Concurrency is an essential aspect of modern software development, as it allows programs to perform multiple tasks simultaneously. However, concurrent access to shared resources can lead to race conditions and data inconsistency. To protect such resources, we can use mutexes.

In this blog post, we will explore how to use mutexes with the std::jthread class from the C++20 standard library to ensure thread-safe access to shared data.

What is std::jthread?

Introduced in C++20, std::jthread is a class that represents a joinable thread. It provides a convenient way to manage threads and automatically joins them upon destruction. This means we don’t need to explicitly call join() or detach().

Using Mutexes with std::jthread

To use a mutex with std::jthread, we need to include the <mutex> header file, declare a mutex object, and use its lock and unlock mechanism to protect the shared resource.

Here’s an example:

#include <iostream>
#include <mutex>
#include <thread>

std::mutex mtx; // Declare a mutex object

void incrementCounter(int& counter) {
    std::lock_guard<std::mutex> lock(mtx); // Lock the mutex
    counter++; // Manipulate the shared resource
    // lock is automatically released when the function scope ends
}

int main() {
    int counter = 0;

    std::jthread thread1(incrementCounter, std::ref(counter));
    std::jthread thread2(incrementCounter, std::ref(counter));

    // Wait for the threads to complete their tasks
    thread1.join();
    thread2.join();

    std::cout << "Counter value: " << counter << std::endl;

    return 0;
}

In the above code, we create a std::mutex object called mtx to guard the access to the shared counter variable. By using the std::lock_guard class together with the mutex, we ensure that only one thread can access the shared resource at a time. The lock is automatically released when the std::lock_guard object goes out of scope.

We then create two std::jthread objects, thread1 and thread2, and pass the incrementCounter function along with the counter variable by reference. Each thread increments the counter using the mutex-protected function.

Finally, we join the threads and print the final value of the counter variable.

Conclusion

Using mutexes with std::jthread allows us to synchronize access to shared resources and ensure thread safety. By protecting critical sections of code with mutexes, we prevent race conditions and data corruption.

Ensure that you use mutexes judiciously and only lock them when necessary to minimize contention and maximize parallelism in your concurrent programs.

#cpp #concurrency