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 accessed by multiple threads simultaneously. In C++, you can use the std::mutex class from the <mutex> header 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 only one thread accesses the output at a time.

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 mutex will be blocked indefinitely. This can cause your program to hang.

Are there alternatives to using mutexes for synchronization?

Yes, there are alternatives like std::lock_guard for automatic locking and unlocking, or using condition variables for more complex synchronization scenarios.