Non-blocking I/O in Node.js: Underlying Principles for High-Concurrency Scenarios

This article focuses on explaining Node.js non-blocking I/O and its advantages. Traditional synchronous blocking I/O causes programs to wait for I/O completion, leaving the CPU idle and resulting in extremely low efficiency under high concurrency. Non-blocking I/O, by contrast, initiates a request without waiting, immediately executing other tasks, and notifies completion through callback functions, which are uniformly scheduled by the event loop. Node.js implements non-blocking I/O through the event loop and the libuv library: asynchronous I/O requests are handed over to the kernel (e.g., Linux epoll) by libuv. The kernel monitors I/O completion status, and upon completion, the corresponding callback is added to the task queue. The main thread is not blocked and can continue processing other tasks. Its high concurrency capability arises from: a single-threaded JS engine that does not block, with a large number of I/O requests waiting concurrently. The total time consumed is only the average time per single request, not the sum. libuv abstracts cross-platform I/O models and maintains an event loop (handling microtasks, macrotasks, and I/O callbacks) to uniformly schedule callbacks. Non-blocking I/O enables Node.js to excel in scenarios such as web servers, real-time communication, and I/O-intensive data processing. It is the core of Node.js's high concurrency handling, efficiently supporting tasks like front-end engineering and API services.