FlashEngine

High-Concurrency Flash Sale Processing System

FlashEngine is a lightweight, high-throughput flash sale processing engine built using Core Java. It simulates real-world e-commerce flash sale events where multiple concurrent users compete for limited inventory. The system leverages Java concurrency primitives to ensure thread safety, prevent overselling, eliminate duplicate purchases, and provide real-time analytics through an embedded HTTP server.

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Features

• Lock-free inventory management using AtomicInteger
• Supports concurrent purchase processing
• Duplicate purchase prevention
• Token bucket rate limiting
• Real-time transaction analytics
• Embedded HTTP server with interactive dashboard
• Zero external dependencies

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Demo

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System Architecture

                    Concurrent Client Requests
                              │
                              ▼
                  Token Bucket Rate Limiter
                              │
                              ▼
               Lock-Free Inventory Allocation
             (AtomicInteger Compare-And-Swap)
                              │
                              ▼
               Duplicate Purchase Prevention
                (ConcurrentHashMap Key Set)
                              │
                              ▼
                 Analytics & Metrics Engine
             (Java Streams + System.nanoTime)
                              │
                              ▼
                 Embedded HTTP Server Dashboard

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Technologies Used

Component	Technology
Language	Java 17+
Concurrency	AtomicInteger, ConcurrentHashMap, ExecutorService, CountDownLatch
Analytics	Java Stream API
Networking	com.sun.net.httpserver.HttpServer
Frontend	HTML, CSS, JavaScript
Dependencies	None

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Project Structure

FlashEngine-Java/
│
├── Main.java
├── WebServer.java
├── FlashSaleService.java
├── Product.java
├── PurchaseRecord.java
├── PurchaseResult.java
├── RateLimiter.java
├── SaleAnalytics.java
├── DuplicatePurchaseException.java
├── OutOfStockException.java
├── RateLimitExceededException.java
├── README.md
├── LICENSE
└── assets/
    └── flashengine-demo.gif

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Core Components

Lock-Free Inventory Management

Inventory updates are performed using AtomicInteger and Compare-And-Swap (CAS) operations, ensuring thread-safe stock allocation without explicit locks.

Rate Limiting

A token bucket rate limiter restricts each user to a fixed number of requests per second, protecting the system from excessive traffic.

Duplicate Purchase Prevention

A thread-safe ConcurrentHashMap.newKeySet() is used to ensure that each user can complete only one successful purchase during a flash sale.

Analytics Engine

Execution metrics are collected using System.nanoTime() and aggregated using the Java Stream API to calculate:

• Total successful purchases
• Failed transactions
• Average latency
• Minimum latency
• Maximum latency
• Total revenue

Embedded HTTP Server

The application includes a lightweight web server built using com.sun.net.httpserver.HttpServer that serves an interactive dashboard and REST endpoints.

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Sample Analytics Output

{
  "analytics": {
    "totalAttempts": 100,
    "successfulOrders": 10,
    "outOfStockCount": 85,
    "rateLimitedCount": 5,
    "totalRevenue": 4999.90,
    "avgLatencyMs": 0.412,
    "minLatencyMs": 0.085,
    "maxLatencyMs": 1.840
  }
}

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Performance Configuration

Parameter	Value
Concurrent Threads	100
Initial Stock	10 Items
Product Price	$499.99
Rate Limit	3 Requests/Second/User
Inventory Overselling	Prevented

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How to Run

Prerequisites

• Java 17 or later
• Git

Clone the Repository

git clone https://github.com/Shreeja-88/FlashEngine-Java.git
cd FlashEngine-Java

Compile

javac *.java

Run the Web Server

java WebServer

or run the simulation directly

java Main

Open the Dashboard

http://localhost:8080

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Java Concepts Demonstrated

• Multithreading
• ExecutorService
• Atomic Operations
• Compare-And-Swap (CAS)
• ConcurrentHashMap
• CountDownLatch
• Java Stream API
• Custom Exceptions
• Embedded HTTP Server
• RESTful API Design
• Thread-Safe Programming

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