Libuv Thread Pool & Concurrency Lab

Interactive evaluation of UV_THREADPOOL_SIZE worker thread dispatching, multi-process clustering, and worker threads.

Libuv Thread Architecture

UV_THREADPOOL_SIZE & Asynchronous Worker Offloading

UV_THREADPOOL_SIZE = 4

V8 Main Thread (Single JS Stack)100% Non-Blocking

Executes all your JavaScript code. When asynchronous fs, crypto, or zlib functions are called, V8 offloads the synchronous blocking C syscall to Libuv and immediately returns.

Main Thread Status: FREE ⚡

Accepting incoming HTTP sockets on epoll...

Libuv Thread Pool (C/C++ Workers)4 Threads

Thread #1

💤 IDLE

Thread #2

💤 IDLE

Thread #3

⚡ RUNNING

Thread #4

⚡ RUNNING

Thread Pool Log: Click "Dispatch 4 Heavy Crypto Tasks" to simulate thread saturation.

Multi-Core Scale Architectures

Node.js Clustering vs Worker Threads

Multi-Process vs Multi-Thread

Architecture Diagram:cluster

Primary Master Process (PID: 1000) [Port 3000 IPC Router]

Worker #1 (PID: 1001)
Isolated 64MB RAM

Worker #2 (PID: 1002)
Isolated 64MB RAM

When to Use Which:

Clustering: Web Server Throughput

Ideal for web applications (Express, Fastify, NestJS) where each process independently handles non-blocking HTTP requests across all CPU cores.

Memory Sharing: ❌ No (Use Redis for sessions)