hardSystem Design

What is the role of `libuv` in Node.js?

Q: What is the role of `libuv` in Node.js?

**TL;DR.** **libuv** is the C library that gives Node its **event loop**, its **thread pool**, and cross-platform **async I/O**. It abstracts OS primitives (epoll on Linux, kqueue on macOS, IOCP on Windows) and offloads work that has no async OS API onto a small thread pool — this is what makes single-threaded Node non-blocking. Event loop OS async I/O epoll / kqueue / IOCP (network) <rec

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libuvarchitectureevent loopi/o

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The thread pool is shared — size it for crypto/fs heavy apps

# 4 parallel pbkdf2 hashes saturate the default pool of 4 threads;
# a 5th waits. Raise the pool so they run together:
UV_THREADPOOL_SIZE=8 node server.js

# Network sockets do NOT use the pool (they use epoll/kqueue/IOCP),
# so this mainly helps fs, dns.lookup, crypto, and zlib workloads.

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