Multithreading in C++

In this tutorial, I will walk you through one of the more important concepts in the world of programming and C++, especially if you plan to work on software development or similar domains. I’m talking about C++ multithreading, and from my experience, I’ve seen many students struggling to understand the concepts of C++ multithreading.

If you’ve also been confused by what is multithreading in cpp, and have looked for multithreading in C++ example, you’re just in the right place. By the end of this tutorial, you will have a good grasp on C++ multithreading, and to add to that, you’ll also know about some C++ multithreading interview questions, C++ multithreading book, and a lot more.

So, let’s dive in and get started with our C++ multithreading tutorial.

What is Multithreading in C++?

In today's world of computing, where speed and effectiveness are crucial, using C++ multithreading is a strong tool. No matter if you are creating a platform for high-frequency trading, an application with quick graphical user interface (GUI) response or even a complex simulation - utilizing C++ multithreading can greatly improve your program's performance. But what does this mean?

In C++, multithreading lets a computer program do many tasks at once. We can understand this like how numerous people working in parallel can complete different parts of one job simultaneously. This feature is crucial now, with the rise of multi-core processors that allow for more efficient use of available hardware resources to increase speed and effectiveness in executing our applications.

Why Use Multithreading in C++?

You may ask, why do we care about multithreading? Well, these are some good reasons:

• Better performance: By executing tasks at the same time, your programs can run quicker and with less delay. Think about having a big computation task such as processing huge amounts of data or running complicated simulations. When you use C++ multithreading, this task can be divided into many threads where each thread manages a part of the data at once. This helps in decreasing the total time taken to process everything together.

• Resource utilization: Multithreading can better utilize the CPU resources, particularly in multi-core processors. Contemporary CPUs possess multiple cores; therefore, if a program lacks multithreading, it may only use one core while leaving others idle. C++ multi-threaded programming allows your applications to make the most of hardware by distributing work across all available cores.

• Responsiveness: GUI applications, for example, can use multithreading to ensure that the user interface stays responsive while it carries out tasks in the background. Did you ever notice a situation where an application goes into a freeze mode or stops reacting when performing some task? C++ multithreading helps to avoid this by shifting tasks that take up lots of time onto different threads; this leaves the main thread free for handling interactions with users in a more efficient manner.

Getting Started with C++ Multithreading

Before we jump into C++ multithreading examples, let’s set up the basics. The standard library in C++11 and later versions provides the necessary tools to implement multithreading.

Creating Threads

Creating threads in C++ is straightforward. Here’s a simple example to illustrate:

Example:

#include <iostream>
#include <thread>
void printMessage() {
std::cout << "Hello from thread!" << std::endl;
}
int main() {
std::thread t(printMessage);
t.join(); // Wait for the thread to finish
return 0;
}

Output:

Hello from thread!

In this example, we create a thread that runs the printMessage function. The join() method ensures the main thread waits for the new thread to complete before exiting.

Practical Multithreading in C++ Examples

Now that we’ve covered the basics, let’s explore more practical multithreading in C++ examples.

Example 1: Parallel Processing

Imagine you have a large array of numbers, and you want to find their sum. Using multithreading, you can split the task and process different parts of the array simultaneously.

Example:

#include <iostream>
#include <thread>
#include <vector>
void partialSum(const std::vector<int>& arr, int start, int end, int& result) {
result = 0;
for (int i = start; i < end; ++i) {
result += arr[i];
}
}
int main() {
std::vector<int> numbers(100, 1); // Array of 100 numbers all set to 1
int result1 = 0, result2 = 0;
std::thread t1(partialSum, std::ref(numbers), 0, 50, std::ref(result1));
std::thread t2(partialSum, std::ref(numbers), 50, 100, std::ref(result2));
t1.join();
t2.join();
int total = result1 + result2;
std::cout << "Total sum: " << total << std::endl;
return 0;
}

Output:

Total sum:100

Example 2: Using C++ Multithreading Library

C++ provides a rich set of libraries for multithreading. One of the most commonly used is the <thread> library, which we’ve already seen in action. Another powerful library is <future> which can be used for asynchronous tasks.

Example:

#include <iostream>
#include <future>
int factorial(int n) {
int result = 1;
for (int i = 1; i <= n; ++i) {
result *= i;
}
return result;
}
int main() {
std::future<int> fut = std::async(factorial, 5);
std::cout << "Factorial of 5 is " << fut.get() << std::endl;
return 0;
}

Output:

Factorial of 5 is 120

C++ Multithreading Projects and Interview Questions

You encounter more complicated situations as you go further into multi-threaded programming in C++. Let's talk about some advanced topics in the world of C++ multithreading quickly to help you make your understanding stronger and be ready for real-world use or interviews.

C++ Multithreading Projects

If you are looking for more hands-on experience in C++ multithreading, working on projects is a good way to reinforce your knowledge. Practical projects assist in putting into action what has been learned and also help with preparation for real-life scenarios.

Below are some C++ multithreading project suggestions that utilize your knowledge and understanding of multi threaded programming in C++.

1. Multithreaded Web Server: Construct an uncomplicated web server that can handle several client requests at once. Employ C++ multithreading to process each client request in a distinct thread, enhancing the server's answer time and productivity.

2. System for Parallel File Processing: Develop a system that can process big files simultaneously. You may create a. program which reads, handles and writes distinct sections of a file at the same time concurrently.. This method has potential to reduce processing duration, especially with huge sets of data.

You will get practical experience in C++ multithreading from these projects, which will make you skilled in managing threads, synchronizing them and improving performance.

C++ Multithreading Interview Questions

Getting ready for an interview? These are the usual C++ multithreading interview questions you can begin with:

1. What are the benefits of multithreading in C++?

Multithreading boosts performance, increases CPU resource usage efficiency and maintains application reactivity by permitting many threads to run at the same time.

2. How do you create and manage threads in C++?

In C++, you can make threads with the help of <thread> library. The actions for managing threads are join(), detach() and thread synchronization using mutexes along with condition variables.

3. Explain the concept of thread synchronization.

Synchronization of threads is very important because it avoids data races and guarantees that actions performed by different threads are safe. Thread synchronization is done using synchronization tools such as mutexes (mutual exclusion objects), locks, and condition variables to control access to shared resources.

4. What is a race condition, and how do you avoid it?

Race condition is a situation that happens when two or more threads are trying to access shared data at the same moment, causing uncertain results. This can be stopped by using synchronization techniques such as mutexes. These guarantee only one thread can go into the shared resource at any given time.

Remember, these are just a few of the questions that can be asked as a part of C++ multithreading interview questions. The idea is to prepare yourself well by attending classes and reading C++ multithreading book so that all the C++ multithreading interview questions can be handled with ease!

Recommended C++ Multithreading Book

For those who prefer a deep dive into the subject, I highly recommend the book "C++ Concurrency in Action" by Anthony Williams. It’s an excellent resource for understanding the nuances of multithreading in C++. This book covers everything from the basics of thread management to advanced concurrency techniques, making it a must-read for anyone serious about mastering C++ multithreading.

If you’re looking to dive deeper and get more hands on, I recommend you check out upGrad’s courses in the world of software engineering and computer science!

Concluding Remarks

As we wrap up this comprehensive tutorial on C++ multithreading, I hope you've gained a solid understanding of the key concepts and practical applications of multithreading in C++. We've covered the basics of creating and managing threads, explored practical examples to illustrate how multithreading can enhance performance and responsiveness, and even touched on advanced topics such as multithreaded projects and common interview questions.

C++ multithreading is a powerful tool that can significantly improve the efficiency and performance of your applications. By leveraging the capabilities of multi-threaded programming in C++, you can fully utilize modern multi-core processors, ensuring that your applications run faster and more efficiently. Whether you're working on a multithreaded web server, a parallel file processing system, or any other complex project, the principles and techniques you've learned here will be invaluable.

If you're keen on delving deeper into C++ multithreading, consider taking on challenging projects or preparing for interviews with the commonly asked C++ multithreading interview questions. Additionally, investing in a good C++ multithreading book like "C++ Concurrency in Action" by Anthony Williams can provide you with a deeper understanding and advanced techniques.

For those of you looking to expand your expertise beyond C++ multithreading, I highly recommend checking out upGrad’s comprehensive courses in software engineering and computer science. These courses offer in-depth knowledge and hands-on experience, covering a wide range of topics that are essential for modern software development.

Frequently Asked Questions (FAQs)

What is multithreading in C++?

Multithreading in C++ allows a program to execute multiple threads concurrently, enhancing performance and responsiveness.

Why use multithreading in C++?

Multithreading improves performance, optimizes resource utilization, and keeps applications responsive.

What are the different types of multithreading in C++?

There are several types, including parallel processing, asynchronous programming, and concurrent data structures.

Is C++ good for multithreading?

Yes, C++ is well-suited for multithreading due to its powerful standard library and support for low-level thread management.

Can I use multithreading in C++ with classes and objects?

Absolutely! C++ supports multithreading with classes and objects, allowing for more structured and modular code.

Are there any libraries or frameworks for multithreading in C++?

Yes, libraries like <thread>, <future>, and Boost.Thread are commonly used for multithreading in C++.

Does C++ multithreading use multiple cores?

Yes, C++ multithreading can utilize multiple cores, significantly improving performance on multi-core processors.

Is there multiprocessing in C++?

While C++ primarily focuses on multithreading, it also supports multiprocessing through libraries like Boost.Process.