How to Launch Child Processes in Node.js

How to Launch Child Processes in Node.js

In this tutorial, you will create child processes while executing a series of sample Node.js applications. You’ll create processes with the child_process module by retrieving the results of a child process via a buffer or string with the exec() function, and then from a data stream with the spawn() function. You’ll finish by using fork() to create a child process of another Node.js program that you can communicate with as it’s running. To illustrate these concepts, you will write a program to list the contents of a directory, a program to find files, and a web server with multiple endpoints.

Introduction

When a user executes a single Node.js program, it runs as a single operating system (OS) process that represents the instance of the program running. Within that process, Node.js executes programs on a single thread. As mentioned earlier in this series with the How To Write Asynchronous Code in Node.js tutorial, because only one thread can run on one process, operations that take a long time to execute in JavaScript can block the Node.js thread and delay the execution of other code. A key strategy to work around this problem is to launch a child process, or a process created by another process, when faced with long-running tasks. When a new process is launched, the operating system can employ multiprocessing techniques to ensure that the main Node.js process and the additional child process run concurrently, or at the same time.

Node.js includes the child_process module, which has functions to create new processes. Aside from dealing with long-running tasks, this module can also interface with the OS and run shell commands. System administrators can use Node.js to run shell commands to structure and maintain their operations as a Node.js module instead of shell scripts.

In this tutorial, you will create child processes while executing a series of sample Node.js applications. You’ll create processes with the child_process module by retrieving the results of a child process via a buffer or string with the exec() function, and then from a data stream with the spawn() function. You’ll finish by using fork() to create a child process of another Node.js program that you can communicate with as it’s running. To illustrate these concepts, you will write a program to list the contents of a directory, a program to find files, and a web server with multiple endpoints.

Prerequisites

  • You must have Node.js installed to run through these examples. This tutorial uses version 10.22.0. To install this on macOS or Ubuntu 18.04, follow the steps in How To Install Node.js and Create a Local Development Environment on macOS or the Installing Using a PPA section of How To Install Node.js on Ubuntu 18.04.
  • This article uses an example that creates a web server to explain how the fork() function works. To get familiar with creating web servers, you can read our guide on How To Create a Web Server in Node.js with the HTTP Module.

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