Introduction to C++ Multithreading

1. Introduction

This tutorial aims to introduce you to the concept of multithreading in C++. You'll learn what threads are, how they work, and why they are used in programming. By the end of this tutorial, you should be able to write, understand, and analyze multithreaded programs in C++.

You will learn

• The fundamental concepts of threads and multithreading
• How to create and manage threads in C++
• How to synchronize threads

Prerequisites

• Basic understanding of C++ programming
• Familiarity with concepts like functions, classes, and objects

2. Step-by-Step Guide

Threads in C++

Threads are the smallest sequences of programmed instructions that can be managed independently by a scheduler. Multithreading is the ability of a processor to execute multiple threads concurrently. In C++, you can use the <thread> library to create and manage threads.

Creating a Thread

In C++, you can create a thread by creating an object of the std::thread class and passing a function to the constructor.

#include <iostream>
#include <thread>

void printHello() {
  std::cout << "Hello, World!" << std::endl;
}

int main() {
  std::thread threadObj(printHello);
  threadObj.join();
  return 0;
}

The threadObj.join() line ensures that the main thread waits for threadObj to finish execution before it continues.

3. Code Examples

Example 1: Basic Multithreading

#include <iostream>
#include <thread>

// Function to be executed by thread
void function_1() {
    std::cout << "Function 1 has been called!" << std::endl;
}

int main() {
    // Creating a thread that executes function_1
    std::thread t1(function_1);

    // Wait for t1 to finish
    t1.join();

    std::cout << "Main function has finished execution" << std::endl;

    return 0;
}

Output

Function 1 has been called!
Main function has finished execution

Example 2: Multithreading with Parameters

#include <iostream>
#include <thread>

// Function to calculate the sum of two numbers
void function_2(int num1, int num2) {
    std::cout << "The sum is: " << num1 + num2 << std::endl;
}

int main() {
    std::thread t2(function_2, 10, 20);

    t2.join();

    return 0;
}

Output

The sum is: 30

4. Summary

• Threads are the smallest sequences of programmed instructions that can be managed independently.
• Multithreading allows for concurrent execution of two or more parts of a program to maximize utilization of CPU.
• In C++, you can create threads using the std::thread class in the <thread> library.
• The join() function allows the main thread to wait for the other threads to finish their execution.

Next, you could learn about more advanced topics like thread synchronization, thread pools, and thread safety. Some additional resources include the <thread> library documentation and C++ Concurrency in Action by Anthony Williams.

5. Practice Exercises

Exercise 1: Write a program that creates a separate thread to print numbers from 1 to 10.

Exercise 2: Write a program that creates two threads. One thread prints all even numbers from 1 to 20, and the other thread prints all odd numbers.

Exercise 3: Write a program where multiple threads calculate the factorial of a number, and the main thread prints the result.

Exercise Solutions

1. Solution for Exercise 1

#include <iostream>
#include <thread>

void printNumbers() {
  for(int i = 1; i <= 10; i++) {
    std::cout << i << std::endl;
  }
}

int main() {
  std::thread t(printNumbers);
  t.join();
  return 0;
}

1. Solution for Exercise 2 and 3 can be found in this link

Remember, practice is key to mastering multithreading. Try to come up with and solve more complex problems to improve your understanding. Happy coding!