Why concurrency is needed in Go - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of concurrent goroutines

What is the output of this Go program that launches two goroutines printing numbers?

Go

package main
import (
	"fmt"
	"time"
)
func main() {
	go func() {
		for i := 1; i <= 3; i++ {
			fmt.Print(i)
			time.Sleep(10 * time.Millisecond)
		}
	}()
	go func() {
		for i := 4; i <= 6; i++ {
			fmt.Print(i)
			time.Sleep(10 * time.Millisecond)
		}
	}()
	time.Sleep(50 * time.Millisecond)
}

A 123456

B Any interleaved combination of digits 1 to 6

C 456123

D Program does not print anything

💡 Hint

Think about how goroutines run independently and may print in any order.

Goroutines run concurrently, so their print statements can interleave in any order. The program prints digits 1 to 6 but the order is not guaranteed.

🧠 Conceptual

intermediate

Why use concurrency in Go?

Which of the following best explains why concurrency is needed in Go programs?

A To prevent any code from running in parallel

B To make programs run slower and use more memory

C To avoid using functions and loops

D To allow multiple tasks to run at the same time improving efficiency and responsiveness

💡 Hint

Think about how computers can do many things at once.

Concurrency lets Go programs run multiple tasks simultaneously, making better use of CPU and improving program responsiveness.

🔧 Debug

advanced

Identify the concurrency issue

What error or problem will this Go code cause when run?

Go

package main
import (
	"fmt"
)
func main() {
	for i := 0; i < 3; i++ {
		go func(i int) {
			fmt.Println(i)
		}(i)
	}
	// Wait for goroutines
	var input string
	fmt.Scanln(&input)
}

A Prints 0, 1, 2 as expected

B Compilation error due to missing import

C Prints 3, 3, 3 because of variable capture in goroutine

D Deadlock error at runtime

💡 Hint

Think about how the loop variable is used inside the goroutine.

By passing the loop variable i as a parameter to the goroutine function, each goroutine gets its own copy, so it prints 0, 1, 2 as expected.

📝 Syntax

advanced

Identify the syntax error in concurrency code

Which option contains a syntax error in Go concurrency code?

A go func() { fmt.Println("Hello") }

B )(} )"olleH"(nltnirP.tmf { )(cnuf og

C go func() { fmt.Println("Hello") }()

D o func() { fmt.Println("Hello") }()

💡 Hint

Check if the anonymous function is called immediately.

Option A misses the () after the anonymous function, so the function is not called and causes a syntax error.

🚀 Application

expert

How many goroutines run concurrently?

Given this Go program, how many goroutines run concurrently at peak?

Go

package main
import (
	"fmt"
	"time"
)
func worker(id int) {
	fmt.Printf("Worker %d starting\n", id)
	time.Sleep(50 * time.Millisecond)
	fmt.Printf("Worker %d done\n", id)
}
func main() {
	for i := 1; i <= 5; i++ {
		go worker(i)
	}
	time.Sleep(100 * time.Millisecond)
}

A No goroutines run concurrently

B 1 goroutine at a time

C 5 goroutines run concurrently

D 10 goroutines run concurrently

💡 Hint

Count how many goroutines are started and how long they run.

The program starts 5 goroutines almost at the same time, so all 5 run concurrently during the sleep period.