Introduction to Concurrency

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

Concurrency means organizing multiple tasks so their progress can overlap. In Go, goroutines run functions independently, while channels and synchronization tools coordinate them.

The example runs two calculations concurrently but gives their results a fixed order when printing. Starting goroutines alone does not guarantee they finish before main exits.

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 "fmt"

func main() {
	results := make(chan int, 2)
	go func() { results <- 2 * 3 }()
	go func() { results <- 4 * 5 }()
	a, b := <-results, <-results
	fmt.Println("Sum:", a+b)
}

Output

Sum: 26

Both goroutines send exactly one computed integer. The two receives wait for both results, and addition is order-independent, so Sum: 26 is stable.

• A goroutine runs independently; launching one is not the same as waiting for it.
• The order in which two goroutines finish is not guaranteed.

Add a third multiplication goroutine and receive a third result before printing the sum.

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

You have practiced Introduction to Concurrency 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.