c++ - boost::asio::deadline_timer 不调用处理程序

Question

我有一个 tcp 客户端，它会在截止日期前轮询服务器以获得答案，这样如果无法访问服务器，客户端就不会被阻止。我遇到的问题是 async_wait 似乎从不调用它的处理程序，在连接失败时有效地阻塞了客户端。每次调用 tcpPoll 都会有自己的线程(这就是我创建新的 io_service 的原因)，但即使没有多线程，它似乎也无法工作。此外，NetworkEntity 对象在其生命周期内可以多次调用 tcpPoll。

我的问题是:什么阻止了 deadline_timer 调用它的处理程序？ (以及如何解决)

这里是一些相关的代码，只要没有失败(连接、写入、读取)，它就可以工作(如果有点长，抱歉):

void NetworkEntity::stop()
{
    stopped_ = true;
    //close socket
    //cancel timeout
}

void NetworkEntity::check_timeout(const boost::system::error_code& error)
{
    if (stopped_)
        return;
    if (timeout_.expires_at() <= boost::asio::deadline_timer::traits_type::now())
    {
        stop();
        timeout_.expires_at(boost::posix_time::pos_infin);
        std::cout << address_ << " timed out\n";
    }
    timeout_.async_wait(boost::bind(&NetworkEntity::check_timeout, this, boost::asio::placeholders::error));
}

std::vector<std::string> NetworkEntity::tcpPoll(const char* message, const char endOfMessage)
{
    boost::asio::io_service io_service;
    stopped_ = false;
    timeout_.expires_from_now(boost::posix_time::seconds(TIMEOUT_));
    timeout_.async_wait(boost::bind(&NetworkEntity::check_timeout, this, boost::asio::placeholders::error));
    tcp::resolver resolver(io_service);
    start_connect(&io_service, resolver.resolve(tcp::resolver::query(address_, port_)), message, endOfMessage);
    io_service.run();
    //retrieve answer from class
    //return answer
}

void NetworkEntity::start_connect(boost::asio::io_service* io_service, tcp::resolver::iterator endpoint_iterator, const std::string message, const char endOfMessage)
{
    socket_.reset(new tcp::socket(*io_service));
    socket_->async_connect(endpoint_iterator->endpoint(),
        boost::bind(&NetworkEntity::handle_connect, this, io_service, boost::asio::placeholders::error, endpoint_iterator, message, endOfMessage));
}

void NetworkEntity::handle_connect(boost::asio::io_service* io_service, const boost::system::error_code& err, tcp::resolver::iterator endpoint_iterator, const std::string message, const char endOfMessage)
{
    if(stopped_)
        return;
    if (err)
    {
        std::cout << "Connect error: " << err.message() << "\n";
        stop();
    }
    else
    {
        start_write(message, endOfMessage);
    }
}

void NetworkEntity::start_write(const std::string message, const char endOfMessage)
{
    std::ostream request_stream(&request_);
    request_stream << message;
    boost::asio::async_write(*socket_, request_,
        boost::bind(&NetworkEntity::handle_write, this, boost::asio::placeholders::error, endOfMessage));
}

void NetworkEntity::handle_write(const boost::system::error_code& error, const char endOfMessage)
{
    if (stopped_)
        return;
    if (!error)
    {
        //sleep for 500ms to let time for the reciever to process info (had a bug on this one)
        start_read(endOfMessage);
    }
    else
    {
        std::cout << "write error : " << error.message() << "\n";
        stop();
    }
}

void NetworkEntity::start_read(const char endOfMessage)
{
    boost::asio::async_read_until(*socket_, answer_, endOfMessage,
        boost::bind(&NetworkEntity::handle_read, this, boost::asio::placeholders::error));
}

void NetworkEntity::handle_read(const boost::system::error_code& error)
{
    if (stopped_)
        return;
    if (error)
    {
        std::cout << "read error : " << error.message() << "\n";
        stop();
    }
    else
    {
        stop();
    }
}

Answer 1

我认为您一定对 io_service 的多个实例感到困惑。

我认为这是因为在您的代码中您从未显示如何初始化timeout_。而您用于连接的 io_service 实例仅在您的 tcpPoll 函数中实例化...这让我相信您不小心在一个单独的服务器上注册了截止时间计时器你甚至不运行的 io_service？

这是一个实际有效的版本，注意:

1. 它已经取消了 stopped_ bool 值，因为它是不必要的并且必然会造成混淆
2. 查看 check_timeout 和 stop 的新实现，了解如何检测各种程序流
3. 完整的代码，独立的，只比你在问题中发布的多几行代码

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

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

struct NetworkEntity {

    boost::asio::io_service io_service;
    boost::asio::deadline_timer timeout_{io_service};
    std::string address_ = "localhost";
    std::string port_    = "6767";
    int TIMEOUT_         = 3;
    boost::shared_ptr<tcp::socket> socket_;
    boost::asio::streambuf request_, answer_;

    void stop()
    {
        if (socket_)
        {
            socket_->cancel();
            socket_->close();
        }
        timeout_.cancel();
        io_service.stop();
    }

    void check_timeout(const boost::system::error_code& error)
    {
        if (error != boost::asio::error::operation_aborted)
        {
            stop();
            std::cout << address_ << " timed out\n";
        }
        timeout_.async_wait(boost::bind(&NetworkEntity::check_timeout, this, boost::asio::placeholders::error));
    }

    std::vector<std::string> tcpPoll(const char* message, const char endOfMessage)
    {
        timeout_.expires_from_now(boost::posix_time::seconds(TIMEOUT_));
        timeout_.async_wait(boost::bind(&NetworkEntity::check_timeout, this, boost::asio::placeholders::error));

        tcp::resolver resolver(io_service);
        start_connect(&io_service, resolver.resolve(tcp::resolver::query(address_, port_)), message, endOfMessage);

        io_service.run();
        //retrieve answer from class
        //return answer
        std::ostringstream oss;
        oss << &answer_;
        return { oss.str() };
    }

    void start_connect(boost::asio::io_service* io_service, tcp::resolver::iterator endpoint_iterator, const std::string message, const char endOfMessage)
    {
        socket_.reset(new tcp::socket(*io_service));
        socket_->async_connect(endpoint_iterator->endpoint(),
                boost::bind(&NetworkEntity::handle_connect, this, io_service, boost::asio::placeholders::error, endpoint_iterator, message, endOfMessage));
    }

    void handle_connect(boost::asio::io_service* io_service,
            const boost::system::error_code& err,
            tcp::resolver::iterator endpoint_iterator,
            const std::string message,
            const char endOfMessage)
    {
        if (err)
        {
            std::cout << "Connect error: " << err.message() << "\n";
            stop();
        }
        else
        {
            start_write(message, endOfMessage);
        }
    }

    void start_write(const std::string message, const char endOfMessage)
    {
        std::ostream request_stream(&request_);
        request_stream << message;
        boost::asio::async_write(*socket_, request_,
                boost::bind(&NetworkEntity::handle_write, this, boost::asio::placeholders::error, endOfMessage));
    }

    void handle_write(const boost::system::error_code& error, const char endOfMessage)
    {
        if (!error)
        {
            //sleep for 500ms to let time for the reciever to process info (had a bug on this one)
            start_read(endOfMessage);
        }
        else
        {
            std::cout << "write error : " << error.message() << "\n";
            stop();
        }
    }

    void start_read(const char endOfMessage)
    {
        boost::asio::async_read_until(*socket_, answer_, endOfMessage,
                boost::bind(&NetworkEntity::handle_read, this, boost::asio::placeholders::error));
    }

    void handle_read(const boost::system::error_code& error)
    {
        if (error)
        {
            std::cout << "read error : " << error.message() << "\n";
        }
        stop();
    }
};

int main()
{
    NetworkEntity ne;
    for (auto& s : ne.tcpPoll("this is my request", '\n'))
    {
        std::cout << "Line: '" << s << "'\n";
    }
}