Search⌘ K
AI Features
Home
Courses
Modern C++ Concurrency: Get the most out of any machine

Introduction to Mutexes

Explore how mutexes provide mutual exclusion in C++ multithreading by allowing only one thread at a time to access critical code sections. Understand the synchronization of concurrent threads to avoid data races and race conditions, and learn why std::cout is thread-safe yet can display interleaved output.

We'll cover the following...

Mutex stands for mutual exclusion. It ensures that only one thread can access a critical section at any one time. By using a mutex, concurrent threads are synchronized, preventing interleaved output or data corruption.

C++
// coutSynchronised.cpp
#include <chrono>
#include <iostream>
#include <mutex>
#include <thread>
std::mutex coutMutex;
class Worker{
public:
  Worker(std::string n):name(n){};
 
    void operator() (){
      for (int i = 1; i <= 3; ++i){ 
        // begin work
        std::this_thread::sleep_for(std::chrono::milliseconds(200));
        // end work
        coutMutex.lock();
        std::cout << name << ": " << "Work " << i << " done !!!" << std::endl;
        coutMutex.unlock();
      }
    }
private:
  std::string name;
};
int main(){
  std::cout << std::endl;
  
  std::cout << "Boss: Let's start working." << "\n\n";
 
  std::thread herb= std::thread(Worker("Herb"));
  std::thread andrei= std::thread(Worker("  Andrei"));
  std::thread scott= std::thread(Worker("    Scott"));
  std::thread bjarne= std::thread(Worker("      Bjarne"));
  std::thread bart= std::thread(Worker("        Bart"));
  std::thread jenne= std::thread(Worker("          Jenne"));
  
  herb.join();
  andrei.join();
  scott.join();
  bjarne.join();
  bart.join();
  jenne.join();
  
  std::cout << "\n" << "Boss: Let's go home." << std::endl;
  
  std::cout << std::endl;
}

Essentially, when the lock is set on a mutex, no other ...