What are mutexes in C++ and how do I use them?

What are mutexes in C++ and how do I use them?

Mutexes, or mutual exclusions, are synchronization primitives used to protect shared data from being simultaneously accessed by multiple threads. In C++, you can use the std::mutex class from the standard library to create a mutex.

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

Sure! Here's a basic example:

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

std::mutex mtx;

void printNumbers(int id) {
    mtx.lock();  // Lock the mutex
    for (int i = 0; i < 5; ++i) {
        std::cout << "Thread " << id << ": " << i << '\n';
    }
    mtx.unlock();  // Unlock the mutex
}

int main() {
    std::thread t1(printNumbers, 1);
    std::thread t2(printNumbers, 2);
    t1.join();
    t2.join();
    return 0;
}

This code creates two threads that print numbers while ensuring that the output is not mixed up.

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 trying to lock the same mutex will be blocked indefinitely. This can cause your program to hang.

Are there alternatives to using mutexes for thread synchronization?

Yes, alternatives include using std::lock_guard for automatic locking and unlocking, or other synchronization mechanisms like std::condition_variable or std::shared_mutex for more complex scenarios.