Bayyana async models: callbacks, promises, async/await, da event loop.

Question

IT Interview Practice · Accepted Answer

**Waɗannan hanyoyi ne masu ci gaba da kyau don bayyana aikin non-blocking a kan thread ɗaya, dukansu ana motsa su a ƙarƙashi ta event loop da ke gudanar da callbacks da suke shirye ɗaya-ɗaya.** Suna sarrafa *lokacin* da lambar ke ci gaba, ba threads da yawa ba.

## Event loop

Madauki mai thread ɗaya yana riƙe queue na callbacks da suke shirye. Lokacin da aikin async (timer, I/O) ya ƙare, ana enqueue callback ɗinsa; madauki yana ɗauka na gaba yana gudanar da shi har ƙarshe, sannan yana maimaitawa. Babu abin da ke preempt callback da ke gudana, don haka aikin CPU mai tsawo yana toshe komai.

```text
[event loop] → run callback → I/O finishes → enqueue callback → run next → ...
```

## Salo uku

```js
// 1. Callbacks — nesting gets ugly ("callback hell")
readFile('a', (e, a) => readFile('b', (e, b) => done(a, b)));

// 2. Promises — chainable, flat error handling
readFile('a').then(a => readFile('b')).then(b => ...).catch(err => ...);

// 3. async/await — sequential-looking, still non-blocking
async function run() {
  const a = await readFile('a');   // yields to the loop while waiting
  const b = await readFile('b');
  return done(a, b);
}
```

`await` yana dakatar da function kuma yana mayar da iko ga event loop; lokacin da promise ya warware, aiwatarwa yana ci gaba inda ya tsaya. Syntactic sugar ne a kan promises — event loop ɗaya a ƙarƙashi.

## Me ya sa yake da muhimmanci

Wannan model yana ƙarfafa Node.js, browsers, da Python asyncio: babban I/O concurrency a kan thread ɗaya ba tare da sarkakiyar lock ba. Matsalar ita ce kada ka taɓa toshe loop — kira na synchronous mai CPU-nauyi ko blocking yana tsayar da kowane aikin da ke jira. Fahimtar cewa async ≠ parallel shine mai bambancewa gama-gari a hira.

Event loop

Salo uku

Me ya sa yake da muhimmanci

Tambayoyi masu alaƙa