在 C++ 中进行事件处理的正确方法是什么？

我有一个应用程序需要按以下方式响应某些事件：

void someMethodWithinSomeClass() {
    while (true) {
        wait for event;
        if (event == SomeEvent) {
            doSomething();
            continue;
        }
        if (event == SomeOtherEvent) {
            doSomethingElse();
            continue;
        }
    } 
}

这将是某个线程正在运行。在其他一些线程中，操作将创建并触发事件。

如何让这些事件到达上述方法/类？在 C++ 中实现事件处理的正确策略或架构是什么？

通常，事件队列被实现为命令设计模式 http://en.wikipedia.org/wiki/Command_pattern:

在面向对象编程中，命令模式是一种设计 使用对象来表示和封装所有内容的模式 稍后调用方法所需的信息。这 信息包括方法名称、拥有该方法的对象 以及方法参数的值。

In C++, 拥有方法和方法参数值的对象是一个空函子（即不带参数的函子）。它可以使用创建boost::bind() or C++11 lambda http://en.wikipedia.org/wiki/C%2B%2B11#Lambda_functions_and_expressions并包裹成boost::function.

这是一个如何在多个生产者线程和多个消费者线程之间实现事件队列的简约示例。用法：

void consumer_thread_function(EventQueue::Ptr event_queue)
try {
    for(;;) {
        EventQueue::Event event(event_queue->consume()); // get a new event 
        event(); // and invoke it
    }
}
catch(EventQueue::Stopped&) {
}

void some_work(int n) {
    std::cout << "thread " << boost::this_thread::get_id() << " : " << n << '\n';
    boost::this_thread::sleep(boost::get_system_time() + boost::posix_time::milliseconds(500));
}

int main()
{
    some_work(1);

    // create an event queue that can be shared between multiple produces and multiple consumers
    EventQueue::Ptr queue(new EventQueue);

    // create two worker thread and pass them a pointer to queue
    boost::thread worker_thread_1(consumer_thread_function, queue);
    boost::thread worker_thread_2(consumer_thread_function, queue);

    // tell the worker threads to do something
    queue->produce(boost::bind(some_work, 2));
    queue->produce(boost::bind(some_work, 3));
    queue->produce(boost::bind(some_work, 4));

    // tell the queue to stop
    queue->stop(true);

    // wait till the workers thread stopped
    worker_thread_2.join();
    worker_thread_1.join();

    some_work(5);
}

Outputs:

./test
thread 0xa08030 : 1
thread 0xa08d40 : 2
thread 0xa08fc0 : 3
thread 0xa08d40 : 4
thread 0xa08030 : 5

执行：

#include <boost/function.hpp>
#include <boost/thread/thread.hpp>
#include <boost/thread/condition.hpp>
#include <boost/thread/mutex.hpp>
#include <boost/smart_ptr/intrusive_ptr.hpp>
#include <boost/smart_ptr/detail/atomic_count.hpp>
#include <iostream>

class EventQueue
{
public:
    typedef boost::intrusive_ptr<EventQueue> Ptr;
    typedef boost::function<void()> Event; // nullary functor
    struct Stopped {};

    EventQueue()
        : state_(STATE_READY)
        , ref_count_(0)
    {}

    void produce(Event event) {
        boost::mutex::scoped_lock lock(mtx_);
        assert(STATE_READY == state_);
        q_.push_back(event);
        cnd_.notify_one();
    }

    Event consume() {
        boost::mutex::scoped_lock lock(mtx_);
        while(STATE_READY == state_ && q_.empty())
            cnd_.wait(lock);
        if(!q_.empty()) {
            Event event(q_.front());
            q_.pop_front();
            return event;
        }
        // The queue has been stopped. Notify the waiting thread blocked in
        // EventQueue::stop(true) (if any) that the queue is empty now.
        cnd_.notify_all();
        throw Stopped();
    }

    void stop(bool wait_completion) {
        boost::mutex::scoped_lock lock(mtx_);
        state_ = STATE_STOPPED;
        cnd_.notify_all();
        if(wait_completion) {
            // Wait till all events have been consumed.
            while(!q_.empty())
                cnd_.wait(lock);
        }
        else {
            // Cancel all pending events.
            q_.clear();
        }
    }

private:
    // Disable construction on the stack. Because the event queue can be shared between multiple
    // producers and multiple consumers it must not be destroyed before the last reference to it
    // is released. This is best done through using a thread-safe smart pointer with shared
    // ownership semantics. Hence EventQueue must be allocated on the heap and held through
    // smart pointer EventQueue::Ptr.
    ~EventQueue() {
        this->stop(false);
    }

    friend void intrusive_ptr_add_ref(EventQueue* p) {
        ++p->ref_count_;
    }

    friend void intrusive_ptr_release(EventQueue* p) {
        if(!--p->ref_count_)
            delete p;
    }

    enum State {
        STATE_READY,
        STATE_STOPPED,
    };

    typedef std::list<Event> Queue;
    boost::mutex mtx_;
    boost::condition_variable cnd_;
    Queue q_;
    State state_;
    boost::detail::atomic_count ref_count_;
};