如何将异步计时器添加到 boost UDP 服务器？

Question

我在网上获得了这段代码，并一直在尝试为其添加一个计时器，以便它每隔一段时间读取一个数据包。我似乎无法弄清楚如何将回调函数传递给 boost::async_wait 命令，因为我收到了这个错误：

server1.cpp: In member function ‘void UDPClient::handle_receive(const boost::system::error_code&, size_t)’:
server1.cpp:51:66: error: invalid use of non-static member function ‘void UDPClient::time_to_receive(const boost::system::error_code&)’
                                  boost::asio::placeholders::error));
                                                                  ^
server1.cpp:33:6: note: declared here
 void UDPClient::time_to_receive(const boost::system::error_code& error)
      ^~~~~~~~~

UDPClient 类：

#include <boost/asio.hpp>
#include <boost/bind.hpp>
#include <boost/array.hpp>
#include <iostream>
#include <boost/date_time/posix_time/posix_time.hpp>

using boost::asio::ip::udp;

class UDPClient
{
public:
    boost::asio::io_service io_service;
    udp::socket socket;
    udp::endpoint receiver_endpoint;
    boost::asio::deadline_timer timer;
    boost::array<char, 1024> recv_buffer;

    UDPClient();
    void time_to_receive(const boost::system::error_code& error);
    void do_receive();
    void handle_receive(const boost::system::error_code& error, size_t);
};

UDPClient::UDPClient()
    : io_service(),
      socket(io_service, {udp::v4(), 3643}),
      timer(io_service, boost::posix_time::seconds(2))
{
    do_receive();
    io_service.run();
}

void UDPClient::time_to_receive(const boost::system::error_code& error)
{
    do_receive();
}

void UDPClient::do_receive()
{
    socket.async_receive_from(boost::asio::buffer(recv_buffer), receiver_endpoint,
                               boost::bind(&UDPClient::handle_receive, this,
                               boost::asio::placeholders::error,
                               boost::asio::placeholders::bytes_transferred));
}

void UDPClient::handle_receive(const boost::system::error_code& error, size_t bytes_transferred)
{
    std::cout << "Received: '" << std::string(recv_buffer.begin(), recv_buffer.begin()+bytes_transferred) << "'\n";

    timer.async_wait(boost::bind(time_to_receive,
                                 boost::asio::placeholders::error));
}

int main()
{
    UDPClient updclient;
}

我试图用这段代码回答的一个问题是，如果我用一堆 UDP 数据包从客户端向服务器发送垃圾邮件，服务器会在 async_wait 期间忽略所有数据包吗？

另外，我的主要目标是将此代码放入我拥有的四轴飞行器代码中。它会按照编写该类的方式工作，并让它从地面站读取数据包以获取用户输入吗？

Answer 1

您使用bind 与成员函数的方式是错误的。如下所示使用它：

timer.async_wait(boost::bind(&UDPClient::time_to_receive, this,
                             boost::asio::placeholders::error));

至于为什么会这样，我建议你阅读 boost 文档。

此外，我还修改了代码，使其像服务器一样实际运行而无需退出。为此，我做了以下 2 处更改：

1. 在主函数中初始化io_service，并将其引用传递给类。
2. 初始化io_service_work 对象。这是io_service 的常年工作来源。因此，io_service 永远不会从 run 函数返回，除非 work 对象被销毁。

完整来源：

#include <boost/asio.hpp>
#include <boost/bind.hpp>
#include <boost/array.hpp>
#include <iostream>
#include <boost/date_time/posix_time/posix_time.hpp>

using boost::asio::ip::udp;

class UDPClient
{
public:
    boost::asio::io_service& io_service;
    udp::socket socket;
    udp::endpoint receiver_endpoint;
    boost::asio::deadline_timer timer;
    boost::array<char, 1024> recv_buffer;

    UDPClient(boost::asio::io_service&);
    void time_to_receive(const boost::system::error_code& error);
    void do_receive();
    void handle_receive(const boost::system::error_code& error, size_t);
};

UDPClient::UDPClient(boost::asio::io_service& ios)
    : io_service(ios),
      socket(io_service, {udp::v4(), 3643}),
      timer(io_service, boost::posix_time::seconds(2))
{
    do_receive();
}

void UDPClient::time_to_receive(const boost::system::error_code& error)
{
    do_receive();
}

void UDPClient::do_receive()
{
    socket.async_receive_from(boost::asio::buffer(recv_buffer), receiver_endpoint,
                               boost::bind(&UDPClient::handle_receive, this,
                               boost::asio::placeholders::error,
                               boost::asio::placeholders::bytes_transferred));
}

void UDPClient::handle_receive(const boost::system::error_code& error, size_t bytes_transferred)
{
    std::cout << "Received: '" << std::string(recv_buffer.begin(), recv_buffer.begin()+bytes_transferred) << "'\n";
    timer.expires_from_now(boost::posix_time::seconds(2));
    timer.async_wait(boost::bind(&UDPClient::time_to_receive, this,
                                 boost::asio::placeholders::error));
}

int main()
{
  boost::asio::io_service ios;
  boost::asio::io_service::work wrk(ios);
  UDPClient updclient(ios);
  ios.run();
}

注意：虽然它是一个服务器，但类名是Client。我忽略了:)