當調用條件變量的通知時，互斥鎖是否會被解鎖

我想了解互斥鎖在條件變量中使用時會發生什麼。當調用條件變量的通知時，互斥鎖是否會被解鎖

在以下示例中，從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(); 
}

採取的生產者線程調用cond_var.notify_one（）互斥被解鎖之前。當通知被調用時互斥鎖m是否被解鎖，或者僅當互斥鎖被解鎖時纔會發生通知？

來源

2012-10-22 danny