C++boost::boost的accept处理程序中的asio可变模板运算符::asio::basic\u socket\u acceptor::async\u accept()

在意识到真正的错误之后 :

好消息是:只需更改一行即可修复错误:

typedef callback<boost::function<void(const boost::system::error_code&, session_ptr&)>> accept_handler;

进入

typedef callback<boost::function<void(const boost::system::error_code&)>> accept_handler;

出于各种原因,之前的定义完全错误:

• 它不符合处理程序的要求
• 它也不符合 bind 表达式: bind(&server::handle_accept, this, asio::placeholders::error, new_session) . 注意,它只有一个占位符( asio::placeholders::error )所以它不可能在两个参数下工作

Live On Coliru

#include <boost/function.hpp>
#include <boost/asio.hpp>
#include <boost/bind.hpp>

namespace ba = boost::asio;
using ba::ip::tcp;

struct session : std::enable_shared_from_this<session> {
    session(ba::io_service& svc) : _socket(svc) {}

    void start() {} // do something asynchronously
    tcp::socket& socket() { return _socket; }

    tcp::socket _socket;
};

using session_ptr = std::shared_ptr<session>;

template <typename Function>
struct callback
{
   Function func_;

   callback(Function&& f = {}) : func_(std::forward<Function>(f)) {
   }

   template <typename ...Args>
   void operator() (Args&& ...args) {
       func_(std::forward<Args>(args)...);
   }
};

class server
{
private:
    typedef callback<boost::function<void(const boost::system::error_code&)>> accept_handler;

    ba::io_service& io_service_;
    tcp::acceptor acceptor_;
    accept_handler handler_;

public:
    server(ba::io_service& io_service, short port)
        : io_service_(io_service),
          acceptor_(io_service, tcp::endpoint(tcp::v4(), port))
    {
        session_ptr new_session = session_ptr(new session(io_service_));
        handler_ = accept_handler(bind(&server::handle_accept, this, ba::placeholders::error, new_session));

        acceptor_.async_accept(new_session->socket(), handler_);
    }

    void handle_accept(const boost::system::error_code& error, session_ptr new_session)
    {
        if (!error)
        {
            new_session->start();
            new_session.reset(new session(io_service_));

            acceptor_.async_accept(new_session->socket(),
                                   handler_);

        }
    }
};

int main() {
}

简化:删除冗余包装

callback<> , accept_handler 有任何用途:

Live On Coliru

class server
{
private:
    ba::io_service& io_service_;
    tcp::acceptor acceptor_;

public:
    server(ba::io_service& io_service, short port)
        : io_service_(io_service),
          acceptor_(io_service, tcp::endpoint(tcp::v4(), port))
    { 
        do_accept();
    }

    void do_accept() {
        session_ptr new_session = session_ptr(new session(io_service_));
        acceptor_.async_accept(new_session->socket(), bind(&server::handle_accept, this, ba::placeholders::error, new_session));
    }

    void handle_accept(const boost::system::error_code& error, session_ptr new_session)
    {
        if (!error) {
            new_session->start();
            do_accept();
        }
    }
};

更简单的方法:捕获Lambda

您可以不使用绑定、占位符和 handle_accept 所有成员同时:

Live On Coliru

class server
{
private:
    ba::io_service& io_service_;
    tcp::acceptor acceptor_;

public:
    server(ba::io_service& io_service, short port)
        : io_service_(io_service),
          acceptor_(io_service, tcp::endpoint(tcp::v4(), port))
    { 
        do_accept();
    }

    void do_accept() {
        session_ptr new_session = std::make_shared<session>(io_service_);

        acceptor_.async_accept(new_session->socket(), [this,new_session](const boost::system::error_code& error) {
            if (!error) {
                new_session->start();
                do_accept();
            }
        });
    }
};

旧答案

在第一次阅读中,我假设您遇到了一个我在Boost Asio和多态Lambda中经常遇到的经典陷阱。很抱歉

事实上,在可变情况下,概念检查无法验证处理器要求。我在这里的方法是禁用需求检查:

#define BOOST_ASIO_DISABLE_HANDLER_TYPE_REQUIREMENTS 1

如果存在不匹配,则丢失的主要信息是更友好的错误消息:

• 当完成处理程序不满足必要的类型要求时,添加了更友好的编译器错误。当C++0x可用时(当前支持g++4.5或更高版本,以及MSVC 10),静态_断言也用于生成信息性错误消息。可以通过定义BOOST\u ASIO\u DISABLE\u HANDLER\u TYPE\u要求来禁用此检查。

看见 http://www.boost.org/doc/libs/1_65_1/doc/html/boost_asio/history.html