What is a mutex in C++ and how do I use it?

What is a mutex in C++ and how do I use it?

A mutex, or mutual exclusion, is a synchronization primitive used to prevent multiple threads from accessing shared resources simultaneously. In C++, you can use the std::mutex class from the <mutex> header to implement it.

Can you show me a simple example of using std::mutex?

Sure! Here's a basic example:

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

std::mutex mtx;

void printThreadId(int id) {
    mtx.lock();  // Lock the mutex
    std::cout << "Thread ID: " << id << '\n';
    mtx.unlock();  // Unlock the mutex
}

int main() {
    std::thread threads[5];
    for (int i = 0; i < 5; ++i) {
        threads[i] = std::thread(printThreadId, i);
    }
    for (auto& th : threads) {
        th.join();
    }
    return 0;
}

What happens if I forget to unlock the mutex?

If you forget to unlock the mutex, it can lead to a deadlock situation where other threads are unable to acquire the lock and get stuck waiting indefinitely. It's crucial to always unlock the mutex after locking it.

Are there any alternatives to std::mutex?

Yes, there are alternatives like std::recursive_mutex, which allows the same thread to lock it multiple times, and std::shared_mutex, which allows multiple readers or one writer.