Context in Go

In this lesson, explore context in go through one small Go program, and connect its output to the language rules behind it.

context.Context carries cancellation signals, deadlines and request-scoped values through call chains. Pass it as the first parameter to operations that can block or must stop with their caller.

A Context is not a generic settings bag. Use WithValue for request-scoped metadata when truly needed, not ordinary function inputs.

Follow this diagram before executing the example. Check where a value or decision changes what runs next.

This example is a complete program. Save it as main.go or paste it into the Go Playground.

Go code

package main

import (
	"context"
	"fmt"
)

func label(ctx context.Context) string {
	if err := ctx.Err(); err != nil {
		return "stopped"
	}
	return "running"
}
func main() {
	ctx := context.Background()
	fmt.Println("Task:", label(ctx))
}

Output

Task: running

Background returns a base context with no cancellation. Err is nil, so the helper returns running.

• Do not store a context in a long-lived struct without a specific design reason.
• Do not pass nil for Context; use context.Background or context.TODO.

Add a context parameter to a function that validates whether work should continue.

Tip: Edit the example above, predict the output, and run the modified code to test your reasoning.

You have practiced Context in Go in a small, self-contained program. The important habit is to predict what runs, inspect the actual output and distinguish the language rule from the particular example.

Before continuing, make sure you can explain the program to someone who has not seen it, including the line that changes its result.