Libuv in Node.js

libuv is a high-performance, multi-platform library that powers Node.js by handling asynchronous I/O operations and managing its event-driven, non-blocking architecture. It abstracts system-level operations, allowing Node.js to efficiently perform I/O tasks across different operating systems.

Diagram illustrating the different parts that compose libuv and what subsystem they relate to:

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Key Roles of libuv in Node.js

  1. Event Loop Management – Implements the event loop, allowing Node.js to handle multiple asynchronous operations on a single thread.
  2. Thread Pool for Heavy Tasks – Uses a pool of worker threads for CPU-intensive tasks like file system operations, DNS lookups, and cryptographic functions. By default has 4 threads but can be changed.
  3. Cross-Platform Abstraction – Provides a unified API for different OS-specific system calls, making Node.js work seamlessly on Windows, macOS, and Linux.
  4. Handles Asynchronous I/O – Manages non-blocking I/O operations such as file reading, networking, and timers without blocking the main thread.
  5. Supports Sockets and Networking – Enables TCP, UDP, and other network communication for server applications.
  6. Timers & Signals – Implements setTimeout, setInterval, and other system event handlers efficiently.

Why libuv Matters?

Without libuv, Node.js wouldn't be able to efficiently handle concurrency. It allows Node.js to appear single-threaded while performing multi-threaded operations behind the scenes, making it powerful for building scalable, high-performance applications.

Handles and Requests in libuv

In libuv, handles and requests are core components that enable efficient asynchronous I/O operations.

1. Handles (Persistent Operations)

Handles represent long-lived resources that stay active for multiple events, such as open network sockets or timers. They are tied to the event loop and continuously listen for events.

Examples of Handles in libuv: