IPC communication between processes in Node.js - Step-by-Step Execution

Concept Flow - IPC communication between processes

Parent process starts

↓

Fork child process

↓

Parent sends message

↓

Child processes message

↓

Child sends reply

↓

Processes communicate back and forth

↓

Processes end communication

Shows how a parent process forks a child, then both send and receive messages to communicate.

Execution Sample

Node.js

const { fork } = require('child_process');
const child = fork('child.js');
child.on('message', msg => console.log('Parent got:', msg));
child.send('Hello Child');

Parent process forks a child and sends a message; listens for child's reply.

Execution Table

Step	Process	Action	Message Sent	Message Received	Result
1	Parent	Fork child process			Child process created
2	Parent	Send message to child	Hello Child		Message sent to child
3	Child	Receive message from parent		Hello Child	Child got message
4	Child	Send reply to parent	Hello Parent		Reply sent to parent
5	Parent	Receive reply from child		Hello Parent	Parent got reply
6	Parent & Child	Continue communication or end			Processes communicate or close
7	Parent & Child	End communication			Processes exit or disconnect

💡 Communication ends when processes close or disconnect.

Variable Tracker

Variable	Start	After Step 2	After Step 4	Final
child	undefined	Child process object	Child process object	Child process object
messageToChild	undefined	"Hello Child"	"Hello Child"	"Hello Child"
messageToParent	undefined	undefined	"Hello Parent"	"Hello Parent"

Key Moments - 3 Insights

Why does the parent need to listen for messages from the child?

Because IPC is two-way; the child can send replies or data back, so the parent must listen to receive them (see execution_table step 5).

What happens if the child sends a message before the parent starts listening?

The message might be missed or cause errors; both sides must set up listeners before sending messages to ensure communication works (refer to execution_table steps 2 and 3).

Can the parent and child send messages at any time?

Yes, as long as both have listeners set up, they can send messages asynchronously back and forth (see execution_table step 6).

Visual Quiz - 3 Questions

Look at the execution table, what message does the parent send at step 2?

A "Hello Child"

B "Hello Parent"

C "Start"

D "Goodbye"

💡 Hint

Check the 'Message Sent' column at step 2 in the execution_table.

At which step does the child send a reply to the parent?

A Step 3

B Step 4

C Step 5

D Step 6

💡 Hint

Look for 'Send reply to parent' in the 'Action' column of execution_table.

If the parent never listens for messages, what happens at step 5?

A Parent receives the message normally

B Child never sends a reply

C Parent misses the child's reply

D Child process crashes

💡 Hint

Refer to key_moments about listening before sending and execution_table step 5.

Concept Snapshot

IPC communication in Node.js:
- Parent forks child with fork()
- Both use .send() to send messages
- Both listen with 'message' event
- Messages pass as objects or strings
- Communication is asynchronous and two-way
- Both must set listeners before sending

Full Transcript

In Node.js, IPC communication happens when a parent process creates a child process using fork(). The parent can send messages to the child using child.send(), and the child listens for these messages with the 'message' event. Similarly, the child can send messages back to the parent, which listens for them. This two-way communication allows processes to exchange data asynchronously. Both sides must set up listeners before sending messages to avoid missing data. Communication continues until processes disconnect or exit.