A complete guide to the Node.js event loop - A deeper understanding of the event loop in Node.js will allow you to enhance its performance according to your project's needs.
Originally published by Piero Borrelli at blog.logrocket.com
Let’s try to address the first part. The easiest way for me to answer such a question would be by listing out many definitions of what Node technically is:
That is really what mutated it into a must-have for every web developer out there.
Understanding exactly how Node works behind the scenes will not only generate a greater knowledge of this technology, but it will also create traction for the people out there who haven’t used it to actually dive in and start learning it.
And for all the people out there who are already professionals in this field, understanding the in and outs of it will turn you into a new, up-to-date developer fully equipped to enhance its performance based on your needs.
So, in order to excavate into the world of Node, we will examine its core part: the event loop, which, in fact, is the part responsible for its non-blocking I/O model.
Before diving deep into the event loop, I would like to spend some time on threads. If you are wondering why this is necessary, I will tell you that in order to better understand a concept, we must first start to form a vocabulary in our minds that will help us to recognize each part of a system. This will eventually be of great advantage when later reading about the event loop, how it works, and how the concept of a thread applies to it.
Whenever we run a program, we create an instance of it, and, associated with that instance, we have something internal called threads. A thread can be seen as a unit of operations that our CPU has to perform for us. Many different threads can be associated with a single process of a program. Here is a graphic to help you form this idea in your mind:
A simple graphic on threads.
The most important piece to understand when talking about threads is: How can our machine determine which thread to process at any given moment in time?
As we know, our machines have a limited amount of resources (CPU, RAM), so it’s very important to correctly determine where we are going to allocate them or, better, which operations take precedence over others. And this all has to happen while still ensuring that no one operation takes too much time — nobody likes a slow laptop.
The mechanism used to solve the allocation problem is called scheduling, and it’s managed by our operating system by an entity called the OS scheduler. The logic behind this can be very complex, but to make a long story short, we can group two of the biggest ways in which this operation is performed:
How multi-core machines process threads.
Now that we have got a healthy refresh on how threads work, we can finally tackle the Node.js event loop logic. By reading this, you will understand the reason behind the previous explanation, and every piece will go at the right spot by itself.
Whenever we run a Node program, a thread is automatically created. This thread is the only place where our entire codebase is going to be executed. Inside of it, something called the event loop is generated. The role of this loop is to schedule which operations our only thread should be performing at any given point in time.
Please note: the event loop doesn’t get generated instantly as soon as we run our program. In fact, it only runs once the whole program has been executed.
Let’s now try to simulate how the event loop works and what it does to make our program work. To do this, I’m going to pretend that I’m feeding Node with a file called
myProgram and then get into the details of what the event loop will do with it.
In particular, I’m going to first write a brief little graphical explanation of what is happening during any event loop tick, and then I’m going to explore these phases in a deeper way.
A graphical explanation of the event loop.
I shouldn’t need to tell you the event loop is, in fact, a loop. This means it has a specific condition that will determine if the loop needs to iterate again or not. Every iteration of the event loop is called a tick.
Whenever we execute our program, we will have a series of operations that need to be performed. These operations can be split into three main types:
We will go into more details on these later; for now, let’s just remember that whenever one of these operations is pending, the event loop will perform a new tick.
For every loop iteration, we can distinguish the following phases:
setInterval()are ready to be called in case of an expired timer.
setImmediate()function are ready to be called.
This is a very common misconception about this technology. Node runs on a single thread, but some of the functions included in the Node.js standard library do not (the
fs module functions, for example ); their logic runs outside of the Node.js single thread. This is done in order to preserve our programs’ speed and performance.
When using Node.js, a special library module called libuv is used to perform async operations. This library is also used, together with the back logic of Node, to manage a special thread pool called the libuv thread pool.
This thread pool is composed of four threads used to delegate operations that are too heavy for the event loop. The above-mentioned long-running tasks in the event loop logic represent those operations described here as too expensive for the event loop.
In that sense, while some stack-like structures are involved in the above-mentioned process, a more precise answer would be that the event loop is composed of a series of phases, each with its own specific tasks, all processed in a circular repetitive way. For more info about the event loop’s exact structure.
Understanding the event loop is a vital part of using Node.js, whether you are trying to get more insights about this technology, learn how to improve its performance, or find a new, interesting reason to learn a new tool.
This guide should have helped you in exploring this subject. Feel free to leave a comment down below, opinions and feedbacks are extremely useful to help everybody to learn better.
Originally published by Piero Borrelli at blog.logrocket.com
We are providing robust Node.JS Development Services with expert Node.js Developers. Get affordable Node.JS Web Development services from Skenix Infotech.
A Guide to Hire Node.js Developers who can help you create fast and efficient web applications. Also, know how much does it cost to hire Node.js Developers.
A thoroughly researched list of top NodeJS development companies with ratings & reviews to help hire the best Node.JS developers who provide development services and solutions across the world. List of Leading Node.js development Service Providers...
Looking for an attractive & user-friendly web developer? HourlyDeveloper.io, a leading web, and mobile app development company, offers web developers for hire through flexible engagement models. You can **[Hire Web...