使用use_future的Boost Asio async_send_to多播不起作用 [英] Boost Asio async_send_to multicast with use_future does not work

问题描述

ITNOA

我有一个程序想要将带有async_send_to的消息发送到一个多播组.但我想此操作阻止了异步操作，因此我使用use_future来实现此目标，如下所示:

I have program that want to send a message with async_send_to to one multicast group. but I want to this action is blocking not async, so I use use_future for achieve this goal like below

gw::BoostMessageSender::BoostMessageSender(const std::string& group_address, const std::string& interface_name, uint16_t port_number, ba::io_context& io_context)
    : AbstractMessageSender(group_address, interface_name, port_number)
    , io_context(io_context)
    , endpoint(ba::ip::address::from_string(group_address), port_number)
    , socket(io_context, endpoint.protocol())
{
    if (!socket.is_open())
        socket.open(endpoint.protocol());

    socket.set_option(ba::ip::udp::socket::reuse_address(true));
}

bool gw::BoostMessageSender::send(const std::string& message) noexcept
{    
    std::future<std::size_t> result = socket.async_send_to(ba::buffer(message), endpoint, ba::use_future);

    return result.get() == message.size();
}

我像下面这样使用此类

int main()
{
    const string group_address = "235.127.1.1";
    constexpr uint16_t PORT_NUMBER = 8765;

    boost::asio::io_context io_context;

    BoostMessageSender message_sender(group_address, "eth1", PORT_NUMBER, io_context);

    std::thread t1([&io_context]()
        {
            io_context.run();
        });

    this_thread::sleep_for(1s);

    message_sender.send("Any bodey there?");

    cout << "send message: "; // --- this line is not run never :(((
    
    io_context.stop();
    t1.join();
    return 0;
}

我的问题是为什么发送消息不会在控制台中永远不会写?

My problem is why send message does not write in my console never?

陌生人，就是说，我使用 tcpdump -i eth0 -nnSX端口8765 检查我的网络，并在调用 async_send_to 后看到发送到网络的多播消息，但是 result.get()从不返回结果并挂在其上.

Stranger that is, I check my network with tcpdump -i eth0 -nnSX port 8765 and after call async_send_to I can see multicast message that sent to network, but result.get() never return result and hung on that.

我哪里错了?

我在以下平台上测试了这些代码

I test these code on below platforms

Visual Studio 2019 16.7.4
Windows 10 1909 latest update
Boost 1.73.0

Ubuntu 20.04.1 LTS
GCC 9.3.0
Boost 1.71.0

推荐答案

io_context :: run 在没有待执行的待处理作业时返回.

io_context::run returns when there is no pending jobs to be executed.

您可以创建工作警卫以确保即使未启动异步任务也不会完成运行.使用 make_work_guard 函数:

You can create work guard to ensure that run doesn't finish even if no async tasks were initiated. Use make_work_guard function:

boost::asio::io_context io_context;
auto workGuard = boost::asio::make_work_guard(io_context);

这篇关于使用use_future的Boost Asio async_send_to多播不起作用的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！