Concurrent execution model in Go

Introduction

Concurrent execution lets your program do many things at the same time. This helps it run faster and handle multiple tasks smoothly.

When you want to download files while still letting the user interact with the app.

When you need to handle many users connecting to a server at once.

When you want to run background tasks without stopping the main program.

When processing large data in parts to save time.

When you want to improve performance by using multiple CPU cores.

Syntax

Go

go func() {
    // code to run concurrently
}()

This syntax starts a new goroutine, which is a lightweight thread.

The code inside the function runs at the same time as the rest of the program.

Examples

This starts a new goroutine that prints a message concurrently.

Go

go func() {
    println("Hello from goroutine")
}()

This runs the sayHello function concurrently while main continues.

Go

func sayHello() {
    println("Hello")
}

func main() {
    go sayHello()
    println("Main function")
}

This starts three goroutines, each printing its number.

Go

for i := 1; i <= 3; i++ {
    go func(n int) {
        println("Goroutine", n)
    }(i)
}

Sample Program

This program runs printNumbers in a goroutine while main prints messages. The sleep in main lets the goroutine finish printing.

Go

package main

import (
    "fmt"
    "time"
)

func printNumbers() {
    for i := 1; i <= 5; i++ {
        fmt.Println("Number", i)
        time.Sleep(100 * time.Millisecond)
    }
}

func main() {
    go printNumbers() // run concurrently
    fmt.Println("Main function continues")
    time.Sleep(600 * time.Millisecond) // wait to see goroutine output
    fmt.Println("Main function ends")
}

Important Notes

Goroutines are very lightweight compared to traditional threads.

Use time.Sleep or synchronization to let goroutines finish before main ends.

Channels are often used to communicate between goroutines (not shown here).

Summary

Concurrent execution lets your program do multiple things at once.

In Go, goroutines are used to run code concurrently with simple syntax.

Remember to manage timing so goroutines have time to run before the program exits.

Practice

1. What is a goroutine in Go's concurrent execution model?

easy

A. A lightweight thread managed by the Go runtime

B. A type of variable used for synchronization

C. A special function that runs only once

D. A package for handling errors

Solution

1. Step 1: Understand goroutine concept

   A goroutine is a function or method that runs concurrently with other goroutines.

2. Step 2: Identify goroutine characteristics

   It is lightweight and managed by Go's runtime, unlike OS threads which are heavier.

3. Final Answer:

   A lightweight thread managed by the Go runtime -> Option A

4. Quick Check:

   Goroutine = lightweight thread [OK]

Hint: Goroutine = lightweight thread in Go [OK]

Common Mistakes:

• Confusing goroutine with OS thread
• Thinking goroutine is a variable type
• Assuming goroutine runs only once

2. Which of the following is the correct syntax to start a goroutine that calls function doWork()?

easy

A. go doWork()

B. goroutine doWork()

C. start doWork()

D. run doWork()

Solution

1. Step 1: Recall goroutine syntax

   In Go, to start a goroutine, prefix the function call with the keyword go.

2. Step 2: Match syntax with options

   Only go doWork() uses the correct keyword and syntax.

3. Final Answer:

   go doWork() -> Option A

4. Quick Check:

   Start goroutine with 'go' keyword [OK]

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

Common Mistakes:

• Using 'goroutine' keyword instead of 'go'
• Using 'start' or 'run' which are invalid
• Omitting the 'go' keyword

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

package main
import (
  "fmt"
  "time"
)
func main() {
  go fmt.Println("Hello from goroutine")
  fmt.Println("Hello from main")
  time.Sleep(100 * time.Millisecond)
}

medium

A. No output

B. Hello from goroutine\nHello from main

C. Hello from main

D. Hello from main\nHello from goroutine

Solution

1. Step 1: Understand goroutine and main execution

   The goroutine prints "Hello from goroutine" concurrently, while main prints "Hello from main" immediately.

2. Step 2: Analyze timing with Sleep

   The time.Sleep allows the goroutine time to run before the program exits, so both lines print.

3. Final Answer:

   Hello from main\nHello from goroutine -> Option D

4. Quick Check:

   Sleep allows goroutine output after main [OK]

Hint: Sleep lets goroutine finish before program ends [OK]

Common Mistakes:

• Ignoring need for sleep to let goroutine run
• Assuming goroutine output always prints first
• Expecting no output due to race condition

4. Identify the error in this Go code snippet that tries to run a goroutine:

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

medium

A. Missing import of time package

B. Program exits before goroutine runs

C. Syntax error in anonymous function

D. Cannot use go with anonymous functions

Solution

1. Step 1: Check syntax correctness

   The anonymous function syntax and goroutine start are correct; no syntax errors.

2. Step 2: Analyze program flow

   The main function exits immediately after starting the goroutine, so "Running" may never print.

3. Final Answer:

   Program exits before goroutine runs -> Option B

4. Quick Check:

   Program ends before goroutine runs [OK]

Hint: Add sleep or sync to wait for goroutine [OK]

Common Mistakes:

• Thinking syntax is wrong for anonymous goroutine
• Forgetting program ends immediately
• Assuming goroutine blocks main automatically

5. You want to run 3 goroutines that each print their number (1, 2, 3). Which code correctly prints all numbers reliably before the program exits?

package main
import (
  "fmt"
  "sync"
)
func main() {
  var wg sync.WaitGroup
  for i := 1; i <= 3; i++ {
    wg.Add(1)
    go func(n int) {
      defer wg.Done()
      fmt.Println(n)
    }(i)
  }
  // What should be here?
}

hard

A. wg.Done()

B. time.Sleep(1 * time.Second)

C. wg.Wait()

D. close(wg)

Solution

1. Step 1: Understand WaitGroup usage

   WaitGroup tracks goroutines; wg.Add(1) before start, wg.Done() after done.

2. Step 2: Ensure main waits for all goroutines

   Calling wg.Wait() blocks main until all goroutines call Done().

3. Final Answer:

   wg.Wait() -> Option C

4. Quick Check:

   WaitGroup.Wait() waits for goroutines [OK]

Hint: Use wg.Wait() to wait all goroutines finish [OK]

Common Mistakes:

• Using Sleep instead of WaitGroup for sync
• Trying to close WaitGroup (not allowed)
• Calling Done() in main instead of goroutine