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🧩 Event Loop Based Structure

✅ Overview​

A structural style where one (or few) event loops process asynchronous I/O and callbacks/handlers in order. Representative in Node.js and browser JavaScript execution environments.

✅ Problems Addressed​

  • Scalability limit of synchronous I/O model creating threads per request.
  • Thread context switch and lock costs.
  • Handling massive connections (C10K problem, etc.).

Event Loop model realizes high throughput by:

"Handling many connections with asynchronous I/O and event loop instead of increasing threads."

✅ Basic Philosophy & Rules​

● Event Loop​

  • Loop that takes events one by one from the event queue and executes corresponding handlers.

● Asynchronous I/O​

  • I/O operations (Network, File, etc.) are issued asynchronously.
  • Event is stacked in queue upon completion, and processed in the next loop.

● Single Thread Model (Often)​

  • Design that minimizes use of locks and shared memory.
  • Expresses asynchrony with Callback / Promise / async/await instead.

✅ Suitable Applications​

  • Web servers handling many client connections.
  • Chat / Game / Real-time Web apps.
  • Lightweight API servers.

Features:

  • Strong in I/O bound processing.
  • Low memory consumption, easy to scale with few threads.

❌ Unsuitable Cases​

  • Apps containing many CPU bound heavy calculations.
  • Long blocking processing (blocks the loop).

Such processing needs to be escaped to workers (separate threads/processes).

✅ History (Genealogy / Parent Styles)​

  • Development from GUI event loop (main thread).
  • Combined with asynchronous I/O models (epoll, kqueue, etc.) to server side.
  • Widely spread with event-driven server platforms like Node.js.

✅ Related Styles​

✅ Representative Frameworks​

Event Loop based structure is widely adopted in platforms centered on asynchronous I/O.

  • Node.js
    Most representative Event Loop implementation. Single thread + Asynchronous I/O model is core.

  • Browser (JavaScript Runtime)
    setTimeout / Promise / fetch etc. all operate on Event Loop.

  • Deno / Bun (JavaScript Runtime)
    Adopts event loop model similar to Node.js.

  • High Performance Servers like Nginx / Envoy
    Realize high throughput by event loop + asynchronous I/O inside core.

✅ Design Patterns Supporting This Style​

Event Loop itself is a low-level execution model, but strongly linked with the following patterns.

  • Observer
    Basic of notification model: Event firing → Handler execution.

  • Command
    Used when treating asynchronous callbacks or processing as "operation objects".

  • Mediator
    Sometimes used as a mechanism to coordinate multiple events/handlers.

  • Iterator
    Useful when processing asynchronous streams sequentially (AsyncIterator etc.).

✅ Summary​

Event Loop based structure is a style realizing high throughput with simple ideas:

  • Asynchronous I/O
  • Event Queue
  • Single (or few) Loops

It is good to consider as one of the "default candidates" when designing I/O bound servers.