Auction System Simulation

Overview

This repository contains a Java-based simulation of an auction system, designed to mimic real-world auction dynamics. It offers a robust platform for listing items for auction and placing bids, with a focus on handling complex scenarios including concurrent bidding.

Purpose of the Simulation

The primary aim is to demonstrate effective handling of various auction scenarios, particularly focusing on concurrency and compliance with common auction rules.

Auction Rules

The application adheres to these rules:

• Auction Time Frame: Bids are valid if placed after the auction start time and before or on the closing time.
• Bid Validity: A bid is valid if it is higher than previous bids made by the same user.
• Winning Criteria:
  • If only one valid bid is received, the item is sold at the reserve price.
  • If multiple bids are received, the highest bidder wins but pays the price of the second-highest bid.
  • In the event of equal bids, the earliest bid prevails.
• No Bids: Without valid bids, the item remains unsold.

Implementation Details

Data Structures and Algorithms

• ConcurrentHashMap: Utilized for storing active auctions (auctions) and auction results (auctionResults) in the AuctionManager class, ensuring thread-safe operations.
• TreeMap: Employed within each Auction instance to store bids in a reverse-sorted order for efficient highest and second-highest bid retrieval.

Synchronization and Thread Safety

• ReentrantLock: Used within the Auction class to ensure thread safety for operations like bid placement and auction finalization.
• Shared Variables: Critical for maintaining the state of auctions and handling concurrent access.

Techniques

• Concurrency Handling: Demonstrates handling of concurrent bid submissions using ExecutorService in unit tests to simulate real-world auction scenarios.
• Thread Safety: Ensures consistent and accurate auction processing in a multi-threaded environment.

Input and Output Formats

Input

Actions are represented as pipe-delimited strings:

• SELL: timestamp|user_id|SELL|item|reserve_price|close_time
• BID: timestamp|user_id|BID|item|bid_amount
• Heartbeat: timestamp

Output

Each completed auction outputs:

• close_time|item|user_id|status|price_paid|total_bid_count|highest_bid|lowest_bid

Unit Test Cases

The repository includes comprehensive tests for scenarios like:

• Single Bid Wins and Pays Reserve Price
• Highest Bidder Pays Second Highest Price
• Auction with No Bids
• Concurrent Bidding
• Bid at Closing Time These tests, located in src/test/java/..., validate the functionality of the auction system.

Project Demonstration

This project demonstrates:

• Effective concurrent operations handling in software applications.
• Application of data structures (ConcurrentHashMap, TreeMap) for real-world problem-solving.
• Implementation of synchronization (ReentrantLock) for thread safety in multi-threaded environments.
• Adherence to complex auction rules and handling of various auction outcomes.