15. Worker Threads (worker_threads) & SharedArrayBuffer for CPU-Bound Tasks • Node.js Backend Architecture: Libuv to High-Scale Microservices • Rishabh Ki Kaksha

*   **Cluster Module:** Multiple **OS Processes** (Heavyweight, isolated memory, 30MB+ RAM per process).
*   **Worker Threads (`worker_threads`):** Multiple **Threads in 1 single Process** (Lightweight, share same V8 process memory, zero-copy data transfer).

**When to Use Worker Threads:**
> Heavy CPU-bound tasks (Image resizing with Sharp, AI tensor calculation, massive JSON parsing, cryptography).

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### 2. Worker Threads Implementation with `parentPort`

```javascript
// main.js
const { Worker } = require('worker_threads');

// Server remains 100% responsive while heavy math runs in background thread!
app.get('/heavy-calc', async (req, res) => {
    const result = await runFibonacciWorker(45);
    res.json({ result });
});

// fib_worker.js
const { workerData, parentPort } = require('worker_threads');

function fib(n) {
    return n <= 1 ? n : fib(n - 1) + fib(n - 2);
}

const answer = fib(workerData.num);
parentPort.postMessage(answer);
```

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### 3. Zero-Copy Shared Memory with `SharedArrayBuffer` & `Atomics` ⚡

Data ko serialize/deserialize kiye bina threads ke beech shared memory chunk pass karna:

```javascript
// Shared 1024-byte buffer across main thread and worker threads
const sharedBuffer = new SharedArrayBuffer(1024);
const sharedArray = new Int32Array(sharedBuffer);

// Thread-safe atomic operations:
Atomics.add(sharedArray, 0, 10);
Atomics.wait(sharedArray, 0, 0); // Sleeps thread until notified!
```

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### 4. Master Comparison Matrix

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### 5. Interview Ke 3 Sawal Is Topic Se

1. **`postMessage()` worker threads me data kaise transfer karta hai?** -> Default me HTML5 Structured Clone Algorithm use karke data copy karta hai; agar `Transferable` objects (jaise `ArrayBuffer`) pass karein toh ownership transfer ho jaati hai (Zero Copy).
2. **`Atomics` object ki zaroorat kyu padti hai `SharedArrayBuffer` ke sath?** -> Race Conditions aur data corruption ko rokne ke liye taaki multiple threads ek hi memory index ko safely read/write kar sakein.
3. **Piscina library kya hai?** -> Production-grade Worker Thread Pool library jo thread reuse aur task queueing manage karti hai bina har request par naya thread spawn kiye.

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**Next Topic:** 16. Real-Time WebSockets Architecture: Socket.io with Redis Adapter Scaling

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Rishabh Gehlot

PHP 8+ & Laravel 11 Master Track