on BTC/USD pairs. It emulates the core mechanisms behind order matching, execution, and market dynamics—similar to what real-world platforms like Binance or Coinbase use.

The project consists of a multi-threaded server and an interactive client, communicating via TCP and UDP, designed entirely in Java. Orders supported include Market, Limit, and Stop Orders, which are processed following a price/time priority matching algorithm.

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⚙️ Features

✔️ Order Types

• Market Orders: Executed immediately at the best available price. If conditions aren't met, the order is rejected.
• Limit Orders: Executed only if price conditions are satisfied; otherwise queued for future matching.
• Stop Orders: Turn into Market Orders once a defined stop condition is met.

✔️ Core Client Features

• Register/Login/Logout
• Place Market, Limit, and Stop Orders (both Ask and Bid)
• Cancel pending orders
• Request price history (with daily OHLC data)
• Real-time notifications via UDP on order executions

✔️ Server Responsibilities

• Handle multiple clients concurrently using a thread pool
• Maintain persistent storage of users and executed orders (in JSON format)
• Match orders fairly and efficiently
• Send asynchronous UDP notifications on trade executions
• Periodically check and execute pending Stop Orders

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🛠️ Compilation and Execution

You can compile and run the server/client using the provided bash scripts:

./server.sh   # Launch server
./client.sh   # Launch client

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🗃️ Data Structures

• ConcurrentSkipListSet<Order>: for open ask and bid orders, ordered by price and timestamp
• ConcurrentLinkedQueue<User>: stores all registered users
• ConcurrentLinkedQueue<Order>: history of executed orders
• ConcurrentLinkedQueue<Order>: pending stop orders
• LinkedBlockingQueue<Runnable>: server-side task queue

Synchronization is ensured using Java's synchronized blocks when accessing shared structures or writing to files.

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🧵 Thread Architecture

• Client:

  • ClientMain: Main thread, handles CLI interaction and TCP messages
  • ClientUDP: Listens for server-side asynchronous notifications

• Server:

  • ServerMain: Accepts new TCP connections
  • ServerTask: Handles one client per thread
  • ServerUDP: Sends UDP notifications, shared among ServerTasks

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📁 Project Structure

The config/ folder contains the main configuration files and the client.sh and server.sh execution bash scripts, meanwhile the src/ folder contains the source code files.