在不同线程上发布作品时如何将信号连接到 boost::asio::io_service？

Question

我正在尝试使用 boost::lockfree 队列来管理任务。这些任务检索数据并将在工作线程上进行处理。检索数据后，应将信号与数据一起发送到主线程。工作线程在应用程序启动时产生，并不断轮询队列。我是 Boost::Asio 的新手，但根据我的研究，它似乎是在线程之间发送信号的最佳机制。

我看过几个例子，特别是：

Confused when boost::asio::io_service run method blocks/unblocks
boost asio post not working , io_service::run exits right after post

这是我的代码：

#include "stdafx.h"
#include <thread>

#include <boost/asio.hpp>
#include <boost/bind.hpp>
#include <boost/lockfree/spsc_queue.hpp>
#include <boost/optional.hpp>
#include <boost/thread.hpp>
#include <boost/signals2.hpp>

typedef boost::signals2::signal<void(int)> signal_type;

class Task
{
public:
    Task(int handle) : _handle(handle) {};
   ~Task() {};

   virtual void Execute()
   {
      int result = _handle * 2;
   }

private:
   int _handle;
};


class Manager
{
public:
   Manager() 
   {
      _mainService = std::make_shared<boost::asio::io_service>();
      _workerService = std::make_shared<boost::asio::io_service>();
      _work = std::make_shared<boost::asio::io_service::work>(*_workerService);

      _threadStarted = false;
      Start();
   };

   ~Manager() {};

   void WorkerMain()
   {
      _workerService->poll();
   }

   void Start()
   {
      if (_threadStarted) return;

      _workerThread = std::thread(&Manager::WorkerMain, this);
      _threadStarted = true;
   }

   void Stop()
   {
      if (_threadStarted == false) return;

      _mainService->stop();
      _workerThread.join();
      _mainService.reset();
   }

   void OnSignalFetchCompleted(int value)
   {
      int asdf = 0; //do stuff with data on main thread
   }

   void ProcessData(signal_type& signal)
   {
      int i = 0;

      do
      {
         _queue.consume_one([&](std::shared_ptr<Task> task)
         {
            task->Execute();
            //get data from task; send out signal with data
         });

         i++;
      } while (i < 3);
   }

   void QueueData(int handle)
   {
      _signalFetchCompleted.connect(boost::bind(&Manager::OnSignalFetchCompleted, this, _1));
      _workerService->post(boost::bind(&Manager::ProcessData, boost::ref(_signalFetchCompleted))); //!!does not compile

      std::shared_ptr<Task> task = std::make_shared<Task>(handle);
      _queue.push(task);
   }

private:
   boost::lockfree::spsc_queue<std::shared_ptr<Task>, boost::lockfree::capacity<1024>> _queue;
   std::thread _workerThread;
   bool _threadStarted;

   std::shared_ptr<boost::asio::io_service> _mainService;
   std::shared_ptr<boost::asio::io_service> _workerService;
   std::shared_ptr<boost::asio::io_service::work> _work;

   signal_type _signalFetchCompleted;
};


int _tmain(int argc, _TCHAR* argv[])
{
   std::shared_ptr<Manager> mgr = std::make_shared<Manager>();
   mgr->QueueData(5);
   mgr->QueueData(10);

   mgr->Stop();

   return 0;
}

我在 _workerService->Post 行遇到一个我无法解决的编译错误：

1>C:\Boost\boost/bind/mem_fn.hpp(333): error C2784: 'T *boost::get_pointer(const boost::scoped_ptr<T> &)' : could not deduce template argument for 'const boost::scoped_ptr<T> &' from 'const signal_type'
1>          C:\Boost\boost/smart_ptr/scoped_ptr.hpp(150) : see declaration of 'boost::get_pointer'
1>          C:\Boost\boost/bind/mem_fn.hpp(352) : see reference to function template instantiation 'R (__cdecl &boost::_mfi::dm<R,Manager>::call<const U>(U &,const void *) const)' being compiled
1>          with
1>          [
1>              R=void (signal_type &)
1>  ,            U=signal_type
1>          ]
1>          C:\Boost\boost/bind/mem_fn.hpp(352) : see reference to function template instantiation 'R (__cdecl &boost::_mfi::dm<R,Manager>::call<const U>(U &,const void *) const)' being compiled
1>          with
1>          [
1>              R=void (signal_type &)
1>  ,            U=signal_type
1>          ]
1>          C:\Boost\boost/bind/bind.hpp(243) : see reference to function template instantiation 'R (__cdecl &boost::_mfi::dm<R,Manager>::operator ()<T>(const U &) const)' being compiled
1>          with
1>          [
1>              R=void (signal_type &)
1>  ,            T=signal_type
1>  ,            U=signal_type
1>          ]

对于解决此编译错误的任何帮助或对此方法的一般评论，我们将不胜感激。谢谢。

Answer 1

编译器错误似乎是在谈论您构建了一个 boost::asio::io_service::work 对象并且您向其传递了不正确的参数：

error C2664: 'boost::asio::io_service::work::work(const boost::asio::io_service::work &)' : cannot convert argument 1 from 'std::shared_ptr<boost::asio::io_service>' to 'boost::asio::io_service &'

boost::asio::io_service::work 有一个构造函数，它接受一个 boost::asio::io_service& 和一个复制构造函数；但是，您传递的是 std::shared_ptr<boost::asio::io_service>:

_work = std::make_shared<boost::asio::io_service::work>(_workerService);

在这里，_workerService是一个std::shared_ptr<boost::asio::io_service>，但是你需要一个boost::asio::io_service&。请尝试以下操作：

_work = std::make_shared<boost::asio::io_service::work>(*_workerService);

Answer 2

我认为 boost::asio 不是您任务的最佳解决方案。你读过条件变量吗？它们要简单得多，可用于实现您的目标。

Answer 3

根据新信息，问题出在您的 boost::bind 上。您正在尝试调用一个没有对象的成员函数来调用它：您正在尝试调用 ProcessData 但您没有告诉绑定您希望在哪个对象上调用它。你需要给它一个 Manager 来调用它：

_workerService->post(boost::bind(&Manager::ProcessData, this, boost::ref(_signalFetchCompleted)));

这将在 this 上调用 ProcessData 并传入对 _signalFetchCompleted

的引用

在不同线程上发布作品时如何将信号连接到 boost::asio::io_service？

How to connect signal to boost::asio::io_service when posting work on different thread?

c++

multithreading

boost

boost-asio

signals-slots