How Nginx Rewrite Blocks IE and the Five Core Server I/O Models Explained

nginx rewrite to block IE browsers

1. Four theoretical I/O models

Caller (service process): Blocking – the process is suspended until I/O completes; Non‑blocking – the process can continue other work while I/O is pending.

Called function (system I/O read/write): Synchronous – the function does not return until the operation finishes; Asynchronous – the function returns immediately with an unfinished status and notifies the caller upon completion.

Four theoretical models:

Synchronous blocking

Synchronous non‑blocking (rarely used)

Asynchronous blocking

Asynchronous non‑blocking: true asynchronous I/O

2. Five I/O models in network services

1) Synchronous blocking model

Worker process calls an I/O library function and is blocked until the first stage (data loaded from disk to kernel space) finishes; then it remains blocked while the kernel copies data to user space.

2) I/O multiplexing (synchronous blocking model)

Uses select() or poll() to manage multiple I/O requests; the worker blocks on the multiplexing call but can handle many descriptors simultaneously, improving efficiency. The second stage still requires copying data to user space and remains blocked.

3) Synchronous non‑blocking (busy‑wait model)

Worker calls an I/O function, can do other work while periodically checking if I/O is complete; the second stage still involves copying data to user space and blocks.

4) Event‑driven model (synchronous non‑blocking)

Worker calls an I/O function and does not wait; the kernel notifies the process via events (e.g., epoll(), kqueue()) when I/O completes. The second stage still blocks during data copy.

5) Fully asynchronous (AIO)

Full async 1: Worker calls an I/O function, does not wait; kernel notifies completion, and the library copies data to user space without worker involvement.

Full async 2: Similar, but data is transferred via memory mapping (mmap) instead of copying.

Implementation can use the libevent library.