⚙️ Process vs Thread

Process A (PID 1234)          Process B (PID 5678)
┌──────────────────┐           ┌──────────────────┐
│  Code segment    │           │  Code segment    │
│  Data segment    │           │  Data segment    │
│  Heap            │           │  Heap            │
│  Stack           │           │  Stack           │
│  File handles    │           │  File handles    │
└──────────────────┘           └──────────────────┘
   Bộ nhớ RIÊNG                   Bộ nhớ RIÊNG
   ↑ CÁCH LY ↑                    ↑ CÁCH LY ↑

→ 2 processes KHÔNG chia sẻ bộ nhớ
→ Giao tiếp qua IPC (pipe, socket, shared memory)

// Node.js: Multi-process (cluster module)
const cluster = require('cluster');
const os = require('os');

if (cluster.isPrimary) {
    // Master process tạo workers
    const numCPUs = os.cpus().length;
    for (let i = 0; i < numCPUs; i++) {
        cluster.fork(); // Tạo child PROCESS (bộ nhớ riêng)
    }
    cluster.on('exit', (worker) => {
        console.log(`Worker ${worker.process.pid} died`);
        cluster.fork(); // Restart worker
    });
} else {
    // Worker process (mỗi worker = 1 process riêng)
    const express = require('express');
    const app = express();
    app.listen(3000);
}

Process (PID 1234)
┌──────────────────────────────────┐
│  Code segment    (SHARED)        │
│  Data segment    (SHARED)        │
│  Heap            (SHARED)        │
│                                  │
│  ┌─────────┐  ┌─────────┐      │
│  │ Thread 1│  │ Thread 2│      │
│  │ Stack 1 │  │ Stack 2 │      │
│  │ Reg. 1  │  │ Reg. 2  │      │
│  └─────────┘  └─────────┘      │
│                                  │
│  → Threads CHIA SẺ heap, code   │
│  → Mỗi thread có stack RIÊNG   │
└──────────────────────────────────┘

// Node.js: Worker Threads (chia sẻ bộ nhớ)
const { Worker, isMainThread, parentPort, workerData } = require('worker_threads');

if (isMainThread) {
    // Main thread
    const sharedBuffer = new SharedArrayBuffer(4); // Shared memory!

    const worker = new Worker(__filename, {
        workerData: { sharedBuffer }
    });

    worker.on('message', (msg) => console.log('Result:', msg));
} else {
    // Worker thread (chia sẻ memory với main thread)
    const { sharedBuffer } = workerData;
    const arr = new Int32Array(sharedBuffer);
    arr[0] = 42; // Ghi trực tiếp vào shared memory

    parentPort.postMessage('Done!');
}