Libuv is a crucial component in Node.js, providing the core functionality for the non-blocking, event-driven architecture that Node.js is known for. Here's a detailed explanation of how libuv works under the hood:
Event-Driven Architecture
Libuv implements an event-driven architecture through its event loop. The event loop is the mechanism that allows Node.js to perform non-blocking I/O operations, despite JavaScript being single-threaded. When Node.js starts, it initializes the event loop, which is responsible for scheduling and executing tasks, handling events, and managing callbacks.
Event Loop Mechanics
The event loop in libuv operates by repeatedly checking for events and then processing them. Here’s a step-by-step breakdown of what happens during each tick of the event loop:
Poll for I/O: The event loop polls for I/O events using mechanisms like epoll, kqueue, or IOCP, depending on the operating system. It checks if there are any I/O operations that have completed and if any callbacks associated with those operations need to be executed[1].
Execute Timers: Timers set by setTimeout or setInterval are checked and executed if they are due[1].
Process I/O Callbacks: Callbacks from completed I/O operations are processed. This includes reading from disks, network requests, etc[1].
Set Immediate Callbacks: Callbacks scheduled with setImmediate are executed. These are callbacks that are supposed to be executed immediately after the I/O events[1].
Close Callbacks: Any close events, such as closing a file or a socket, are processed[1].
Thread Pool
For operations that are CPU-intensive or cannot be performed asynchronously at the OS level (like file system operations in Windows), libuv provides a thread pool. This thread pool can be used to offload tasks that would otherwise block the main event loop. The results of these operations are then returned to the event loop and their callbacks are executed asynchronously[1][5].
Handles and Requests
Libuv uses two primary data structures to manage I/O operations: handles and requests. Handles are long-lived objects representing resources like files, sockets, or timers. Requests represent individ...
