What Are the Different I/O Models and When Should You Use Them?

Understanding I/O Models

Before diving into code, it is useful to know the four classic I/O models:

1. Synchronous Blocking I/O (Blocking I/O) : The traditional model where a read or write call blocks the executing thread until the operation completes.

2. Synchronous Non‑Blocking I/O (Non‑blocking I/O) : Sockets are created in blocking mode by default; non‑blocking I/O requires explicitly setting the socket to NONBLOCK. Note that the term “NIO” here does not refer to Java’s New I/O library.

3. I/O Multiplexing (Reactor pattern) : Often called asynchronous blocking I/O. It uses a single thread to monitor multiple file descriptors (e.g., select, epoll, Java Selector) and dispatches events when data is ready. This is why Redis, a single‑threaded server, can achieve high throughput.

4. Asynchronous I/O (Proactor pattern) : Known as asynchronous non‑blocking I/O. The operating system completes the I/O operation and notifies the application via callbacks or completion ports.

Diagram

After reviewing these concepts, you should have a clearer picture of how each I/O model works and be able to choose the most suitable one for your application.