Why concurrency is needed in Go - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start a new goroutine.

Go

go [1]()

Drag options to blanks, or click blank then click option'

Afmt.Println

Bmain

CsayHello

Dtime.Sleep

Attempts:

3 left

💡 Hint

Common Mistakes

Using fmt.Println directly after go without calling a function.

Trying to start the main function as a goroutine.

Using time.Sleep without parentheses.

The go keyword starts a new goroutine running the function sayHello.

2fill in blank

medium

Complete the code to wait for a goroutine to finish using a channel.

Go

done := make(chan bool)
go func() {
    fmt.Println("Working...")
    done [1] true
}()
<-done

Drag options to blanks, or click blank then click option'

A<-

B<-chan

D<-chan bool

Attempts:

3 left

💡 Hint

Common Mistakes

Using the receive operator <- on the left side incorrectly.

Confusing channel type declarations with send/receive operations.

To send a value to a channel, use done <- true.

3fill in blank

hard

Fix the error in the code to correctly launch multiple goroutines.

Go

for i := 0; i < 3; i++ {
    go func() {
        [1]
        fmt.Println(i)
    }()
}

Drag options to blanks, or click blank then click option'

Avar i

Bi

Ci int

Di := i

Attempts:

3 left

💡 Hint

Common Mistakes

Not capturing the loop variable causes all goroutines to print the same value.

Trying to declare i with a type inside the loop incorrectly.

Passing i as a parameter inside the goroutine fixes the closure capturing issue.

4fill in blank

hard

Fill both blanks to create a buffered channel and send a value.

Go

ch := make(chan int, [1])
ch [2] 5

Drag options to blanks, or click blank then click option'

A1

B<-

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using zero as buffer size creates an unbuffered channel.

Using the receive operator instead of send operator.

A buffered channel of size 1 is created, then the value 5 is sent using ch <- 5.

5fill in blank

hard

Fill all three blanks to create a map with word lengths using concurrency.

Go

words := []string{"go", "code", "fun"}
lengths := make(map[string]int)
var mu sync.Mutex
for _, word := range words {
    go func(w string) {
        mu.Lock()
        lengths[[1]] = len([2])
        mu.Unlock()
    }([3])
}

Drag options to blanks, or click blank then click option'

Aw

Cword

Attempts:

3 left

💡 Hint

Common Mistakes

Using the loop variable word directly inside the goroutine causes race conditions.

Not locking the map before writing causes concurrent map writes error.

The goroutine uses the parameter w to safely update the map with the length of each word.

Practice

1. Why do we need concurrency in Go programs?

easy

A. To simplify the code by removing all loops and conditions.

B. To allow multiple tasks to run at the same time, improving speed and responsiveness.

C. To make the program use less memory by running tasks one after another.

D. To avoid using functions and write everything in the main block.

Solution

1. Step 1: Understand concurrency purpose

   Concurrency allows a program to handle multiple tasks at once instead of waiting for one to finish before starting another.

2. Step 2: Relate concurrency to Go

   Go uses goroutines to run tasks concurrently, which helps programs be faster and more responsive.

3. Final Answer:

   To allow multiple tasks to run at the same time, improving speed and responsiveness. -> Option B

4. Quick Check:

   Concurrency = multiple tasks at once [OK]

Hint: Concurrency means doing many things at once [OK]

Common Mistakes:

• Thinking concurrency reduces memory by running tasks sequentially
• Confusing concurrency with simpler code structure
• Believing concurrency removes the need for functions

2. Which of the following is the correct way to start a goroutine in Go?

easy

A. go myFunction()

B. start myFunction()

C. run myFunction()

D. goroutine myFunction()

Solution

1. Step 1: Recall Go syntax for goroutines

   In Go, the keyword go is used before a function call to start it as a goroutine.

2. Step 2: Check each option

   Only go myFunction() uses the correct go keyword syntax; others are invalid in Go.

3. Final Answer:

   go myFunction() -> Option A

4. Quick Check:

   Start goroutine with 'go' keyword [OK]

Hint: Use 'go' before function to start goroutine [OK]

Common Mistakes:

• Using 'start' or 'run' instead of 'go'
• Forgetting the 'go' keyword before function call
• Trying to declare goroutine with 'goroutine' keyword

3. What will be the output of this Go program?

package main
import (
  "fmt"
  "time"
)
func sayHello() {
  fmt.Println("Hello")
}
func main() {
  go sayHello()
  time.Sleep(1 * time.Second)
  fmt.Println("World")
}

medium

A. World\nHello

B. Hello

C. Hello\nWorld

D. World

Solution

1. Step 1: Understand goroutine and sleep

   The function sayHello runs as a goroutine, so it runs concurrently with main. The main function sleeps 1 second to allow sayHello to print.

2. Step 2: Determine print order

   Because of the sleep, "Hello" prints first from the goroutine, then "World" prints after sleep ends.

3. Final Answer:

   Hello World -> Option C

4. Quick Check:

   Goroutine prints 'Hello' before main prints 'World' [OK]

Hint: Sleep lets goroutine finish before main prints [OK]

Common Mistakes:

• Ignoring time.Sleep and missing 'Hello' output
• Assuming 'World' prints before 'Hello'
• Thinking goroutine blocks main function

4. Identify the problem in this Go code snippet:

package main
import "fmt"
func main() {
  go func() {
    fmt.Println("Running")
  }()
  fmt.Println("Done")
}

medium

A. Goroutines cannot be used inside main function.

B. The anonymous function syntax is incorrect.

C. The fmt package is not imported properly.

D. The program may exit before the goroutine runs, so "Running" might not print.

Solution

1. Step 1: Analyze goroutine execution timing

   The goroutine runs concurrently, but main may finish and exit before the goroutine prints "Running".

2. Step 2: Check code correctness

   The anonymous function syntax and imports are correct; goroutines can run inside main.

3. Final Answer:

   The program may exit before the goroutine runs, so "Running" might not print. -> Option D

4. Quick Check:

   Program exit can stop goroutine early [OK]

Hint: Main may exit before goroutine finishes [OK]

Common Mistakes:

• Thinking anonymous function syntax is wrong
• Believing goroutines can't run in main
• Ignoring program exit timing

5. You want to download 3 files concurrently in Go and print "All done" only after all downloads finish. Which approach correctly uses concurrency to achieve this?

hard

A. Start 3 goroutines for downloads and use a sync.WaitGroup to wait for all to finish before printing "All done".

B. Call the download functions one after another without goroutines, then print "All done".

C. Start 3 goroutines but print "All done" immediately after starting them without waiting.

D. Use a for loop to start downloads but do not synchronize; rely on time.Sleep to wait.

Solution

1. Step 1: Understand concurrency with synchronization

   Starting goroutines runs downloads concurrently, but we must wait for all to finish before printing "All done".

2. Step 2: Use sync.WaitGroup for waiting

   sync.WaitGroup lets main wait until all goroutines complete, ensuring correct order.

3. Final Answer:

   Start 3 goroutines for downloads and use a sync.WaitGroup to wait for all to finish before printing "All done". -> Option A

4. Quick Check:

   WaitGroup synchronizes goroutines before final print [OK]

Hint: Use WaitGroup to wait for all goroutines [OK]

Common Mistakes:

• Not waiting for goroutines before printing
• Using sleep instead of proper synchronization
• Running downloads sequentially without concurrency