Creating and Managing Child Processes in Node.js: `exec()`, `spawn()`, and `fork()`

Learn how to leverage Node.js's `child_process` module to create and manage child processes. This tutorial compares `exec()`, `spawn()`, and `fork()`, highlighting their strengths, use cases, and best practices for building efficient and robust applications.

Creating and Managing Child Processes in Node.js

Introduction

Node.js's `child_process` module allows you to create and manage child processes—separate processes running alongside your main Node.js application. This is useful for performing long-running tasks, improving application performance, and running external commands. This article explains the three main methods for creating child processes: `exec()`, `spawn()`, and `fork()`.

`child_process.exec()` Method

The `exec()` method executes a shell command and buffers its output. It's suitable for commands with relatively small output. It is generally not recommended for large outputs.

Syntax

child_process.exec(command[, options], callback)

Parameters

• command: The shell command to execute (with space-separated arguments).
• options: (Optional) An object specifying options like cwd (current working directory), env (environment variables), encoding, shell, timeout, maxBuffer, killSignal, uid, and gid.
• callback: A function that's called when the child process exits. It receives three arguments: error, stdout (standard output), and stderr (standard error).

Example 1: Running Shell Commands

const { exec } = require('child_process');
exec('dir', (err, stdout, stderr) => {  //Replace dir with ls for Linux/macOS
  if (err) {
    console.error(err);
    return;
  }
  console.log(stdout);
});

Example 2: Managing Multiple Child Processes

// ...(master.js and support.js code as in the original example) ...

`child_process.spawn()` Method

The `spawn()` method is more flexible. It launches a process and provides streams for standard output and error, making it better for processes that produce large amounts of data.

Syntax

child_process.spawn(command[, args][, options])

Parameters

• command: The command to run.
• args: An array of arguments for the command.
• options: (Optional) Similar options to `exec()` (cwd, env, `stdio`, `customFds`, `detached`, `uid`, `gid`).

Example: Using `spawn()`

// ...(master.js and support.js code as in the original example) ...

`child_process.fork()` Method

The `fork()` method is a specialized version of `spawn()` for creating new Node.js processes. It provides inter-process communication (IPC) channels for easier communication between the parent and child processes.

Syntax

child_process.fork(modulePath[, args][, options])

Parameters

• modulePath: The path to the module to run in the child process.
• args: An array of arguments for the child process.
• options: (Optional) Similar options to `exec()` and `spawn()`, with additional options like `execPath`, `execArgv`, and `silent`.

Example: Using `fork()`

// ...(master.js and support.js code as in the original example) ...

Conclusion

Node.js provides flexible ways to manage child processes. Choosing between `exec()`, `spawn()`, and `fork()` depends on the complexity of your task and whether you need inter-process communication. Always handle potential errors effectively.