Is nodejs multi-threaded or single-threaded?

Node.js multi-threaded or single-threaded?

In the development world, Node.js residents are often asked this question: Is Node.js multi-threaded or single-threaded? Let’s find out.

Node.js is an open source, cross-platform JavaScript runtime environment built on the Chrome V8 engine. The main features of Node.js are single-threaded, non-blocking I/O processing, and event-driven. The single thread of Node.js mainly means that the main thread is single-threaded, but behind it is a process-like underlying mechanism that can execute multiple child threads at the same time, achieving a certain multi-threading effect.

First let’s talk about “single thread”. Node.js runs in a single thread. In fact, the single thread here does not mean that the Node.js runtime is single-threaded, but that there is only one V8 instance executing JavaScript code in the Node.js process. However, Node.js has an event loop mechanism that sends I/O events to be processed outside the system kernel to perform non-blocking I/O. The code is executed in the callback function, so the entire program will appear to be multi-threaded, so many people will think that Node.js is multi-threaded, which is actually a misunderstanding.

So, why does Node.js adopt a single-threaded model?

First of all, the JavaScript language itself is single-threaded. This is determined by the characteristics of the language itself and is not the result of a random choice. Since JavaScript only provides a single thread, it can avoid problems such as deadlock and state synchronization. It does not have to pay attention to the modification of state variables at any time like multi-threaded programming. Therefore, the code is simplified and the execution environment is safer. In other words, the reason why Node.js adopts a single-threaded model is to better utilize the characteristics of JavaScript.

Secondly, the biggest feature of Node.js is that it is event-driven and handles requests through the event loop. This model is very beneficial for high-concurrency scenarios and I/O-intensive scenarios, and can achieve higher efficiency. The single-threaded model can coordinate multiple client requests, making the program more flexible and reducing the complexity of the entire system. Because thread concurrency has problems such as locks and competition, it cannot be as simple as a single-thread. This feature makes Node. js is excellent at handling high-concurrency, large-traffic, and scalable services.

Thirdly, the single-threaded model of Node.js reduces the process overhead. Compared with multi-threading, single-threading eliminates a series of overheads such as multi-threaded context switching. Although the underlying layer of Node.js still uses multi-threaded kernel technology during actual execution, developers only need to focus on writing JavaScript code.

If we must say that Node.js is multi-threaded, then we can say that Node.js itself has only one main thread, but several threads will be automatically created when performing some tasks. Node.js uses multi-threading in its underlying implementation, such as I/O threads, which are responsible for multiple worker threads such as reading data and processing data. However, the running of these threads is all handled internally by Node.js. For JavaScript developers, they are invisible and do not require attention.

There is also a model in Node.js called Cluster, which can create multiple child processes through the main process to listen to the same port to achieve load balancing between processes. In this way, each sub-process can take full advantage of the multi-core CPU, thereby improving the concurrency capabilities of the entire program. However, the Cluster module is not a core module of Node.js. Developers can manually create child processes by calling the child_process.fork() method to implement multiple processes.

So, Node.js is a single-threaded model, but it inherently has multi-threaded effects. The single-threaded model of Node.js is very flexible, can handle a large number of requests, and has good scalability. Only when we need to perform some tasks that take a long time to calculate, we need to use the multi-threading model.

Finally, when using Node.js, we need to learn how to take advantage of the asynchronous and non-blocking features it provides to achieve higher concurrency and shorter response time.

To summarize, Node.js is an event-driven, non-blocking I/O single-threaded model. This model has higher efficiency, better scalability, and less complexity. Better resource utilization efficiency. However, if there are computationally intensive tasks that need to be executed, you need to adopt the multi-threading model or use the child_process.fork() method provided by Node.js to manually create a child process.

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