我正在研究C++中的并发性，并且我正在尝试实现一个多线程回调注册系统。我产生了下面的代码，它应该接受注册请求，直到一个事件发生。在那之后，它应该按照它们被注册的顺序执行所有注册的回调。注册顺序不必是确定的。代码没有按照预期工作。首先，它很少输出“Pushing callback with id”消息。其次，它有时候会挂起（我认为是由争用条件引起的死锁）。我希望能得到帮助，以弄清楚这里发生了什么。如果您发现我使代码的某些部分过于复杂或误用了某些部分，也请指出这一点。

#include <condition_variable>
#include <functional>
#include <iostream>
#include <mutex>
#include <queue>
#include <thread>

class CallbackRegistrar{
public:
    void registerCallbackAndExecute(std::function<void()> callback) {
        if (!eventTriggered) {
            std::unique_lock<std::mutex> lock(callbackMutex);
            auto saved_id = callback_id;
            std::cout << "Pushing callback with id " << saved_id << std::endl;
            registeredCallbacks.push(std::make_pair(callback_id, callback));
            ++callback_id;
            callbackCond.wait(lock, [this, saved_id]{return releasedCallback.first == saved_id;});
            releasedCallback.second();
            callbackExecuted = true;
            eventCond.notify_one();
        }
        else {
            callback();
        }
    }
    void registerEvent() {
        eventTriggered = true;
        while (!registeredCallbacks.empty()) {
            releasedCallback = registeredCallbacks.front();
            callbackCond.notify_all();
            std::unique_lock<std::mutex> lock(eventMutex);
            eventCond.wait(lock, [this]{return callbackExecuted;});
            callbackExecuted = false;
            registeredCallbacks.pop();
        }
    }
private:
    std::queue<std::pair<unsigned, std::function<void()>>> registeredCallbacks;
    bool eventTriggered{false};
    bool callbackExecuted{false};
    std::mutex callbackMutex;
    std::mutex eventMutex;
    std::condition_variable callbackCond;
    std::condition_variable eventCond;
    unsigned callback_id{1};
    std::pair<unsigned, std::function<void()>> releasedCallback;
};

int main()
{
    CallbackRegistrar registrar;
    std::thread t1(&CallbackRegistrar::registerCallbackAndExecute, std::ref(registrar), []{std::cout << "First!\n";});
    std::thread t2(&CallbackRegistrar::registerCallbackAndExecute, std::ref(registrar), []{std::cout << "Second!\n";});
    
    registrar.registerEvent();
    
    t1.join();
    t2.join();

    return 0;
}