boost TCP 服务器在 Linux 下无法正确接受连接

服务器线程已从此处修改。评论很能说明问题：

// don't break, keep looping, else we may exit before a connection is actually established

事实并非如此。在建立连接之前看到它退出的原因是 IO 服务耗尽了工作。由于你让服务耗尽了工作，所以循环是没有意义的，除非你真的使用了 restart（）：

对 、 或 的后续调用将立即返回，除非之前调用了run()run_one()poll()poll_one()restart()

因此，真正的解决方法是保持循环的预期，但在开始之前放置工作，例如更改

std::thread serverThread(server_thread_func, std::ref(ioc));
do_accept_connection(m_acceptor, ioc);

自

do_accept_connection(m_acceptor, ioc);
std::thread serverThread(server_thread_func, std::ref(ioc));

其他问题

全局连接变量是一个问题，尤其是当您接受 1 个以上的连接时。通过不使用全局来修复它，例如：

void on_accept_connection(std::error_code ec, std::shared_ptr<tcp::socket> s) {
    if (!ec)
        std::cout << "SERVER ACCEPTED CONNECTION from " << s->remote_endpoint() << std::endl;
    else
        std::cout << "Reader connection error " << ec << " (" << ec.message() << ")" << std::endl;
}

void do_accept_connection(tcp::acceptor& acceptor, asio::io_context& service) {
    auto s = std::make_shared<tcp::socket>(service);
    acceptor.async_accept(*s, bind(on_accept_connection, _1, s));
}

请注意我们如何将共享指针绑定到完成处理程序中，以使其保持活动状态。

这已经有效了：https://coliru.stacked-crooked.com/a/df135c6936c5e37e

Connecting socket...
Connected socket
SERVER ACCEPTED CONNECTION from 127.0.0.1:45958
[eventloop] exit
Closing socket

修复一切

但是，您应该采用移动套接字的重载，使用内置线程池，不使用第二个 io 服务，使用而不是已弃用的和其他东西，例如不使用不必要的原始指针（或完全绑定）和传递执行上下文而不是执行器等： Live On Coliruio_contextio_serviceboost::bindboost::thread

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

namespace asio = boost::asio;
using namespace std::chrono_literals;
using boost::asio::ip::tcp;

void on_accept_connection(std::error_code ec, tcp::socket s) {
    if (!ec)
        std::cout << "Accepted from " << s.remote_endpoint() << std::endl;
    else
        std::cout << std::endl;
}

void accept_loop(tcp::acceptor& acc) {
    acc.async_accept(make_strand(acc.get_executor()), on_accept_connection);
}

int main() {
    tcp::endpoint ep{{}, 1900};
    using std::this_thread::sleep_for;

    asio::thread_pool ioc(1);

    tcp::acceptor listener{ioc, ep};
    accept_loop(listener);

    sleep_for(500ms);

    {
        // start client:
        tcp::socket socket(ioc);

        std::cout << "Connecting socket..." << std::endl;
        socket.connect(ep);
        std::cout << "Connected socket" << std::endl;

        sleep_for(500ms);
        std::cout << "Closing socket" << std::endl;
    }

    ioc.join();
}

印刷

Connecting socket...
Connected socket
Accepted from 127.0.0.1:47014
Closing socket

奖金

为了使它完整，实际上make loop：accept_loop

在 Coliru 上直播

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

namespace asio = boost::asio;
using namespace std::chrono_literals;
using boost::system::error_code;
using boost::asio::ip::tcp;

struct session : std::enable_shared_from_this<session> {
    session(tcp::socket s) : s_(std::move(s)) {}

    void run() {
        std::cout << "Session from " << s_.remote_endpoint() << std::endl;
        async_write(s_,
                    asio::buffer(message_), //
                    consign(asio::detached, shared_from_this()));
    }

  private:
    tcp::socket s_;
    std::string message_ = "Hello from server\n";
};

struct listener {
    listener(tcp::endpoint ep) : acc_(ioc_, ep) { accept_loop(); }

  private:
    asio::thread_pool ioc_{1};
    tcp::acceptor     acc_;

    void accept_loop() {
        acc_.async_accept(make_strand(acc_.get_executor()), [this](error_code ec, tcp::socket s) {
            if (!ec) {
                std::make_shared<session>(std::move(s))->run();
                accept_loop();
            } else
                std::cout << std::endl;
        });
    }
};

int main() {
    tcp::endpoint ep{{}, 1900};
    listener      server(ep);

    std::this_thread::sleep_for(50ms);

    for (auto i = 0; i < 10; ++i) {
        tcp::iostream is(ep);
        std::cout << "Connected: " << is.rdbuf() << std::endl;
    }
}

印刷，例如

Connected: Session from 127.0.0.1:48586
Hello from server

Connected: Session from 127.0.0.1:48588
Hello from server

Connected: Session from 127.0.0.1:48590
Hello from server

Connected: Session from 127.0.0.1:48592
Hello from server

Connected: Session from 127.0.0.1:48594
Hello from server

Connected: Session from 127.0.0.1:48596
Hello from server

Connected: Session from 127.0.0.1:48598
Hello from server

Connected: Session from 127.0.0.1:48600
Hello from server

Connected: Session from 127.0.0.1:48602
Hello from server

Connected: Session from 127.0.0.1:48604
Hello from server