What Are Processes and Threads? How to Start a Process in Node.js and Implement Inter-Process Communication

In computer science, processes and threads are two key concepts. They are the basic units of execution managed by the operating system, essential for understanding program concurrency and resource management. This article provides an in-depth explanation of processes and threads, their differences, and how to create processes and implement inter-process communication in Node.js.

What Is a Process?

A process is the basic unit of resource allocation in the operating system. Each process is an instance of a running program with its own memory space, data stack, and other system resources such as file handles and network connections. Because processes are independent of each other, a crash or exit of one process does not affect others.

• Memory Space: Each process has its own address space and does not share memory with other processes, reducing interference and security issues.
• Resource Management: The operating system allocates necessary resources to each process, such as CPU time, memory, and file handles.
• Isolation: Processes are independent of each other; an error in one process usually does not affect others.

What Is a Thread?

A thread is an execution path within a process. A process can contain multiple threads, which share the process’s resources (such as memory space and file handles) but have their own stack space and program counter.

• Shared Resources: Threads within the same process share resources, making communication between threads faster and less costly.
• Lightweight: Creating, destroying, and switching between threads is less costly than doing so with processes.
• Concurrent Execution: Multiple threads can run concurrently on multi-core CPUs, improving program execution efficiency.

Differences Between Processes and Threads

How to Start a Process in Node.js?

Node.js provides various ways to create and manage processes, with the child_process module being the most common. This module allows you to create child processes and perform inter-process communication. Here are some common methods:

1. exec

exec is used to execute a shell command and return the command’s output via a callback function, suitable for short-running processes.

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const { exec } = require("child_process");
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exec("ls -l", (error, stdout, stderr) => {
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  if (error) {
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    console.error(`Error: ${error.message}`);
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    return;
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  }
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  if (stderr) {
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    console.error(`Stderr: ${stderr}`);
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    return;
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  }
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  console.log(`Stdout: ${stdout}`);
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});

2. spawn

spawn is similar to exec, but it returns a child process object and allows access to stdout and stderr streams, suitable for long-running processes.

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const { spawn } = require("child_process");
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const ls = spawn("ls", ["-l"]);
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ls.stdout.on("data", (data) => {
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  console.log(`Stdout: ${data}`);
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});
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ls.stderr.on("data", (data) => {
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  console.error(`Stderr: ${data}`);
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});
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ls.on("close", (code) => {
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  console.log(`Child process exited with code ${code}`);
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});

3. fork

fork is used to create a Node.js child process, ideal for inter-process communication. fork is a special case of spawn, designed specifically for creating Node.js child processes with built-in communication channels.

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const { fork } = require("child_process");
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const child = fork("child.js");
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child.on("message", (message) => {
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  console.log(`Received message from child: ${message}`);
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});
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child.send("Hello from parent");

Inter-Process Communication (IPC)

In Node.js, inter-process communication can be achieved using the message event, particularly with child processes created using fork. Parent and child processes can send and receive messages to and from each other.

• Parent Process Sends a Message to Child Process:

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  const { fork } = require("child_process");
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  const child = fork("child.js");
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  child.send({ hello: "world" });

• Child Process Receives and Sends Messages:

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  process.on("message", (message) => {
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    console.log(`Received message from parent: ${message.hello}`);
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    process.send({ reply: "Hello from child" });
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  });

This message-passing mechanism makes inter-process communication simple and efficient, and since processes do not share memory, it ensures each process’s independence and stability.

By understanding the concepts of processes and threads, and how to use them in Node.js, developers can write more efficient and stable applications. Processes and threads play a crucial role in concurrent programming, and the tools provided by Node.js make these operations more accessible.