<mutex>

<mutex> provides std::mutex for mutual exclusion, and std::lock_guard<Mutex> / std::unique_lock<Mutex> for RAII-based locking. Always lock via a lock guard to ensure the lock is released even if an exception is thrown.

Use std::lock_guard for simple cases; use std::unique_lock when you need to unlock before scope end or transfer lock ownership.

This example protects a shared counter with a mutex, having two threads each increment it 100 times safely.

// compile: g++ -std=c++11 -pthread -o mutexexample mutexexample.cpp
// run: ./mutexexample
// description: protect shared data with mutex
 
#include <mutex>
#include <iostream>
#include <thread>
 
int counter = 0;
std::mutex mtx;
 
void increment() {
    for (int i = 0; i < 100; ++i) {
        std::lock_guard<std::mutex> lock(mtx);
        counter++;
    }
}
 
int main() {
    std::thread t1(increment);
    std::thread t2(increment);
 
    t1.join();
    t2.join();
 
    std::cout << "final counter: " << counter << "\n";
 
    return 0;
}