Author: Zen and the Art of Computer Programming
1 Introduction
1.1 Asynchronous programming
In the information age, traditionally there is no distributed system architecture in a complete sense. Application servers are usually a centralized, centralized architecture, and applications communicate directly with each other, making it impossible to utilize multi-core CPU resources to achieve true parallel processing. Therefore, when the application needs to process user requests, it can only be executed in a serial manner, which is very inefficient. In order to solve this problem, new architectural models based on messaging, event-driven, and microservices have emerged, allowing single-machine applications to handle multiple tasks at the same time, improving the overall performance and throughput of the application. However, due to the asynchronous programming model, application developers need to have a deep understanding and design of application threads, coroutines, or processes to correctly handle asynchronous events.
1.2 Event Loop
In order to cope with the complexity of asynchronous programming, from the original callback function to the modern event-driven framework, the concept of event loop (event loop) has been introduced. It is an infinite loop that is used to continuously check whether there are pending events and timing. Converter, callback function, etc. Whenever an event occurs, it is added to the event queue, waiting to be scheduled to run. This event-driven programming model makes asynchronous programming very simple and easy to understand, allowing developers to focus on the application logic itself instead of getting caught up in complex asynchronous details.
1.3 Node.js event loop
The event loop of Node.js is a single-threaded model, which only allows one task to be executed at the same time. This ensures that the switching process between synchronous and asynchronous calls is controllable. Each event loop consists of 6 phases: Timers, Pending I/O callbacks, Idle, Poll, Close callbacks, and Check.
- Timers: Execute timer C