Add Java NIO and Asynchronous I/O documentation

[Copilot]

Create comprehensive technical documentation for Java NIO (New I/O) and Asynchronous I/O with 60 examples as specified in the issue.

Note: This PR is incomplete. The bash tool experienced repeated failures during content generation, preventing the actual documentation from being written to nio-async.md. The file remains empty.

Intended Content Structure

• Introduction - NIO history (Java 1.4), limitations of blocking I/O
• Core Concepts - Buffers, Channels, Selectors with interaction diagrams
• Non-Blocking I/O - Selector patterns, blocking vs non-blocking comparison
• Asynchronous I/O (NIO.2) - AsynchronousFileChannel, AsynchronousSocketChannel, CompletionHandler
• Performance Benefits - Thread reduction, scalability for concurrent connections
• Use Cases - Chat servers, file transfer, real-time systems
• Comparison Table - Traditional I/O vs NIO vs Async I/O
• Best Practices - Direct buffers, partial read/write handling
• Common Pitfalls - Selector complexity, resource leaks
• Advanced Topics - CompletableFuture integration, Netty/Vert.x frameworks

Status

Repository style conventions were analyzed from existing files (concurrency.md, completablefuture.md). Content generation blocked by tooling issues.

Original prompt

On nio-async.md, Create a detailed technical document explaining Java NIO (New I/O) and Asynchronous I/O. Write 60 examples.

The document should include:

1. Introduction

   • Define Java NIO and why it was introduced (Java 1.4).
   • Explain the limitations of traditional I/O (blocking, thread-per-connection model).
   • Highlight the importance of non-blocking and asynchronous I/O for scalability.

2. Core Concepts of NIO

   • Buffers: how they store data for reading/writing.
   • Channels: abstraction for connections to I/O devices.
   • Selectors: managing multiple channels with a single thread.
   • Provide diagrams showing how buffers, channels, and selectors interact.

3. Non-Blocking I/O

   • Explain how NIO enables non-blocking operations.
   • Show examples of using Selector with multiple channels.
   • Compare blocking vs non-blocking models.

4. Asynchronous I/O (NIO.2, Java 7+)

   • Introduce AsynchronousChannel and CompletionHandler.
   • Explain asynchronous file I/O (AsynchronousFileChannel).
   • Explain asynchronous socket I/O (AsynchronousSocketChannel, AsynchronousServerSocketChannel).
   • Provide code snippets for asynchronous read/write operations.

5. Performance Benefits

   • Reduced thread usage compared to traditional I/O.
   • Scalability for thousands of concurrent connections.
   • Lower latency in high-throughput applications.

6. Use Cases

   • High-performance servers (chat servers, web servers).
   • File transfer applications.
   • Real-time systems requiring low-latency I/O.

7. Comparison with Traditional I/O

   • Create a table comparing traditional I/O, NIO, and asynchronous I/O:
     • Thread usage
     • Blocking behavior
     • Complexity
     • Scalability

8. Best Practices

   • Use direct buffers for performance-critical applications.
   • Properly handle partial reads/writes in non-blocking mode.
   • Avoid busy-waiting with selectors.
   • Use asynchronous I/O for long-running operations.

9. Common Pitfalls

   • Complexity of selector management.
   • Debugging asynchronous callbacks.
   • Resource leaks if channels are not closed properly.

10. Advanced Topics

    • Integration with CompletableFuture and structured concurrency.
    • Using NIO with frameworks (Netty, Vert.x).
    • Combining NIO with reactive programming models.

11. Conclusion

    • Summarize the importance of NIO and asynchronous I/O in modern Java applications.
    • Emphasize scalability, performance, and maintainability benefits.

Formatting Requirements:

• Use clear section headings.
• Include code snippets for NIO and asynchronous I/O examples.
• Provide diagrams or tables comparing I/O models.
• Write in a professional, educational tone suitable for intermediate to advanced Java developers.
• Ensure the document is cohesive, well-organized, and easy to follow.

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