libuv: The C Library That Makes Node.js Fast

libuv is a cross-platform C library that powers Node.js's asynchronous I/O, handling network operations via OS kernel mechanisms and offloading file system and CPU-intensive tasks to a thread pool. The default thread pool size is 4, but developers can increase it up to 128 via the UV_THREADPOOL_SIZE environment variable. Understanding libuv helps developers avoid blocking the main thread with synchronous methods and optimize performance for production apps.