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High-Performance Multithreaded Web Server in C++\n\n[![Build Status](https://img.shields.io/badge/build-passing-brightgreen)](https://github.com/swe-robertkibet/multithreaded-webserver-cpp)\n[![C++17](https://img.shields.io/badge/C%2B%2B-17-blue)](https://github.com/swe-robertkibet/multithreaded-webserver-cpp)\n[![License](https://img.shields.io/badge/license-MIT-green)](https://github.com/swe-robertkibet/multithreaded-webserver-cpp/blob/main/LICENSE)\n[![Performance](https://img.shields.io/badge/performance-78.1K%20req%2Fs-brightgreen)](https://github.com/swe-robertkibet/multithreaded-webserver-cpp)\n\nA production-ready, high-performance HTTP web server implemented in modern C++17, featuring epoll-based event handling, thread pooling, intelligent caching, and comprehensive security features.\n\n## Performance Highlights\n\n- **78,091.55 requests/sec** peak performance with 1000 concurrent connections\n- **71,508.89 requests/sec** sustained throughput with 5000 concurrent connections\n- **47,831.58 requests/sec** average over 5-minute extended duration tests\n- **0% memory growth** under sustained load (excellent memory stability)\n- **Memory efficient** with exceptional stability (1.7MB stable memory usage)\n- **Production ready** with Docker containerization\n\n## Architecture\n\nThe multithreaded web server employs a sophisticated, layered architecture designed for high performance, scalability, and maintainability. The following diagrams illustrate the complete system design from different perspectives.\n\n### System Overview\n\nThis comprehensive diagram shows the complete request processing pipeline from client connection through response delivery, including all major components and their interactions.\n\n![Main Architecture](images/Main%20Architecture.png)\n\n_Complete system architecture showing the epoll-based event loop, thread pool management, request processing pipeline, embedded caching system, and configuration loading mechanism._\n\n### Component Layer Architecture\n\nThe system is organized into distinct layers, each with specific responsibilities and clear interfaces between components.\n\n![Architecture Components](images/Architecture%20Components.png)\n\n_Layer-based architecture view demonstrating the separation of concerns across Client Layer, Network Layer, Threading Layer, Application Layer, and Data Layer with actual component interactions._\n\n### Request Processing Flow\n\nThis detailed flowchart illustrates the complete request lifecycle with decision points, performance timings, and error handling paths.\n\n![Architecture Flow](images/Architecture%20Flow.png)\n\n_Actual request processing flow showing performance characteristics: ~0.1ms cache hits, ~0.5ms parsing, ~5-20ms file system operations, with real error handling and connection management implementation._\n\n### Core Components\n\n#### 1. **Event-Driven I/O (epoll)**\n\n- **Location**: `src/epoll_wrapper.cpp`, `include/epoll_wrapper.h`\n- Linux epoll for scalable I/O multiplexing\n- Non-blocking socket operations\n- Edge-triggered event notification\n- Handles thousands of concurrent connections efficiently\n\n#### 2. **Thread Pool Management**\n\n- **Location**: `include/thread_pool.h`\n- Custom thread pool implementation with task queue\n- Configurable worker thread count (auto-detects hardware threads)\n- Task queue with condition variable synchronization\n- Future-based task completion tracking\n\n#### 3. **HTTP Protocol Handler**\n\n- **Location**: `src/http_request.cpp`, `src/http_response.cpp`\n- Full HTTP/1.1 implementation\n- Keep-alive connection support\n- Comprehensive header parsing and validation\n\n#### 4. **Intelligent Caching System**\n\n- **Location**: `src/cache.cpp`, `include/cache.h`\n- LRU (Least Recently Used) eviction policy\n- TTL-based expiration (configurable)\n- Memory-efficient storage\n- Thread-safe with fine-grained locking\n\n#### 5. **Rate Limiting**\n\n- **Location**: `src/rate_limiter.cpp`, `include/rate_limiter.h`\n- Token bucket algorithm per client IP\n- Configurable requests per second and burst capacity\n- DDoS protection with automatic cleanup\n- Statistics tracking for monitoring\n\n#### 6. **File Handler**\n\n- **Location**: `src/file_handler.cpp`, `include/file_handler.h`\n- Static file serving with MIME type detection\n- Directory listing support\n- Efficient file streaming for large files\n- Security features (path traversal protection)\n\n#### 7. **Structured Logging**\n\n- **Location**: `src/logger.cpp`, `include/logger.h`\n- Separate access and error logs\n- Configurable log levels (DEBUG, INFO, WARN, ERROR)\n- Thread-safe logging with buffering\n- Apache Common Log Format compatible\n\n### Data Flow\n\n1. **Connection Acceptance**: Main thread accepts connections via epoll\n2. **Event Processing**: Events distributed to thread pool workers\n3. **Request Parsing**: HTTP request parsed and validated\n4. **Rate Limiting**: Check client IP against rate limits\n5. **Cache Lookup**: Check if requested resource is cached\n6. **File Processing**: Serve static files or generate dynamic content\n7. **Response Generation**: Build HTTP response with appropriate headers\n8. **Connection Management**: Handle keep-alive or close connection\n9. **Logging**: Record access and error information\n\n### Memory Management\n\n- **RAII Principles**: All resources managed with smart pointers\n- **Cache Management**: Automatic memory cleanup with LRU eviction\n\n## Features\n\n### Core Features\n\n- **High Performance**: 78K+ requests/sec with low latency\n- **Multithreaded**: Configurable thread pool with auto-scaling\n- **Event-Driven**: Linux epoll for efficient I/O multiplexing\n- **HTTP/1.1**: Full protocol support with keep-alive\n- **Static Files**: Efficient static content serving\n- **Caching**: Intelligent LRU cache with TTL\n- **Rate Limiting**: Token bucket per-IP rate limiting\n- **Logging**: Comprehensive access and error logging\n- **Configuration**: JSON-based runtime configuration\n\n### Security Features\n\n- **Path Traversal Protection**: Prevents directory escape attacks\n- **Rate Limiting**: DDoS protection with configurable limits\n- **Non-Root Execution**: Docker containers run as non-root user\n- **Input Validation**: Comprehensive HTTP request validation\n- **Resource Limits**: Configurable memory and connection limits\n\n### Operational Features\n\n- **Performance Monitoring**: Built-in metrics and statistics\n- **Docker Support**: Multi-stage builds for production\n- **Comprehensive Testing**: 600+ lines of unit tests\n- **Benchmarking**: Performance comparison tools included\n- **Configuration**: Runtime parameter adjustment\n\n## Quick Start\n\n### Prerequisites\n\n- C++17 compatible compiler (GCC 7+ or Clang 5+)\n- CMake 3.16+\n- Linux (Ubuntu 20.04+ recommended)\n\n### Build and Run\n\n```bash\n# Clone the repository\ngit clone https://github.com/swe-robertkibet/multithreaded-webserver-cpp.git\ncd multithreaded-webserver-cpp\n\n# Build the project\nmkdir build \u0026\u0026 cd build\ncmake .. -DCMAKE_BUILD_TYPE=Release\nmake -j$(nproc)\n\n# Run the server\n./bin/webserver 8080\n\n# Or with custom thread count\n./bin/webserver 8080 16\n```\n\n### Docker Deployment\n\n```bash\n# Build and run with Docker Compose\ndocker-compose up --build webserver\n\n# For development\ndocker-compose --profile development up webserver-dev\n\n# For performance testing\ndocker-compose --profile benchmark up\n```\n\n### Configuration\n\nEdit `config.json` to customize server behavior:\n\n```json\n{\n  \"server\": {\n    \"host\": \"0.0.0.0\",\n    \"port\": 8080,\n    \"max_connections\": 1000,\n    \"socket_timeout\": 30\n  },\n  \"threading\": {\n    \"thread_pool_size\": 8,\n    \"max_queue_size\": 10000\n  },\n  \"cache\": {\n    \"enabled\": true,\n    \"max_size_mb\": 100,\n    \"ttl_seconds\": 300\n  },\n  \"rate_limiting\": {\n    \"enabled\": true,\n    \"requests_per_second\": 100,\n    \"burst_size\": 200\n  }\n}\n```\n\n## Performance Benchmarks\n\n### Comprehensive Stress Test Results\n\n### Live Stress Test Demonstration\n\n![Stress Test Results](images/Stress%20Test.png)\n\n_Real-time stress testing demonstration showing the server handling high concurrent loads with excellent performance and resource efficiency._\n\n#### Connection Scalability Test\n\n| Concurrent Connections | Requests/sec  | Performance     |\n| ---------------------- | ------------- | --------------- |\n| 100                    | 39,565.85     | Baseline        |\n| 500                    | 55,934.55     | +41.4%          |\n| 1000                   | 78,091.55     | +97.3%          |\n| **2000**               | **73,075.56** | **+84.7% Peak** |\n| 5000                   | 71,508.89     | +80.7%          |\n\n#### Extended Duration Test\n\n| Test Duration | Avg Requests/sec | Stability  |\n| ------------- | ---------------- | ---------- |\n| 1 minute      | 46,706.94        | Stable     |\n| 5 minutes     | 47,831.58        | Consistent |\n| 10 minutes    | 48,858.91        | Sustained  |\n\n#### Memory Stability Test (5-minute sustained load)\n\n```\nInitial memory usage: 1,680KB\nFinal memory usage:   1,680KB\nMemory growth:        0% (0KB increase)\nMaximum memory:       1,680KB\nStatus:              No memory leaks detected\n```\n\n### Comparison with Industry Standards\n\n| Server          | Peak Requests/sec | Sustained Req/s | Memory Usage | Stability     |\n| --------------- | ----------------- | --------------- | ------------ | ------------- |\n| **This Server** | **78,091.55**     | **48,858.91**   | **1.7MB**    | **0% growth** |\n| Nginx           | ~45,000           | ~40,000         | ~25MB        | Stable        |\n| Apache          | ~25,000           | ~20,000         | ~100MB       | Variable      |\n\n**Performance Advantages:**\n\n- **73% faster** peak performance than Nginx\n- **212% faster** peak performance than Apache\n- **Exceptional memory efficiency** at 1.7MB (15x better than Nginx)\n- **Perfect memory stability** with zero growth under sustained load\n\n## Performance Optimization - Log Reduction Impact\n\n### High-Load Error Handling Optimization\n\nDuring stress testing, the server was producing excessive error logging for normal race condition scenarios that occur in high-concurrency environments. These logs were impacting performance by creating unnecessary I/O overhead.\n\n### Technical Background\n\nThe following error messages are **normal and expected** under high load in multithreaded scenarios:\n\n**Race Condition Errors:**\n\n- `[Response] fd=X ERROR: Connection already closed` (server.cpp:377)\n- `[Send] fd=X ERROR: Failed to send response: Bad file descriptor` (server.cpp:444)\n\n**Root Causes:**\n\n1. **Timing Issues**: Client disconnects while server is processing the response\n2. **Race Conditions**: Connection gets cleaned up by one thread while another thread tries to send data\n3. **High Load Behavior**: Under stress testing, clients timeout/disconnect before server can respond\n4. **Network Conditions**: High load causes natural connection drops\n\n**Why These Errors Are Normal:**\n\n- **High Concurrency**: With 10,000+ connection limit, more concurrent connections create more timing opportunities\n- **Client Behavior**: Load testing tools often timeout or close connections aggressively\n- **Network Stack**: TCP connections naturally drop under extreme load conditions\n- **Defensive Programming**: Server detects and handles these conditions gracefully instead of crashing\n\n### Optimization Impact\n\nBy removing these excessive log messages (while preserving all error handling logic), we achieved significant performance improvements:\n\n| Metric                | Before Optimization | After Optimization  | Improvement      |\n| --------------------- | ------------------- | ------------------- | ---------------- |\n| **Peak Performance**  | 72,158 req/s        | **78,091.55 req/s** | **+8.2%**        |\n| **1000 Connections**  | 58,267 req/s        | **78,091.55 req/s** | **+34.0%**       |\n| **Sustained (10min)** | 47,290 req/s        | **48,858.91 req/s** | **+3.3%**        |\n| **Memory Usage**      | ~18MB               | **1.7MB**           | **-91.1%**       |\n| **Log I/O Overhead**  | High                | **Eliminated**      | **100% reduced** |\n\n### Key Benefits\n\n**Performance Gain**: 8-34% improvement in request throughput  \n**Memory Efficiency**: 91% reduction in memory usage  \n**Clean Output**: Eliminated noise from expected connection drops  \n**Maintained Reliability**: All error handling logic preserved  \n**Production Ready**: Server handles edge cases silently and efficiently\n\n**Note**: This optimization demonstrates that high-performance servers must balance comprehensive logging with performance efficiency. The removed messages were debugging information for normal operational conditions, not actual errors requiring attention.\n\n## Testing\n\n### Unit Tests\n\n```bash\n# Build with tests\nmkdir build \u0026\u0026 cd build\ncmake .. -DBUILD_TESTS=ON\nmake -j$(nproc)\n\n# Run tests\n./webserver_tests\n```\n\n### Benchmark Testing\n\n```bash\n# Run comprehensive benchmarks\n./scripts/benchmark.sh\n\n# Quick performance test\n./scripts/quick_bench.sh\n\n# Stress test\n./scripts/stress_test.sh\n```\n\n## Project Structure\n\n```\nmultithreaded-webserver-cpp/\n├── include/           # Header files\n│   ├── server.h         # Main server class\n│   ├── thread_pool.h    # Thread pool implementation\n│   ├── http_request.h   # HTTP request parser\n│   ├── http_response.h  # HTTP response builder\n│   ├── cache.h          # LRU cache system\n│   ├── rate_limiter.h   # Rate limiting implementation\n│   ├── file_handler.h   # File serving logic\n│   ├── logger.h         # Logging system\n│   └── epoll_wrapper.h  # Epoll abstraction\n├── src/              # Source files\n│   ├── main.cpp         # Application entry point\n│   ├── server.cpp       # Server implementation\n│   ├── thread_pool.cpp  # Thread pool logic\n│   ├── http_request.cpp # Request parsing\n│   ├── http_response.cpp# Response generation\n│   ├── cache.cpp        # Cache implementation\n│   ├── rate_limiter.cpp # Rate limiting logic\n│   ├── file_handler.cpp # File operations\n│   ├── logger.cpp       # Logging implementation\n│   └── epoll_wrapper.cpp# Epoll wrapper\n├── tests/            # Unit tests (GoogleTest)\n├── scripts/          # Benchmarking scripts\n├── docker/           # Docker configuration\n├── public/           # Static web content\n├── logs/             # Server logs\n├── config.json          # Server configuration\n├── CMakeLists.txt       # Build configuration\n├── Dockerfile           # Multi-stage Docker build\n└── docker-compose.yml   # Container orchestration\n```\n\n## Configuration Options\n\n### Server Configuration\n\n- `host`: Bind address (default: \"0.0.0.0\")\n- `port`: Listen port (default: 8080)\n- `max_connections`: Maximum concurrent connections\n- `socket_timeout`: Connection timeout in seconds\n\n### Performance Tuning\n\n- `thread_pool_size`: Worker thread count (0 = auto-detect)\n- `max_queue_size`: Maximum task queue size\n- `cache.max_size_mb`: Cache memory limit\n- `cache.ttl_seconds`: Cache entry lifetime\n\n### Security Settings\n\n- `rate_limiting.enabled`: Enable/disable rate limiting\n- `rate_limiting.requests_per_second`: Request rate limit\n- `rate_limiting.burst_size`: Burst capacity\n\n## Contributing\n\n1. Fork the repository\n2. Create a feature branch: `git checkout -b feature/amazing-feature`\n3. Commit your changes: `git commit -m 'Add amazing feature'`\n4. Push to the branch: `git push origin feature/amazing-feature`\n5. Open a Pull Request\n\n### Development Setup\n\n```bash\n# Use development Docker container\ndocker-compose --profile development up webserver-dev\n\n# Or build locally with debug symbols\ncmake .. -DCMAKE_BUILD_TYPE=Debug -DBUILD_TESTS=ON\n```\n\n## Monitoring and Observability\n\n### Built-in Metrics\n\n- Request throughput (requests/sec)\n- Response time percentiles\n- Cache hit ratios\n- Rate limiting statistics\n- Active connection counts\n- Memory usage tracking\n\n### Log Analysis\n\n```bash\n# Monitor access logs\ntail -f logs/access.log\n\n# Check error logs\ntail -f logs/error.log\n\n# Analyze performance\ngrep \"200 OK\" logs/access.log | wc -l\n```\n\n## Troubleshooting\n\n### Common Issues\n\n**High CPU Usage**\n\n- Check thread pool size configuration\n- Monitor for busy loops in request processing\n- Verify epoll configuration\n\n**Memory Leaks**\n\n- Monitor cache size and eviction policies\n- Check for unclosed file descriptors\n- Use valgrind for detailed analysis\n\n**Connection Issues**\n\n- Verify firewall settings\n- Check file descriptor limits (`ulimit -n`)\n- Monitor connection timeout settings\n\n### Debug Mode\n\n```bash\n# Build with debug symbols\ncmake .. -DCMAKE_BUILD_TYPE=Debug\n\n# Run with debugging tools\ngdb ./webserver\nvalgrind --leak-check=full ./webserver\n```\n\n## License\n\nThis project is licensed under the MIT License - see the [LICENSE](https://github.com/swe-robertkibet/multithreaded-webserver-cpp/blob/main/LICENSE) file for details.\n\n## Acknowledgments\n\n- Linux epoll documentation and best practices\n- Modern C++ design patterns and idioms\n- HTTP/1.1 specification (RFC 7230-7235)\n- Performance optimization techniques from systems programming\n\n## Support\n\nFor issues and questions:\n\n- [Create an issue on GitHub](https://github.com/swe-robertkibet/multithreaded-webserver-cpp/issues)\n- Check existing documentation\n- Review performance benchmarks\n- Consult architecture diagrams\n\n---\n\n**Built with :heart: using modern C++17 and systems programming best practices.**\n","funding_links":[],"categories":[],"sub_categories":[],"project_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fswe-robertkibet%2Fmultithreaded-webserver-cpp","html_url":"https://awesome.ecosyste.ms/projects/github.com%2Fswe-robertkibet%2Fmultithreaded-webserver-cpp","lists_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fswe-robertkibet%2Fmultithreaded-webserver-cpp/lists"}