c++ - 如何修复C++线程死锁示例

我有一个C++ 11线程死锁。这可以通过使用两个单独的功能以及多个线程池来实现。如何解决此示例以避免死锁？我认为该解决方案与锁定过程的一致顺序有关。

#include <thread>
#include <mutex>
#include <iostream>

std::mutex kettle;
std::mutex tap;

#define THREAD_POOL 8

void kettle_tap(){

    std::cout << "Locking kettle in " << std::this_thread::get_id() << std::endl;
    // Lock the mutex kettle by creating and using lock_guard kettle_lock.
    std::lock_guard<std::mutex> kettle_lock(kettle);
    std::cout << "Locked kettle in " << std::this_thread::get_id() << std::endl;

    std::cout << "Locking tap in " << std::this_thread::get_id() << std::endl;
    // Lock the mutex tap by creating and using lock_guard tap_lock.
    std::lock_guard<std::mutex> tap_lock(tap);
    std::cout << "Locked tap in " << std::this_thread::get_id() << std::endl;

    std::cout << "Filling kettle in " << std::this_thread::get_id() << std::endl;
}

void tap_kettle(){

    std::cout << "Locking tap in " << std::this_thread::get_id() << std::endl;
    // Lock the mutex tap by creating and using lock_guard tap_lock.
    std::lock_guard<std::mutex> tap_lock(tap);
    std::cout << "Locked tap in " << std::this_thread::get_id() << std::endl;

    std::cout << "Locking kettle in " << std::this_thread::get_id() << std::endl;
    // Lock the mutex kettle by creating and using lock_guard kettle_lock.
    std::lock_guard<std::mutex> kettle_lock(kettle);
    std::cout << "Locked kettle in " << std::this_thread::get_id() << std::endl;

    std::cout << "Filling kettle in " << std::this_thread::get_id() << std::endl;

}

int main(){

    std::thread pool[THREAD_POOL];

    for (int t = 0; t < THREAD_POOL; t += 2){
        pool[t]   = std::thread(kettle_tap);
        pool[t+1] = std::thread(tap_kettle);
    }

    for (int t = 0; t < THREAD_POOL; ++t){
        pool[t].join();
    }

    std::cout << "Threads are all joined" << std::endl;

    return 0;

}

最佳答案

std::lock(Mutexes...)
在您的情况下，kettle_tap()和tap_kettle()均应以以下内容开头:

std::lock(tap, kettle);

但是互斥量参数的顺序无关紧要，因此在两个函数之间可以不同。

稍后，如果您要将锁的所有权转让给std::lock_guard:

std::lock(tap, kettle);
std::lock_guard<std::mutex> kettle_lock(kettle, std::adopt_lock);
std::lock_guard<std::mutex> tap_lock(tap, std::adopt_lock);