I am trying to understand what happens to a mutex when it is used in a condition variable.
In the following example, taken from cppreference
int main() { std::queue<int> produced_nums; std::mutex m; std::condition_variable cond_var; bool done = false; bool notified = false; std::thread producer([&]() { for (int i = 0; i < 5; ++i) { std::this_thread::sleep_for(std::chrono::seconds(1)); std::unique_lock<std::mutex> lock(m); std::cout << "producing " << i << '\n'; produced_nums.push(i); notified = true; cond_var.notify_one(); } done = true; cond_var.notify_one(); }); std::thread consumer([&]() { std::unique_lock<std::mutex> lock(m); while (!done) { while (!notified) { // loop to avoid spurious wakeups cond_var.wait(lock); } while (!produced_nums.empty()) { std::cout << "consuming " << produced_nums.front() << '\n'; produced_nums.pop(); } notified = false; } }); producer.join(); consumer.join(); } The producer thread calls cond_var.notify_one() before the mutex gets unlocked. Does the mutex m get unlocked when notify is called, or does the notification occurs only when the mutex gets unlocked?
