Java Concurrency Trading System

A comprehensive demonstration of Java concurrency concepts through realistic trading system scenarios. This project covers all major concurrency topics essential for senior-level interviews and building high-performance financial systems.

🎯 Project Overview

This project implements a complete trading system using Java 21, demonstrating every aspect of Java concurrency through practical, real-world scenarios. Each concept is illustrated with working code that you might encounter in actual trading, banking, or financial technology systems.

🚀 Features

Core Concurrency Concepts Covered

1. Java Memory Model (JMM) - Market data visibility and happens-before relationships
2. Thread Basics - Order processing lifecycle and thread management
3. Synchronization Primitives - Portfolio management with synchronized, volatile, and locks
4. Thread Coordination - Trade settlement with CountDownLatch, CyclicBarrier, Semaphore, Phaser
5. Executors & Thread Pools - Order execution engines with different pool types
6. Concurrent Collections - Order books and trade history with thread-safe collections
7. Futures & Async Programming - Non-blocking trading operations with CompletableFuture
8. Concurrency Patterns - Producer-Consumer, Work Stealing, Actor Model, Immutable Objects
9. Project Loom Virtual Threads - High-frequency trading scalability with Java 21

Trading System Components

• Market Data Feed - Real-time price updates with concurrent access
• Order Management - Thread-safe order processing and validation
• Portfolio Management - Concurrent position tracking and risk management
• Trade Settlement - Multi-phase settlement coordination
• Risk Management - Concurrent risk checks and limits
• Order Book - Thread-safe order matching and execution
• High-Frequency Trading - Massive scalability with virtual threads

🛠️ Requirements

• Java 21 (with Project Loom support)
• Gradle 8.5+
• 8GB+ RAM (recommended for virtual thread demonstrations)

🚀 Quick Start

Option 1: Simple Demo (No external dependencies)

The simple demo runs with just the JDK and demonstrates core concepts:

# Linux/Mac - Use shell script
./simple-compile.sh
java -cp build/classes me.valizadeh.practices.SimpleDemo

# Windows - Use batch file
simple-compile.bat
java -cp build/classes me.valizadeh.practices.SimpleDemo

# Manual compilation (all platforms)
javac -d build/classes -cp "src/main/java" src/main/java/me/valizadeh/practices/model/*.java src/main/java/me/valizadeh/practices/SimpleDemo.java
java -cp build/classes me.valizadeh.practices.SimpleDemo

Option 2: Full System (With Gradle)

The complete system with all features requires Gradle and dependencies:

# With Gradle installed
./gradlew run

# Interactive mode
./gradlew run --args="interactive"

# Build only
./gradlew build

Option 3: Manual Compilation Test

# Linux/Mac
./test-compile.sh

# Windows
.\test-compile.bat

# This will show compilation status (note: logging dependencies required for full system)

📁 Project Structure

src/main/java/me/valizadeh/practices/
├── TradingSystemDemo.java              # Main application (full system)
├── SimpleDemo.java                     # Simple demo (no dependencies)
├── model/                              # Trading domain models
│   ├── Trade.java                      # Immutable trade record
│   ├── MarketData.java                 # Market data record
│   ├── Portfolio.java                  # Portfolio state
│   └── OrderBookEntry.java             # Order book entry
├── jmm/                               # Java Memory Model
│   └── MarketDataJMMDemo.java         # Visibility & happens-before
├── threads/                           # Thread Basics
│   └── OrderProcessorThreads.java     # Thread lifecycle & management
├── synchronization/                   # Synchronization Primitives
│   └── PortfolioSynchronization.java  # Locks, volatile, synchronized
├── coordination/                      # Thread Coordination
│   └── TradeSettlementCoordination.java # Coordination mechanisms
├── executors/                         # Executors & Thread Pools
│   └── OrderExecutionEngine.java      # Different executor types
├── collections/                       # Concurrent Collections
│   └── TradingConcurrentCollections.java # Thread-safe collections
├── async/                            # Async Programming
│   └── AsyncTradingOperations.java    # CompletableFuture patterns
├── patterns/                         # Concurrency Patterns
│   └── TradingConcurrencyPatterns.java # Design patterns
└── loom/                            # Project Loom
    └── HighFrequencyTradingLoom.java  # Virtual threads

🎮 Demo Modules

1. Java Memory Model (JMM)

• Stale reads - Market data visibility issues
• Volatile semantics - Ensuring visibility
• Happens-before relationships - Synchronization guarantees
• Thread.join() semantics - Coordination visibility

2. Thread Basics

• Thread creation methods - Different ways to create threads
• Thread states - Lifecycle demonstration
• Thread interruption - Proper cancellation handling
• Common pitfalls - What not to do

3. Synchronization Primitives

• synchronized methods/blocks - Mutual exclusion
• volatile variables - Visibility guarantees
• ReentrantLock - Advanced locking
• ReadWriteLock - Reader-writer scenarios
• StampedLock - Optimistic locking

4. Thread Coordination

• CountDownLatch - Waiting for task completion
• CyclicBarrier - Synchronizing at checkpoints
• Semaphore - Resource access control
• Phaser - Multi-phase coordination
• wait/notify - Legacy coordination

5. Executors & Thread Pools

• FixedThreadPool - Consistent capacity
• CachedThreadPool - Variable load
• SingleThreadExecutor - Sequential processing
• ScheduledThreadPool - Time-based execution
• Custom ThreadPoolExecutor - Advanced configuration
• ForkJoinPool - Work stealing

6. Concurrent Collections

• ConcurrentHashMap - Thread-safe maps
• CopyOnWriteArrayList - Read-optimized lists
• BlockingQueue variants - Producer-consumer queues
• ConcurrentLinkedQueue - Non-blocking queues
• DelayQueue - Time-delayed processing

7. Async Programming

• CompletableFuture creation - Async task creation
• Chaining operations - Pipeline building
• Combining futures - Parallel composition
• Exception handling - Error management
• Timeout handling - Time constraints

8. Concurrency Patterns

• Producer-Consumer - Order processing queues
• Work Stealing - Load balancing
• Future/Promise - Async result handling
• Actor Model - Message-based concurrency
• Immutable Objects - Thread safety by design
• Thread Pool Pattern - Custom implementations

9. Project Loom Virtual Threads

• Basic virtual threads - Lightweight thread creation
• Massive scalability - 10,000+ concurrent operations
• Performance comparison - Virtual vs platform threads
• Structured concurrency - Hierarchical task management
• Market data streaming - Real-time data processing
• Connection handling - Massive client simulation

🎯 Key Learning Outcomes

After running this demo, you'll understand:

• ✅ Java Memory Model - How threads see memory changes
• ✅ Synchronization - When and how to coordinate threads
• ✅ Thread Safety - Building correct concurrent code
• ✅ Performance - Choosing the right concurrency approach
• ✅ Scalability - Handling massive concurrent loads
• ✅ Best Practices - Industry-standard patterns
• ✅ Modern Java - Project Loom and virtual threads
• ✅ Real-world Application - Financial system scenarios

📊 Performance Insights

The demo includes performance comparisons showing:

• Virtual Threads vs Platform Threads - 3-5x improvement for I/O-intensive tasks
• Different Lock Types - Performance characteristics
• Concurrent Collections - Throughput under contention
• Async vs Sync - Latency and throughput differences

🔧 Configuration

The demo can be customized through:

• Thread pool sizes - Adjust for your system
• Task counts - Scale demonstrations up/down
• Simulation delays - Speed up/slow down operations
• Logging levels - Control output verbosity

🧪 Testing

# Run all tests
./gradlew test

# Run with verbose output
./gradlew test --info

📈 Production Considerations

This demo illustrates concepts you'll use in production systems:

• Risk Management - Concurrent position limits
• Order Processing - High-throughput order matching
• Market Data - Real-time price distribution
• Settlement - Multi-party coordination
• Reporting - Concurrent data aggregation
• Client Connections - Massive concurrent users

🤝 Contributing

This is an educational project demonstrating concurrency concepts. Feel free to:

• Add new trading scenarios
• Implement additional concurrency patterns
• Improve performance demonstrations
• Add more comprehensive examples

📚 Further Reading

• Java Concurrency in Practice
• Project Loom Documentation
• Java Memory Model Specification
• JEP 425: Virtual Threads

📝 License

This project is for educational purposes. Use the concepts and patterns in your own projects.

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Built with Java 21 • Project Loom • Gradle • ❤️